Organic Chemistry Pharmacy
REPRESENTATION OF MOLECULES
Lewis’ formulas
All valence electrons (either involved in bond or unshared pairs) are represented with dots .. H + H : : H ...... C..l .. H.. .. H:O:H H:N:H : H:C::C:H H:C:::C:H .. H:N..:H .. H:C..:H :C..l:C..:C..l H H : : . H C..l Kekulé’s formulas Also called valence-bond formulas
Each electron pair shared in covalent bonds is indicated with a dash (unshared pairs can be omitted or represented with dots) + .. .. H or H-O-H H-O-H .. H-N-H or H-N-H H N H H H H
.. :Cl: H H Cl H .. .. H C H C C H C C H Cl-C-Cl or : C..l-C-C..l : H H H Cl : Cl.. : Organic Chemistry Pharmacy
H H H H C H H H C H H H H :O: H H Long and painstaking H C C C C C C C C C H representation with H H C H H H H H HH C H H complex molecules H H Condensed Structural Formulas
Molecule is written as a sequence of C atoms. Each C is followed by the atoms bound to it; the brackets are used in ambiguous cases. The first C on the left can be preceded by the atoms linked to it.
H H or H CCH H C C H CH3CH3 3 3 H H H F H F is monovalent, therefore it does not H C C C H CH3CHFCH3 generate ambiguity H H H H H H O is bivalent and it is clear that the H H C C C O H CH CH CH OH 3 2 2 on its right is bound to it H H H Organic Chemistry Pharmacy
H H H Bracket helps to avoid H C C C H CH3CH(OH)CH3 missunderstanding H OH H Equal groups linked to the same C are written only once, collected in brackets, with an index that tells how many equal groups are related to that C H H H H C H H H C H H H H : O: H H H C C C C C C C C C H (CH3)3CCH2CH2CH(CH3)CH2CH(OH)CH(CH3)2 H H C H H H H H HH C H H H H multiple bonds (double and triple) MUST always be written H H or H C=CH H C C H CH2=CH2 2 2 H C C H HC CH
CAUTION!!!! Notice the difference between the following condensed formulas
H H H H .. CH C(O)CH CH OCH = H C O C H = H C C C H 3 3 3 3 .. CH3COCH3 H H H :O: H Organic Chemistry Pharmacy
Semi-condensed Formulas
When condensed formulas are not sufficiently clear, "semicondensed" formulas can be used. Bonds among C atoms are evidenced with a dash.
Examples
(CH3)3CCH2CH2CH(CH3)CH2CH(OH)CH(CH3)2 condensed formula
CH3 OH
CH3 C CH2 CH2 CH CH2 CH CH CH3 semi-condensd formula CH CH CH3 3 3 Multiple bonds (double and triple) must ALWAYS be written
Bond-line formulas
This representation is very simple, but rules must be well understood, in order to write and read the molecules correctly ● C-C bonds are indicated with a line ● The H atoms linked to C atoms are omitted (this means that those bound to atoms other than C must be written). ● C bonds with atoms other than H are indicated (with lines). Organic Chemistry Pharmacy
H F H F F H C C C H CH3CHFCH3 CH3 CH CH3 H H H
H H H H C C C O H OH CH3CH2CH2OH CH3-CH2-CH2-OH H H H
H H H H H H H
H C C C C C C C H CH3CH2CH2CH2CH2CH2CH3 H H H H H H H CH3-CH2-CH2-CH2-CH2-CH2-CH3 Organic Chemistry Pharmacy
H H H OH OH
H C C C H CH3CH(OH)CH3 CH3 CH CH3 H OH H H H C H H H H H H H
H C C C C C C C H CH3CH2CH2CH(CH3)CH2CH2CH3
H H H H H H H CH3
CH3 CH2 CH2 CH CH2 CH2 CH3 Organic Chemistry Pharmacy H H C H H H H H H H CH3CH2CH2C(CH3)2CH2CH2CH3
H C C C C C C C H CH3
H H H H H H CH3 CH2 CH2 C CH2 CH2 CH3 H C H CH3 H
H H C H H H H CH3 (CH ) CCH CH H C C C C H 3 3 2 3 CH3 C CH2 CH3
CH3 HH C HH H H
(CH3)3CCH2CH2CH(CH3)CH2CH(OH)CH(CH3)2 OH Organic Chemistry Pharmacy
CH (CH ) CH 3 2 5 3 CH3-CH2-CH2-CH2-CH2-CH2-CH3 condensed formula semi-condensed formula bond-line formula
CH3 CH CH3CH2C(CH3)2CH(CH3)CH2CH3 CH3 CH2 C CH CH2 3 CH3 CH3 condensed formula semi-condensed formula
bond-line formula
Bond-line formulas are particularly useful when rings must be represented.
H H H H C CH C C 2 H H H2C CH2 CH H C C H H2C 2 CH H C H 2 Bond-line Formula H H Semi-condensed Formula Kekulé’s Formula CAUTION! Condensed formulas CANNOT BE USED to write rings. (CH2)6 Organic Chemistry Pharmacy
Examples
H H H H
H C C C C H CH3CHClCH2CH3 H Cl H H
H C CH CH CH 3 2 3 Cl Cl
H H H H H C C C C H H H H CH CH(CH )CH CH H C H 3 3 2 3 H
H3C CH CH2 CH3
CH3 Organic Chemistry Pharmacy
H H CH CH OH H C C O H CH3CH2OH 3 2 H H OH H H H H H H H C C H OH H H O H
H H H ...... H H H H H H .. H : C : C : C : O : H ...... H C C C O H or H C C C O.. H H H H H H H H H H Kekulé
CH CH CH OH CH3CH2CH2OH 3 2 2
OH Organic Chemistry Pharmacy
TRIDIMENSIONAL REPRESENTATION To represent a molecule showing the three-dimensional situation of atoms, the following rules apply:
• The bonds that join atoms belonging to the same plane (writing plane) are indicated with a line
• Bonds that come out of the writing plane, toward the viewer, are indicated with solid wedges. The atom at the wide end of the solid edge is in ftont of the writing plane. • Bonds that pointing back the writing plane are represented with a broken wedge
For a given molecule, which atoms belong to the writing plane depends on how the molecule is oriented in space (remembering that a plan passes through three points). H H H C C H H C H H H H H H H Organic Chemistry Pharmacy
CONVENTIONS FOR WRITING REACTIONS
A B An arrow indicates an irreversible transformation. The tip of the arrow is directed towards the product of the reaction.
A B An equilibrium reaction is indicated by a double arrow.
If the balance is strongly displaced in one A B direction, the corresponding arrow is longer than the other Electron movements are represented by curved arrows, with the tip in the direction of electron movement. An arrow with a normal tip is used to move an electron pair
+ - - + A: + B A-B A + :B A-B
To indicate the movement of a single electron, an half-tip arrow is used
A. + . B A-B Organic Chemistry Pharmacy
The molecular formula is not sufficient to completely characterize a compound
it is a simple formula but with this molecular formula there C2H6O are two compounds, with different physical and chemical properties
C H O H H 2 6 H H H C C O H H C O C H H H H H ethanol dimethyl ether
Ethanol and dimethyl ether are structural isomers Organic Chemistry Pