Organic Chemistry I

Mohammad Jafarzadeh Faculty of Chemistry, Razi University

Organic Chemistry, Structure and Function (7th edition) By P. Vollhardt and N. Schore, Elsevier, 2014 1 2-4 Functional Groups: Centers of Reactivity CHAPTER 2 69

by an acid dissociation constant Ka. Removal of a proton from an acid generates its conjugate base; attachment of a proton to a base forms its conjugate acid. Lewis bases donate an electron pair to form a covalent bond with Lewis acids, a process depicted by a curved arrow pointing from the lone pair of the base toward the acid. Electrophiles and nucleophiles are species in organic chemistry that interact very much like acids and bases. The carbon–halogen bond in the haloalkane is its functional group. It contains an electrophilic carbon atom, which reacts with nucleophiles in a process called nucleophilic substitution.

2-4 FUNCTIONAL GROUPS: CENTERS OF REACTIVITY Many organic molecules consist predominantly of a backbone of carbons linked by single bonds, Manywith only organichydrogen moleculesatoms consistattached predominantly. They ofmay a backbonealso contain of carbonsdoubly linkedor triplyby singlebonded carbons,bonds,as well withas onlyother hydrogenelements atoms. attached. However, they may also contain doubly or R Function triply bonded carbons, as well as other elements. These atoms or groups of atoms tend to These atomsbe sitesor of groupscomparativelyof atoms high tendchemicalto be reactivitysites of andcomparatively are referred to highas functionalchemical groupsreactivity and areorreferred functionalities.to as functional Such groupsgroups have characteristicor functionalities properties,. and they control the reactiv- Carbon frame Functional ity of the molecule as a whole. provides group imparts Such groups have characteristic properties, and they control the reactivity of the molecule structure reactivity as a wholeHydrocarbons. are molecules that contain only hydrogen and carbon Hydrocarbons are molecules that contain only hydrogen and carbon We begin our study with hydrocarbons, which have the general empirical formula CxHy. Those containing only single bonds, such as methane, ethane, and propane, are called The generalalkanes.empirical Moleculesformula such asC cyclohexane,xHy, containing whoseonly carbonssingle formbonds a ring,are are calledcalled cycloalkanes. . Alkanes lack functional groups; as a result, they are relatively nonpolar and unreactive. The They arepropertiesrelatively andnonpolar chemistry andof theunreactive alkanes are. described in this chapter and in Chapters 3 and 4. Cycloalkanes Alkanes H2 CH4 CH3OOCH3 CH3 CH2OCH3 CH3OCH2OCH2OCH3 C Methane Ethane Propane Butane 2 H2C CH2

Double and triple bonds are the functional groups of alkenes and alkynes, respectively. H2C CH2 Their properties and chemistry are the topics of Chapters 11 through 13. Cyclopentane

Alkenes and Alkynes H2 H C i CH2PCH2 CPCH2 HCq CH CH3OCqCH H2C CH2 f CH 3 H2C CH2 Ethene Propene Ethyne Propyne C (Ethylene) (Acetylene) H2 Cyclohexane A special hydrocarbon is benzene, C6H6, in which three double bonds are incorporated into a six-membered ring. Benzene and its derivatives are traditionally called aromatic, because some substituted benzenes do have a strong fragrance. Aromatic compounds, also called arenes, are discussed in Chapters 15, 16, 22, and 25.

Aromatic Compounds (Arenes)

H CH3 HHC HHC C C C C C C C C H C H H C H H H Benzene Methylbenzene (Toluene) 2-4 Functional Groups: Centers of Reactivity CHAPTER 2 69

by an acid dissociation constant Ka. Removal of a proton from an acid generates its conjugate base; attachment of a proton to a base forms its conjugate acid. Lewis bases donate 2-4 Functional Groups: Centers of Reactivity CHAPTER 2 69 an electron pair to form a covalent bond with Lewis acids, a process depicted by a curved arrow pointing from the lone pair of the base toward the acid. Electrophiles and nucleophiles are species in organic chemistry that interact very much like acids and bases. The by an acid dissociation constant Ka. Removal of a proton from an acid generates its conju- carbon–halogen bond in the haloalkane is its functional group. It contains an electrophilicgate base; attachment of a proton to a base forms its conjugate acid. Lewis bases donate carbon atom, which reacts with nucleophiles in a process called nucleophilic substitution.an electron pair to form a covalent bond with Lewis acids, a process depicted by a curved arrow pointing from the lone pair of the base toward the acid. Electrophiles and nucleophiles are species in organic chemistry that interact very much like acids and bases. The carbon–halogen bond in the haloalkane is its functional group. It contains an electrophilic 2-4 FUNCTIONAL GROUPS: CENTERS OF REACTIVITY carbon atom, which reacts with nucleophiles in a process called nucleophilic substitution.

Many organic molecules consist predominantly of a backbone of carbons linked by single bonds, with only hydrogen atoms attached. However, they may also contain doubly or R Function triply bonded carbons, as well as other elements. These atoms or groups of atoms 2-4tend to FUNCTIONAL GROUPS: CENTERS OF REACTIVITY be sites of comparatively high chemical reactivity and are referred to as functional groups or functionalities. Such groups have characteristic properties, and they control the reactiv- Many organic Carbonmolecules frame consist predominantlyFunctional of a backbone of carbons linked by single R Function ity of the molecule as a whole. bonds, with onlyprovides hydrogen atomsgroup attached. imparts However, they may also contain doubly or triply bonded carbons,structure as well as reactivityother elements. These atoms or groups of atoms tend to Hydrocarbons are molecules that contain only be sites of comparatively high chemical reactivity and are referred to as functional groups or functionalities. Such groups have characteristic properties, and they control the reactiv- hydrogen and carbon Carbon frame Functional ity of the molecule as a whole. We begin our study with hydrocarbons, which have the general empirical formula CxHy. provides group imparts Those containing only single bonds, such as methane, ethane, and propane, are called structure reactivity alkanes. Molecules such as cyclohexane, whose carbons form a ring, are called cycloalkanes. Hydrocarbons are molecules that contain only Alkanes lack functional groups; as a result, they are relatively nonpolar and Molecules unreactive.hydrogen The such andas cyclohexane, carbon whose carbons form a ring, are called cycloalkanes. properties and chemistry of the alkanes are described in this chapter and in ChaptersWe 3 and begin 4. our study with hydrocarbons, which have the general empirical formula CxHy. Those containing only Cycloalkanes single bonds, such as methane, ethane, and propane, are called Alkanes alkanes. Molecules such as cyclohexane, whose carbons form a ring, are called cycloalkanes. H2 CH4 CH3OOCH3 CH3 CH2OCH3 CH3OCH2OCH2OCHAlkanes3 lack functional groups;C as a result, they are relatively nonpolar and unreactive. The Methane Ethane Propane Butane properties and chemistry of the alkanes are described in this chapter and in Chapters 3 and 4. H2C CH2 Cycloalkanes Double and triple bonds are the functional groups of alkenes and alkynes, respectively. H2C CH2 Alkanes Their properties and chemistry are the topics of Chapters 11 through 13. Cyclopentane H2 CH4 CH3OOCH3 CH3 CH2OCH3 CH3OCH2OCH2OCH3 C Methane Ethane Propane Butane Alkenes and Alkynes H2C CH2 H2 H C CH H DoubleDoubleand andtriple triplebonds bonds are are the theC functionalfunctional groupsgroups of alkenesof alkenes and alkynes,and alkynes, respectively.respectively . 2 2 i Their properties and chemistry are the topics of Chapters 11 through 13. Cyclopentane CH2PCH2 CPCH2 HCq CH CH3OCqCH H2C CH2 f CH3 H C AlkenesCH and Alkynes 2 2 H Ethene Propene Ethyne Propyne CH 2 (Ethylene) (Acetylene) H2 C i H C CH CH2PCH2 CyclohexaneCPCH2 HCq CH CH3OCqCH 2 2 f A special hydrocarbon is benzene, C6H6, in which three double bonds are incorporated CH 3 H2C CH2 into a six-membered ring. Benzene and its derivatives are traditionally called aromatic, Ethene Propene Ethyne Propyne C because some substituted benzenes do have a strong fragrance. Aromatic compounds, also (Ethylene) (Acetylene) H2 called arenes, are discussed in Chapters 15, 16, 22, and 25. Cyclohexane 3 A special hydrocarbon is benzene, C6H6, in which three double bonds are incorporated Aromatic Compounds (Arenes) into a six-membered ring. Benzene and its derivatives are traditionally called aromatic, because some substituted benzenes do have a strong fragrance. Aromatic compounds, also H CH3 called arenes, are discussed in Chapters 15, 16, 22, and 25. HHC HHC C C C C Aromatic Compounds (Arenes)

C C C C H CH3 H C H H C H HHC HHC H H C C C C Benzene Methylbenzene C C C C (Toluene) H C H H C H H H Benzene Methylbenzene (Toluene) 2-4 Functional Groups: Centers of Reactivity CHAPTER 2 69

2-4 FUNCTIONAL GROUPS: CENTERS OF REACTIVITY

We begin our study with hydrocarbons, which have the general empirical formula CxHy. Those containing only single bonds, such as methane, ethane, and propane, are called alkanes. Molecules such as cyclohexane, whose carbons form a ring, are called cycloalkanes. Alkanes lack functional groups; as a result, they are relatively nonpolar and unreactive. The properties and chemistry of the alkanes are described in this chapter and in Chapters 3 and 4. Cycloalkanes Alkanes H2 CH4 CH3OOCH3 CH3 CH2OCH3 CH3OCH2OCH2OCH3 C Methane Ethane Propane Butane H2C CH2

Double and triple bonds are the functional groups of alkenes and alkynes, respectively. H2C CH2 Their properties and chemistry are the topics of Chapters 11 through 13. Cyclopentane

Alkenes and Alkynes H2 H C i CH2PCH2 CPCH2 HCq CH CH3OCqCH H2C CH2 f CH 3 H2C CH2 Ethene Propene Ethyne Propyne C (Ethylene) (Acetylene) H Benzene, C H , in which three double bonds are incorporated into a six-membered ring. 2 6 6 Cyclohexane A special hydrocarbon is benzene, C6H6, in which three double bonds are incorporated Benzene andinto aits six-memberedderivatives ring.are Benzenetraditionally and its called derivativesaromatic, are traditionallybecause calledsome aromatic,substituted benzenesbecausedo have somea strongsubstitutedfragrance benzenes. do have a strong fragrance. Aromatic compounds, also called arenes, are discussed in Chapters 15, 16, 22, and 25.

Aromatic Compounds (Arenes)

H CH3 HHC HHC C C C C C C C C H C H H C H H H Benzene Methylbenzene (Toluene)

4 70 CHAPTER 2 Structure and Reactivity

Table 2-3 Common Functional Groups Compound class General structurea Functional group Example

Alkanes ROH None CH3CH2CH2CH3 (Chapters 3, 4) Butane

Haloalkanes RO"šXð(X ϭ F, Cl, Br, I) O"šXð CH3CH2 OBr"šð (Chapters 6, 7) Bromoethane H A Alcohols ROHO"š O"šOH (CH3)2CO"šOH (Chapters 8, 9) 2-Propanol (Isopropyl alcohol)

Ethers ROO"šORЈ OO"šO CH3CH2 OO"šO CH3 (Chapter 9) Methoxyethane R represents a (Ethyl methyl ether) part of an alkane Thiols RSHO"š O"šSH CH3CH2O"šSH molecule (Chapter 9) Ethanethiol

(H)R R(H) CH3 i i i i i Alkenes CPC CPC CPCH2 (Chapters 11, 12) f f f f f (H)R R(H) CH3 2-Methylpropene

Alkynes (H)ROOCCq R(H) OOCCq CH3CCq CH3 (Chapter 13) 2-Butyne

R(H) CH3 (H)R C R(H) C C C C C C HCCH Aromatic compounds (Chapters 15, 16, 22) C C C C HC CH (H)R C R(H) C C H R(H) Methylbenzene 5 (Toluene) ðOð Oðð Oðð B B B Aldehydes RCOOH OCOH CH3CH2CH (Chapters 17, 18) Propanal Oðð Oðð Oðð B B B Ketones RCOORЈ OOC CH3CH2CCH2CH2CH3 (Chapters 17, 18) 3-Hexanone Oðð Oðð Oðð B B B š š Carboxylic acids RCOOO"šOH OCO"OH CH3CH2COH" (Chapters 19, 20) Propanoic acid ððOð ðO ððOð ððO Oððð O B B B B B B š š Anhydrides RCO O"OROOC Ј(H) OCO"OOCO CH3CH2COC"š CH2CH3 (Chapters 19, 20) Propanoic anhydride Oðð Oðð Oðð B B B Esters (H)ROO C "šOORЈ OCO"šOO CH3CH2CO"šCH3 (Chapters 19, 20, 23) Methyl propanoate aThe letter R denotes an alkyl group (see text). Different alkyl groups can be distinguished by (Methyl propionate) adding primes to the letter R: R9, R0, and so forth. 70 CHAPTER 2 Structure and Reactivity

Table 2-3 Common Functional Groups Compound class General structurea Functional group Example

Alkanes ROH None CH3CH2CH2CH3 (Chapters 3, 4) Butane

Haloalkanes RO"šXð(X ϭ F, Cl, Br, I) O"šXð CH3CH2 OBr"šð (Chapters 6, 7) Bromoethane H A Alcohols ROHO"š O"šOH (CH3)2CO"šOH (Chapters 8, 9) 2-Propanol (Isopropyl alcohol)

Ethers ROO"šORЈ OO"šO CH3CH2 OO"šO CH3 (Chapter 9) Methoxyethane (Ethyl methyl ether)

Thiols RSHO"š O"šSH CH3CH2O"šSH (Chapter 9) Ethanethiol

(H)R R(H) CH3 i i i i i Alkenes CPC CPC CPCH2 (Chapters 11, 12) f f f f f (H)R R(H) CH3 2-Methylpropene

Alkynes (H)ROOCCq R(H) OOCCq CH3CCq CH3 (Chapter 13) 2-Butyne

R(H) CH3 (H)R C R(H) C C C C C C HCCH Aromatic compounds (Chapters 15, 16, 22) C C C C HC CH (H)R C R(H) C C H R(H) Methylbenzene (Toluene) ðOð Oðð Oðð B B B Aldehydes RCOOH OCOH CH3CH2CH (Chapters 17, 18) Propanal Oðð Oðð Oðð B B B Ketones RCOORЈ OOC CH3CH2CCH2CH2CH3 (Chapters 17, 18) 3-Hexanone Oðð Oðð Oðð B B B š š Carboxylic acids RCOOO"šOH OCO"OH CH3CH2COH" (Chapters 19, 20) Propanoic acid ððOð ðO ððOð ððO Oððð O B B B B B B š š Anhydrides RCO O"OROOC Ј(H) OCO"OOCO CH3CH2COC"š CH2CH3 (Chapters 19, 20) Propanoic anhydride 2-4 Functional Groups: Centers of Reactivity CHAPTER 2 71 Oðð Oðð Oðð B B B Esters (H)ROO C "šOORЈ OCO"šOO CH3CH2CO"šCH3 (Chapters 19, 20, 23) Methyl propanoate TableaThe letter 2-3 R denotes(continued) an alkyl group (see text). Different alkyl groups can be distinguished by (Methyl propionate) Compoundadding primes classto the letter R: R9, R0, and so forth.General structure Functional group Example

Oðð Oðð Oðð B B B f Amides RCO OšNORЈ(H) OCOšN CH3CH2CH2CNšH2 (Chapters 19, 20, 26) A i Butanamide RЉ(H)

Nitriles RCNO q ð OCNq ð CH3CqNð (Chapter 20) Ethanenitrile (Acetonitrile) f Amines RNOOšORЈ(H) šN (CH3)3Nð (Chapter 21) A i N,N-Dimethylmethanamine 6 RЉ(H) (Trimethylamine)

Many functional groups contain polar bonds Polar bonds determine the behavior of many classes of molecules. Recall that polarity is due to a difference in the electronegativity of two atoms bound to each other (Section 1-3). We have already introduced the haloalkanes, which contain polar carbon – halogen bonds as their functional groups. In Chapters 6 and 7 we shall explore their chemistry in depth. Another functionality is the hydroxy group, – O – H, characteristic of alcohols. The characteristic functional unit of ethers is an oxygen bonded to two carbon atoms ƒ ƒ (OCOOOCO). The functional group in alcohols and in some ethers can be converted into ƒ ƒ a large variety of other functionalities and are therefore important in synthetic transforma- tions. This chemistry is the subject of Chapters 8 and 9.

Haloalkanes Alcohols Ethers ...... CH3Cl..: CH3CH2Cl..: CH3..OH CH3CH2..OH CH3..OCH3 CH3CH2..OCH2CH3 Chloromethane Chloroethane Methanol Ethanol Methoxymethane Ethoxyethane (Methyl chloride) (Ethyl chloride) (Dimethyl ether) (Diethyl ether) (Topical anesthetics) (Wood alcohol) (Grain alcohol) (A refrigerant) (An inhalation anesthetic)

The carbonyl functional group, C=O, is found in aldehydes, in ketones, and, in conjunction with an attached 2OH, in the carboxylic acids. Aldehydes and ketones are discussed in Chapters 17 and 18, the carboxylic acids and their derivatives in Chapters 19 and 20.

Aldehydes Ketones Carboxylic Acids Oðð Oðð Oðð Oðð Oðð B B B B B HCH CH3CH or CH3CHO CH3CCH3 CH3CH2CCH3 HCOH"š or HCOOH Formaldehyde Acetaldehyde Acetone Butanone or HCO2H (Methyl ethyl ketone) Formic acid (A disinfectant) (A hypnotic) (Common solvents) (Strong irritant)

Oðð B CH3COH"š or CH3 COOH or CH3CO2H Acetic acid (In vinegar) 72 CHAPTER 2 Structure and Reactivity

Other elements give rise to further characteristic functional groups. For example, alkyl nitrogen compounds are amines. The replacement of oxygen in alcohols by sulfur furnishes thiols.

Amines A Thiol H A CH3NHš 2 CH3!NCH3 or (CH3)2šNH CH3!šSH Methanamine N-Methylmethanamine Methanethiol (Methylamine) (Dimethylamine) (Used in tanning leather) (Excreted after we eat asparagus)

R represents a part of an alkane molecule Table 2-3 depicts a selection of common functional groups, the class of compounds to which they give rise, a general structure, and an example. In the general structures, we commonly use the symbol R (for radical or residue) to represent an alkyl group, a molecular fragment derived by removal of one hydrogen atom from an alkane (Section 2-6). Therefore, a general formula for a haloalkane is R–X, in which R stands for any alkyl group and X for any halogen. Alcohols are similarly represented as R–O–H. In structures that contain multiple alkyl groups, we add a prime (9) or double prime (0) to R to distinguish groups that differ in structure from one another. Thus a general formula for an ether in which both alkyl groups are the same (a symmetrical ether) is R–O–R, whereas an ether with two dis- similar groups (an unsymmetrical ether) is represented by R–O–R9.

2-5 STRAIGHT-CHAIN AND BRANCHED ALKANES

The functional groups in organic molecules are typically attached to a hydrocarbon scaffold Alkanes constructed only with single bonds. Substances consisting entirely of single-bonded carbon and hydrogen atoms and lacking functional groups are called alkanes. They are classi! ed Substances consisting intoentirely severalof typessingle according-bonded to structure:carbon the andlinear hydrogenstraight-chainatoms alkanes;and the lackingbranched functional groups. alkanes, in which the carbon chain contains one or several branching points; and the cyclic They are classified: linearalkanes,straight or cycloalkanes,-chain alkaneswhich we ;shallthe coverbranched in Chapteralkanes, 4. cyclic alkanes (cycloalkanes) Model Building A Straight-Chain Alkane A Branched Alkane A Cycloalkane

CH3 A CH3OCH2OCH2OOCH3 CH3 COH CH2OCH2 AAA CH3 CH2OCH2

Butane, C4H10 2-Methylpropane, C4H10 Cyclobutane, C4H8 (Isobutane)

Straight-chain alkanes form a homologous series In the straight-chain alkanes,Straight-chaineach carbon alkanesis formbound a homologousto its two neighbors series and to two

hydrogen atoms, with generalIn the straight-chainformula: Halkanes,–(CH 2each)n–H carbon. is bound to its two neighbors and to two hydrogen atoms. Exceptions are the two terminal carbon nuclei, which are bound to only one Each member of this seriescarbon differsatom andfrom three thehydrogennext atoms.lower Theone straight-chainby the addition alkane seriesof a maymethylene be described by the general formula H–(CH2)n–H. Each member of this series differs from the next lower group, –CH2–. Molecules that are related in this way are homologs of each other (homos, one by the addition of a methylene group, –CH2–. Molecules that are related in this way Greek, same as), and theare homologsseries is ofa eachhomologous other (homos, seriesGreek, same. as), and the series is a homologous series. Methane (n 5 1) is the ! rst member of the homologous series of the alkanes, ethane (n 5 72) the second, and so forth. Branched alkanes are constitutional isomers2-6 Namingof straight the Alkanes-chain CHAPTERalkanes 2 73 Branched alkanes are derived from the straight-chain systems by removal of a hydrogen

from a methylene (CH2) group and replacement with an alkyl group. Both branched and Branchedstraight- chainalkanesalkanes are constitutionalhave the same isomersgeneral formula, CnH2n+2. Number of of straight-chain alkanes Table 2-4 Possible Isomeric Alkanes, C H BranchedThe smallest alkanes are branched derived from alkane the straight-chainis 2-methylpropane systems by removal. ofIt ahas hydrogenthe same molecular formulan 2n 12 as 2-6 Naming the Alkanes CHAPTER 2 73 from a methylene (CH2) group and replacement with an alkyl group. Both branched and n Isomers that of butane (C4H10) but different connectivity; the two compounds therefore form a pair of straight-chain alkanes have the same general formula, CnH2n12. The smallest branched alkaneconstitutional is 2-methylpropane.isomers It has. the same molecular formula as that of butane (C4H10) but 1 1 different connectivity; the two compounds therefore form a pair of constitutional isomers 2 1 Branched alkanes are constitutional isomers Number of (Section 1-9). 3 1 of straight-chain alkanes Table 4 2-4 Possible Isomeric 2 ForThe thenumber higher alkaneof possibilitieshomologs (n . in4), connectingmore than two nisomerscarbon are possible.atoms toThereeach are Branched alkanes are derived from the straight-chain systems by removal of a hydrogen 5 Alkanes, Cn H2n 12 3 threeother pentanes,and C5H12,to as shown2n+2 below.surrounding There are ! ve hexanes,hydrogen C6H14;atoms nine heptanes,increases C7H16; 6 5 from a methylene (CH2) group and replacement with an alkyl group. Both branched and n Isomers and eighteen octanes, C8H18. straight-chaindramatically alkaneswith the have size the sameof n . general formula, CnH2n12. The smallest branched 7 9 alkane is 2-methylpropane. It has the same molecular formula as that of butane (C4H10) but 1 8 1 18 different connectivity; the two compounds therefore form a pair of constitutional isomers 2 9 1 35 (Section 1-9). The Isomeric Pentanes 310 1 75 4 2 For the higher alkane homologs (n . 4), more than two isomers are possible. There are 15 4,347 CH3 CH3 520 366,3193 three pentanes, C5H12, as shown below. There are ! ve hexanes,A C6H14; nine heptanes,A C7H16; 6 5 andCH eighteen3OOCH 2octanes,CH2OO CCH8H182. CH3 CH3O 2OCHCH CH3OCOCH3 A A 7 9 CH CH 8 18 3 3 9 35 Pentane The Isomeric2-Methylbutane Pentanes 2,2-Dimethylpropane 10 75 (Isopentane) (Neopentane) 15 4,347 CH3 CH3 8 A A 20 366,319 CH3OOCH2 CH2OOCH2 CH3 CH3O 2OCHCH CH3OCOCH3 The number of possibilities in connecting n carbon atoms Ato each other andA to 2n 1 2 sur- Model Building rounding hydrogen atoms increases dramatically with the CHsize3 of n (Table 2-4).CH3 Pentane 2-Methylbutane 2,2-Dimethylpropane (Isopentane) (Neopentane)

Exercise 2-16 The number of possibilities in connecting n carbon atoms to each other and to 2n 1 2 sur- Model Building (a)rounding Draw the hydrogen structures atoms of the increases ! ve isomeric dramatically hexanes. with(b) Draw the size the structuresof n (Table of 2-4).all the possible next higher and lower homologs of 2-methylbutane.

Exercise 2-16 2-6(a) DrawNAMING the structures THE of the ALKANES ! ve isomeric hexanes. (b) Draw the structures of all the possible next higher and lower homologs of 2-methylbutane. The multiple ways of assembling carbon atoms and attaching various substituents accounts for the existence of the very large number of organic molecules. This diversity poses a problem:2-6 How NAMING can we systematically THE ALKANES differentiate all these compounds by name? Is it possible, for example, to name all the C6H14 isomers so that information on any of them (such as boiling points, melting points, reactions) might easily be found in the index of a handbook The multiple ways of assembling carbon atoms and attaching various substituents accounts or in an online database? And is there a way to name a compound that we have never seen for the existence of the very large number of organic molecules. This diversity poses a in such a way as to be able to draw its structure? problem: How can we systematically differentiate all these compounds by name? Is it pos- This problem of naming organic molecules has been with organic chemistry from its very sible, for example, to name all the C6H14 isomers so that information on any of them (such beginning,as boiling but points, the initial melting method points, was reactions) far from might systematic. easily beCompounds found in the have index been of anamed handbook after theiror discoverers in an online (“Nenitzescu’s database? And hydrocarbon”), is there a way afterto name localities a compound (“sydnones”), that we afterhave theirnever shapes seen (“cubane,”in such “basketane”),a way as to be and able after to drawtheir itsnatural structure? sources (“vanillin”). Many of these common or trivialThis names problem are ofstill naming widely organic used. moleculesHowever, has there been now with exists organic a precise chemistry system from for its verynam- ing thebeginning, alkanes. but Systematic the initial method nomenclature, was far from in whichsystematic. the nameCompounds of a compound have been describesnamed after its structure,their discoverers was ! rst introduced (“Nenitzescu’s by a hydrocarbon”), chemical congress after localitiesin Geneva, (“sydnones”), Switzerland, after in their1892. shapes It has continually(“cubane,” been “basketane”), revised since and then,after mostlytheir natural by the sources International (“vanillin”). Union Many of ofPure these and common Applied Chemistryor trivial (IUPAC). names are Table still widely 2-5 gives used. the However, systematic there names now exists of the a precise ! rst 20 system straight-chain for nam- alkanes.ing the Their alkanes. stems, Systematic mainly of nomenclature,Greek origin, revealin which the thenumber name of of carbon a compound atoms describesin the chain. its For structure,example, wasthe name! rst introduced heptadecane by a is chemical composed congress of the in Greek Geneva, words Switzerland, hepta, seven, in 1892. and It deka, has ten. continuallyThe ! rst four been alkanes revised have since special then, namesmostly that by thehave International been accepted Union as partof Pure of the and sys Appliedtematic Chemistry (IUPAC). Table 2-5 gives the systematic names of the ! rst 20 straight-chain alkanes. Their stems, mainly of Greek origin, reveal the number of carbon atoms in the chain. For example, the name heptadecane is composed of the Greek words hepta, seven, and deka, ten. The ! rst four alkanes have special names that have been accepted as part of the systematic 74 CHAPTER 2 Structure and Reactivity

Table 2-5 Names and Physical Properties of Straight-Chain Alkanes, CnH2n12 Boiling Melting point point Density at 208C n Name Formula (8C) (8C) (g mL21)

1 Methane CH4 2161.7 2182.5 0.466 (at 21648C) 2 Ethane CH3CH3 288.6 2183.3 0.572 (at 21008C) 3 Propane CH3CH2CH3 242.1 2187.7 0.5853 (at 2458C) 4 Butane CH3CH2CH2CH3 20.5 2138.3 0.5787 5 Pentane CH3(CH2)3CH3 36.1 2129.8 0.6262 6 Hexane CH3(CH2)4CH3 68.7 295.3 0.6603 7 Heptane CH3(CH2)5CH3 98.4 290.6 0.6837 8 Octane CH3(CH2)6CH3 125.7 256.8 0.7026 9 Nonane CH3(CH2)7CH3 150.8 253.5 0.7177 10 Decane CH3(CH2)8CH3 174.0 229.7 0.7299 11 Undecane CH3(CH2)9CH3 195.8 225.6 0.7402 12 Dodecane CH3(CH2)10CH3 216.3 29.6 0.7487 Propane stored under pressure in 13 Tridecane CH3(CH2)11CH3 235.4 25.5 0.7564 lique! ed form in canisters such 14 Tetradecane CH3(CH2)12CH3 253.7 5.9 0.7628 Common or trivial names: compounds have been namedas theseafter is a commontheir discoverersfuel for 15 Pentadecane CH (CH ) CH 270.6 10 0.7685 torches, lanterns, and outdoor 3 2 13 3 (“Nenitzescu’s hydrocarbon”), after localities (“sydnones”), cookingafter their stoves.shapes (“cubane,” 16 Hexadecane CH3(CH2)14CH3 287 18.2 0.7733 “basketane”), and after their natural sources (“vanillin”). [Courtesy Bernzomtic, Columbus, OH.] 17 Heptadecane CH3(CH2)15CH3 301.8 22 0.7780 18 Octadecane CH3(CH2)16CH3 316.1 28.2 0.7768 19 Nonadecane CH (CH ) CH 329.7 32.1 0.7855 Systematic nomenclature: the name of a compound describes its structure, introduced by 3 2 17 3 20 Icosane CH3(CH2)18CH3 343 36.8 0.7886 the International Union of Pure and Applied Chemistry (IUPAC).

In systematic nomenclature, the names all end in -ane. CH3 A nomenclature but also all end in -ane. It is important to know these names, because they serve CH3OCO(CH2)nOCH3 A as the basis for naming a large fraction of all organic molecules. A few smaller branched H A few smaller branched alkanes have common names that alkanes have common names that still have widespread use. They make use of the pre! xes An isoalkane iso- and neo- (margin), as in isobutane, isopentane, and neohexane. (isopentane ,1 ؍ still have widespread use. (e.g., n

CH3 They make use of the prefixes iso- and neo- (margin), as A in isobutane, isopentane, and neohexene. CH3OCO(CH2)nOH A Exercise 2-17 CH3 A neoalkane Draw the structures of isohexane and neopentane. (neohexane ,2 ؍ e.g., n) 9

Alkyl groups As mentioned in Section 2-5, an alkyl group is formed by the removal of a hydrogen from an alkane. It is named by replacing the ending -ane in the corresponding alkane by CH — 3 -yl, as in methyl, ethyl, and propyl. Table 2-6 shows a few branched alkyl groups having Methyl common names. Note that some have the pre! xes sec- (or s-), which stands for secondary, and tert- (or t-), for tertiary. These pre! xes are used to classify sp3-hybridized CH3 — CH2 — (tetrahedral) carbon atoms in organic molecules. A primary carbon is one attached Ethyl directly to only one other carbon atom. For example, all carbon atoms at the ends of alkane chains are primary. The hydrogens attached to such carbons are designated pri- CH3 — CH2 — CH2 — mary hydrogens, and an alkyl group created by removing a primary hydrogen also is Propyl called primary. A secondary carbon is attached directly to two other carbon atoms, and a tertiary carbon to three others. Their hydrogens are labeled similarly. As shown in Table 2-6, removal of a secondary hydrogen results in a secondary alkyl group, and removal of a tertiary hydrogen in a tertiary alkyl group. Finally, a carbon bearing four alkyl groups is called quaternary. 74 CHAPTER 2 Structure and Reactivity

Table 2-5 Names and Physical Properties of Straight-Chain Alkanes, CnH2n12 Boiling Melting point point Density at 208C n Name Formula (8C) (8C) (g mL21)

1 Methane CH4 2161.7 2182.5 0.466 (at 21648C) 2 Ethane CH3CH3 288.6 2183.3 0.572 (at 21008C) 3 Propane CH3CH2CH3 242.1 2187.7 0.5853 (at 2458C) 4 Butane CH3CH2CH2CH3 20.5 2138.3 0.5787 5 Pentane CH3(CH2)3CH3 36.1 2129.8 0.6262 6 Hexane CH3(CH2)4CH3 68.7 295.3 0.6603 7 Heptane CH3(CH2)5CH3 98.4 290.6 0.6837 8 Octane CH3(CH2)6CH3 125.7 256.8 0.7026 9 Nonane CH3(CH2)7CH3 150.8 253.5 0.7177 10 Decane CH3(CH2)8CH3 174.0 229.7 0.7299 11 Undecane CH3(CH2)9CH3 195.8 225.6 0.7402 12 Dodecane CH3(CH2)10CH3 216.3 29.6 0.7487 Propane stored under pressure in 13 Tridecane CH3(CH2)11CH3 235.4 25.5 0.7564 lique! ed form in canisters such 14 Tetradecane CH3(CH2)12CH3 253.7 5.9 0.7628 as these is a common fuel for 15 Pentadecane CH (CH ) CH 270.6 10 0.7685 torches, lanterns, and outdoor 3 2 13 3 cooking stoves. 16 Hexadecane CH3(CH2)14CH3 287 18.2 0.7733 [Courtesy Bernzomtic, Columbus, OH.] 17 Heptadecane CH3(CH2)15CH3 301.8 22 0.7780 18 Octadecane CH3(CH2)16CH3 316.1 28.2 0.7768 19 Nonadecane CH3(CH2)17CH3 329.7 32.1 0.7855 20 Icosane CH3(CH2)18CH3 343 36.8 0.7886

CH3 A nomenclature but also all end in -ane. It is important to know these names, because they serve CH3OCO(CH2)nOCH3 A as the basis for naming a large fraction of all organic molecules. A few smaller branched H alkanes have common names that still have widespread use. They make use of the pre! xes An isoalkane iso- and neo- (margin), as in isobutane, isopentane, and neohexane. (isopentane ,1 ؍ e.g., n)

CH3 A CHAn3OalkylCO(CHgroup2)nOHis formed by the removal of a hydrogen from an alkane. It is named by A Exercise 2-17 replacingCH3 the ending -ane in the corresponding alkane by -yl, as in methyl, ethyl, and propylA neoalkane. Draw the structures of isohexane and neopentane. neohexane) 2-6 Naming the Alkanes CHAPTER 2 75 ,2 ؍ e.g., n) The prefixes sec- (or s-) stands for secondary, and tert- (or t-) for tertiary.

Table 2-6 Branched Alkyl Groups Structure Common name Example of common name in use Systematic name Type of group Alkyl groups As mentioned in Section 2-5, an alkyl group is formed by the removal of a hydrogen CH3 CH3 fromA an alkane. It is named by Areplacing the ending -ane in the corresponding alkane by CH3 — 3 OOCCH Isopropyl CH3 OOC Cl (Isopropyl chloride) 1-Methylethyl Secondary -yl,A as in methyl, ethyl, and propyl.A Table 2-6 shows a few branched alkyl groups having Methyl commonH names. Note that someH have the pre! xes sec- (or s-), which stands for second- 3 ary,CH3 and tert- (or t-), for tertiary.CH3 These pre! xes are used to classify sp -hybridized CH —CH — A A 3 2 3 OO(tetrahedral)CCH CH2 O carbon Isobutyl atoms 3 inOO CCH organicCH3 (Isobutane) molecules. A primary2-Methyl propylcarbon is Primary one attached A A Ethyl directlyH to only one other carbonH atom. For example, all carbon atoms at the ends of

alkaneCH 3chains are primary. The hydrogensCH3 attached to such carbons are designated pri- A A CH3 — CH2 — CH2 — CH3 OOmary2 OCCH hydrogens, sec-Butyl and an alkylCH3 OO group2 OCCH NH created2 (sec-Butyl by amine) removing 1-Methyl a primarypropyl hydrogen Secondary also is A A Propyl calledH primary. A secondary carbonH is attached directly to two other carbon atoms, and

aCH tertiary3 carbon to three others.CH3 Their hydrogens are labeled similarly. As shown in TableA 2-6, removal of a secondaryA hydrogen results in a secondary alkyl group, and 3 OOCCH tert-Butyl CH3 OOC Br (tert-Butyl bromide) 1,1-Dimethylethyl Tertiary removalA of a tertiary hydrogenA in a tertiary alkyl group. Finally, a carbon bearing four CH3 CH3 alkyl groups is called quaternary. CH3 CH3 A A 3 OOCCH CH2 O Neopentyl CH3OOCCH2 O OH (Neopentyl alcohol) 2,2-Dimethylpropyl Primary A A CH3 CH3 10

Primary, Secondary, and Tertiary Carbons and Hydrogens

Primary C

CH3 Secondary C A Tertiary C CH3CH2CCH2CH3 Primary H A H Secondary H Tertiary H 3-Methylpentane The terms primary, secondary, tertiary, and quaternary are reserved for carbon atoms Exercise 2-18 with exclusively single bonds. Label the primary, secondary, and tertiary hydrogens in 2-methylpentane (isohexane). They are not applied to carbon atoms with double or triple bonds. The information in Table 2-5 enables us to name the ! rst 20 straight-chain alkanes. How do we go about naming branched systems? A set of IUPAC rules makes this a relatively simple task, as long as they are followed carefully and in sequence.

IUPAC Rule 1. Find the longest chain in the molecule and name it. This task is not as easy as it seems. The problem is that, in the condensed formula, complex alkanes may be written in ways that mask the identity of the longest chain. Do not assume that it is always depicted horizontally! In the following examples, the longest chain, or stem chain, is clearly The stem chain is shown in marked; the alkane stem gives the molecule its name. Groups other than hydrogen attached black in the examples in this to the stem chain are called substituents. section.

Methyl CH3 CH3CH2 CH2CH2CH2CH3 A A A Ethyl CH3CHCH2CH3 CH3CHCH2CH2CHCH2CH3 A methyl-substituted butane An ethyl- and methyl-substituteddecane (A methylbutane) (An ethylmethyldecane) 2-6 Naming the Alkanes CHAPTER 2 75

Table 2-6 Branched Alkyl Groups Structure Common name Example of common name in use Systematic name Type of group

CH3 CH3 A A 3 OOCCH Isopropyl CH3 OOC Cl (Isopropyl chloride) 1-Methylethyl Secondary A A H H

CH3 CH3 A A 3 OOCCH CH2 O Isobutyl 3 OOCCH CH3 (Isobutane) 2-Methylpropyl Primary A A H H

CH3 CH3 A A CH3 OO2 OCCH sec-Butyl CH3 OO2 OCCH NH2 (sec-Butyl amine) 1-Methylpropyl Secondary A A H H

A primary carbonCHis 3one attached directly to only oneCHother3 carbon atom. A A 3 OOCCH tert-Butyl CH3 OOC Br (tert-Butyl bromide) 1,1-Dimethylethyl Tertiary A secondary carbonA is attached directly to two otherA carbon atoms, and a tertiary carbon CH to three others. CH3 3 CH3 CH3 A A A carbon bearing3 OOfourCCH CHalkyl2 O groups Neopentylis called quaternaryCH3OOCCH. 2 O OH (Neopentyl alcohol) 2,2-Dimethylpropyl Primary A A CH3 CH3

Primary, Secondary, and Tertiary Carbons and Hydrogens

Primary C

CH3 Secondary C A Tertiary C CH3CH2CCH2CH3 Primary H A H Secondary H Tertiary H 3-Methylpentane The terms primary, secondary, tertiary, and quaternary are reserved for carbon atoms Exercise 2-18 with11 exclusively single bonds. Label the primary, secondary, and tertiary hydrogens in 2-methylpentane (isohexane). They are not applied to carbon atoms with double or triple bonds. The information in Table 2-5 enables us to name the ! rst 20 straight-chain alkanes. How do we go about naming branched systems? A set of IUPAC rules makes this a relatively simple task, as long as they are followed carefully and in sequence.

Table 2-6 Branched Alkyl Groups Structure Common name Example of common name in use Systematic name Type of group

CH3 CH3 A A 3 OOCCH Isopropyl CH3 OOC Cl (Isopropyl chloride) 1-Methylethyl Secondary A A H H

CH3 CH3 A A 3 OOCCH CH2 O Isobutyl 3 OOCCH CH3 (Isobutane) 2-Methylpropyl Primary A A H H

CH3 CH3 A A CH3 OO2 OCCH sec-Butyl CH3 OO2 OCCH NH2 (sec-Butyl amine) 1-Methylpropyl Secondary A A H H

CH3 CH3 A A 3 OOCCH tert-Butyl CH3 OOC Br (tert-Butyl bromide) 1,1-Dimethylethyl Tertiary A A CH3 CH3

CH3 CH3 A A 3 OOCCH CH2 O Neopentyl CH3OOCCH2 O OH (Neopentyl alcohol) 2,2-Dimethylpropyl Primary A A CH3 CH3

Primary, Secondary, and Tertiary Carbons and Hydrogens

Primary C

IUPAC Rule 1. Find the longest chain in the molecule and name it. This task is not as easy as it seems. The problem is that, in the condensed formula, complex alkanes may be NAMING THE ALKANES written in ways that mask the identity of the longest chain. Do not assume that it is always IUPAC Rule 1. Find the longestdepictedchain horizontally!in the moleculeIn the followingand nameexamples,it. the longest chain, or stem chain, is clearly The stem chain is shown in The longest chain, or stemmarked;chain, the isalkaneclearly stemmarked gives the; the moleculealkane itsstem name.gives Groupsthe othermolecule than hydrogenits attached black in the examples in this name. Groups other thantohydrogen the stem chainattached are calledto the substituents.stem chain are called substituents. section.

Methyl CH3 CH3CH2 CH2CH2CH2CH3 A A A Ethyl CH3CHCH2CH3 CH3CHCH2CH2CHCH2CH3 76 CHAPTER 2 Structure and Reactivity A methyl-substituted butane An ethyl- and methyl-substituteddecane (A methylbutane) (An ethylmethyldecane) If a molecule has two or more chains of equal length, the chain with the largest number If a molecule has two or moreof substituentschains of is equalthe baselength, stem chain.the chain with the largest number of substituents is the base stem chain. CH3 CH3 CH3 CH3 A A A A CH3CHCHCHCHCH2CH3 not CH3CHCHCHCHCH2CH3 A A A A CH3 CH2 CH3 CH2 A A CH2 CH2 A A CH3 CH3 4 substituents 3 substituents A heptane A heptane Correct stem chain Incorrect stem chain 12 Here are two more examples, drawn with the use of bond-line notation:

Ethyl Methyl

A methylbutane An ethylmethyldecane

IUPAC Rule 2. Name all groups attached to the longest chain as alkyl substituents. For straight-chain substituents, Table 2-5 can be used to derive the alkyl name. However, what if the substituent chain is branched? In this case, the same IUPAC rules apply to such complex substituents: First, ! nd the longest chain in the substituent; next, name all its substituents.

IUPAC Rule 3. Number the carbons of the longest chain beginning with the end that is closest to a substituent.

CH3 7 3 4 2 1 8 5 CH3CHCH2 CH3 6 1 2 43 4not 3 21 not 4321 65 7 8 If there are two substituents at equal distance from the two ends of the chain, use the alphabet to decide how to number. The substituent to come ! rst in alphabetical order is attached to the carbon with the lower number.

CH CH CH 3 2 3 16 14 12 10 8 6 4 2

CH3CH2CHCH2CH2CHCH2 CH3 1 123 456 78 17 15 13 11 9 7 5 3 Ethyl before methyl Butyl before propyl What if there are three or more substituents? Then number the chain in the direction that gives the lower number at the ! rst difference between the two possible numbering schemes. This procedure follows the ! rst point of difference principle.

CH3 CH3 CH3 CH CH CHCH CH CH CH CHCH CHCH CH Numbers for 3 2 2 2 2 2 2 2 3 substituted carbons: 123 45678 9 10 11 12 3, 8, and 10 (incorrect) 1112 10 9 678 5 4 3 12 3, 5, and 10 (correct; 5 lower than 8) 3,5,10-Trimethyldodecane Substituent groups are numbered outward from the main chain, with C1 of the group being the carbon attached to the main stem. 76 CHAPTER 2 Structure and Reactivity 76 CHAPTER 2 Structure and Reactivity

If a molecule has two or more chains of equal length, the chain with the largest number of substituents is the base stem chain. If a molecule has two or more chains of equal length, the chain with the largest number of substituents is the base stem chain.CH3 CH3 CH3 CH3 A A A A CH3 CHCH3CHCHCH3 CHCH2CH3 notCH3 CHCH3CHCHCH3 CHCH2CH3 A A A A A A A A CH3CHCHCHCHCHCH3 2CHCH3 2 not CH3CHCHCHCHCHCH32CHCH3 2 A A A A A A CH3 CH2 CH2 CH3 CH2 CH2 A A A A CH2 CH CH2 CH A 3 A 3 4 substituents 3 substituents CH3 CH3 A heptane A heptane 4 substituentsCorrect stem chain 3 substituentsIncorrect stem chain A heptane A heptane Here Correctare two stem more cha inexamples, drawn with theIncorrect use of stem bond-line chain notation:

Here are two more examples, drawn with the use of bond-line notation: Ethyl Methyl Ethyl Methyl

A methylbutane An ethylmethyldecane A methylbutane An ethylmethyldecane IUPAC Rule 2. Name all groups attached to the longest chain as alkyl substituents. For IUPAC Rulestraight-chain 2. Name all substituents, groups attached Table to 2-5 the can longest be used chain to derive as alkyl the substituents.alkyl name. However, For what if IUPAC Rule 2.straight-chainName allthegroups substituents, substituentattached Tablechain 2-5isto branched? canthe belongest used In tothis derivechain case, the theas alkyl samealkyl name. IUPACsubstituents However, rules apply what. to if such complex First, find the longestthe substituentchainsubstituents: chainin the is branched?substituent First, ! nd In the this; longestnext, case, thenamechain same inall theIUPACits substituent;substituents rules apply next, to name. such allcomplex its substituents. substituents: First, ! nd the longest chain in the substituent; next, name all its substituents. IUPAC Rule 3. Number the carbons of the longest chain beginning with the end that is IUPAC Rule 3IUPAC. Number Rule closest the 3. Number carbonsto a substituent. the carbonsof the oflongest the longestchain chainbeginning beginning withwith thethe endend that isthat is closest to a substituent closest to a. substituent.

CH3 7 3 4 2 1 CH3 8 5 CH CHCH CH 7 3 6 3 2 3 4 2 1 8 5 CH3CHCH2 CH1 3 2 43 6 1 2 43 4not 3 21 not 4321 65 7 8 If there4not are3 two21 substituentsnot at equal distance4321 from65 7 the8 two ends of the chain, use the If there are two substituentsIf there arealphabet two atsubstituents to equal decide distancehowat equal to number. distancefrom The fromthe substituent twothe twoends ends to come ofof thethe ! rstchain,chain, in alphabeticaluse usethe the order is alphabet to decidealphabethow to attached decideto number how to the to. number.carbonThe substituentwith The the substituent lowerto number. tocome come first! rst inin alphabeticalalphabetical orderorder is is attached to theattachedcarbon towith the carbonthe lower with thenumber lower .number.

CH CH CH 3 2 3 16 14 12 10 8 6 4 2 CH CH CH 3 2 3 16 14 12 10 8 6 4 2 CH3CH2CHCH2CH2CHCH2 CH3 1 123 456 78 17 15 13 11 9 7 5 3 CH3CH2CHCH2CH2CHCH2 CH3 1 123 45Ethyl6 78before methyl 17 15 13 11 9 Butyl7 before5 propyl3 Ethyl before methylWhat if there are three or more substituents?Butyl before Thenpropyl number the chain in the direction13 What if that there gives are three the lower or more number substituents? at the ! Thenrst difference number thebetween chain the in thetwo direction possible numbering that gives theschemes. lower numberThis procedure at the ! followsrst difference the ! rst between point ofthe difference two possible principle. numbering schemes. This procedure follows the ! rst point of difference principle. CH3 CH3 CH3 CH3 CH3 CH3 CH CH CHCH CH CH CH CHCH CHCH CH Numbers for 3 2 2 2 2 2 2 2 3 substituted carbons: CH CH CHCH CH CH CH CHCH CHCH CH Numbers for 3 2 122 2 3 245672 2 8 2 9 3 10 substituted11 12 carbons:3, 8, and 10 (incorrect) 123 45671112 10 9 8 9 10678 115 124 3 3, 8, and12 10 (incorrect)3, 5, and 10 (correct; 1112 10 9 678 5 4 3 12 3, 5, and 10 (correct;5 lower than 8) 3,5,10-Trimethyldodecane 5 lower than 8) Substituent groups3,5,10-Trimethyldodecane are numbered outward from the main chain, with C1 of the group being Substituent groupsthe carbon are numberedattached tooutward the main from stem. the main chain, with C1 of the group being the carbon attached to the main stem. IUPAC Rule 4. Write the name of the alkane by first arranging all the substituents in 2-6 Naming the Alkanes CHAPTER 2 77 alphabetical order (each preceded by the carbon number to which it is attached and a hyphen) and then adding the name of the stem. Should a molecule containIUPAC moreRule 4.than Writeone the nameof a particularof the alkanesubstituent, by ! rst arrangingits name all the issubstituentspreceded in by alphabetical order (each preceded by the carbon number to which it is attached and a 3 the prefix di, tri, tetra, penta, and so forth. 1 hyphen) and then adding the name of the stem. Should a molecule contain more than 5 2 4 The positions of attachmentone of a particularto the stemsubstituent,are itsgiven name collectivelyis preceded by beforethe pre! xthe di, tri,substituent tetra, penta, nameand so forth. The positions of attachment to the stem are given collectively before the sub- 5-Ethyl-2,2-dimethyloctane and are separated bystituentcommas name. and are separated by commas. These pre! xes, as well as sec- and tert-, (‘‘di’’ not counted in are not considered in the alphabetical ordering, except when they are part of a complex alphabetical ordering) These prefixes, as wellsubstituentas sec name.- and tert-, are not considered in the alphabetical ordering, but except when they are part of a complex substituent name.

CH3 CH3 CH3 CH3 1 CH3CHCH2 CH3 CH3CHCHCH3 CH3CHCH2CH2 CHCH2CCH3 35 4 2 CH3 CH3CH2 CH3 5-(1,1-Dimethylethyl)-3- 2-Methylbutane 2,3-Dimethylbutane 4-Ethyl-2,2,7-trimethyloctane ethyloctane (‘‘di’’ counted: part of substituent name) CH2CH3

CH3CH2CHCHCH3

CH3 14 4,5-Diethyl-3,6-dimethyldecane 3-Ethyl-2-methylpentane

The ! ve common group names in Table 2-6 are permitted by IUPAC: isopropyl, i s o b u t y l , sec-butyl, tert-butyl, and neopentyl. These ! ve are used universally in the course of normal communication between scientists, and it is necessary to know the structures to which they refer. Nonetheless, it is preferable to use systematic names, especially when searching for information about a chemical compound. The online databases containing such information are constructed to recognize the systematic names; therefore, use of a common name as input may not result in retrieval of a complete set of the information being sought. The systematic name of a complex substituent should be enclosed in parentheses to avoid possible ambiguities. If a particular complex substituent is present more than once, a special set of pre! xes is placed in front of the parenthesis: bis, tris, tetrakis, pentakis, and so on, for 2, 3, 4, 5, etc. In the chain of a complex substituent, the carbon numbered one (C1) is always the carbon atom directly attached to the stem chain.

First substituent at position 2 CH3 Complex alkyl group determines numbering has carbon 1 attached to 2 CH2 the base stem 3 1 Longest chain CH2 2 64 8 chosen has CH3 1 highest number 3 9 CH CH 5 7 of substituents CH3CH 2 3 CH C CH CH3CH2CH2CHCH2CH2 CH3 3 4-(1-Ethylpropyl)-2,3,5-trimethylnonane 4-(1-Methylethyl)heptane (4-Isopropylheptane) CH2 H

CH2 CH3

Exercise 2-19 CH C CH3

Write down the names of the preceding eight branched alkanes, close the book, and reconstruct CH2 H their structures from those names. CH2

CH2 To name haloalkanes, we treat the halogen as a substituent to the alkane framework. As usual, the longest (stem) chain is numbered so that the ! rst substituent from either end CH3 receives the lowest number. Substituents are ordered alphabetically, and complex append- 5,8-Bis(1-methylethyl)- dodecane ages are named according to the rules used for complex alkyl groups. To name haloalkanes, we treat the halogen as a substituent to the alkane framework. As usual, the longest (stem) chain is numbered so that the first substituent from either end receives the lowest number. 78 CHAPTER 2 Structure and Reactivity Substituents are ordered alphabetically, and complex appendages are named according to the rules used for complex alkyl groups.

CH3 CH3 A A CH3COBr FCH2CCH3 Cl A A CH3I CH3 H Iodomethane 2-Bromo-2-methylpropane 1-Fluoro-2-methylpropane 6-(2-Chloro-2,3,3-trimethylbutyl)undecane

Common names are based on the older term alkyl halide. For example, the ! rst three Common names are basedstructureson abovethe haveolder the commonterm alkyl nameshalide methyl . iodide,For tertexample,-butyl bromide,the andfirst isobutylthree structures above have the" uoride,common respectively.names Some chlorinatedmethyl iodide, solvents havetert -commonbutyl bromide, names: for example,and isobutyl carbon tetrachloride, CCl ; chloroform, CHCl ; and methylene chloride, CH Cl . fluoride, respectively. 4 3 2 2

Some chlorinated solventsExercisehave 2-20common names: for example, carbon tetrachloride, CCl4; chloroform, CHCl3; and methyleneDraw the structurechloride, of 5-butyl-3-chloro-2,2,3-trimethyldecane.CH2Cl2.

15 Further instructions on nomenclature will be presented when new classes of compounds, such as the cycloalkanes, are introduced. In Summary Four rules should be applied in sequence when naming a branched alkane: (1) Find Really the longest chain; (2) ! nd the names of all the alkyl groups attached to the stem; (3) number the chain; (4) name the alkane, with substituent names in alphabetical order and preceded by numbers to indicate their locations. Haloalkanes are named in accord with the rules that apply to naming the alkanes, the halo substituent being treated the same as alkyl groups.

2-7 STRUCTURAL AND PHYSICAL PROPERTIES OF ALKANES

The common structural feature of all alkanes is the carbon chain. This chain in" uences the physical properties of not only alkanes but also any organic molecules possessing such a backbone. This section will address the properties and physical appearance of such structures. Alkanes exhibit regular molecular structures and properties The structural features of the alkanes are remarkably regular. The carbon atoms are tetrahedral, with bond angles close to 1098 and with regular C – H (< 1.10 Å) and C – C (< 1.54 Å) bond lengths. Alkane chains often adopt the zigzag patterns used in bond-line notation (Figure 2-3). To depict three-dimensional structures, we shall make use of the hashed-wedged line notation (see Figure 1-23). The main chain and a hydrogen at each end are drawn in the plane of the page (Figure 2-4).

Exercise 2-21 Draw zigzag hashed-wedged line structures for 2-methylbutane and 2,3-dimethylbutane.

Figure 2-3 Ball-and-stick (top) and space-! lling molecular models of hexane, showing the zigzag pattern The longest man-made linear of the carbon chain typical of the alkanes. [Model sets courtesy of alkane is C390H782, synthesized as a molecular model for Maruzen Co., Ltd., Tokyo.] polyethene (polyethylene). It crystallizes as an extended chain, but starts folding readily (picture) at its melting point of 1328C, in part due to attractive intramolecular London forces.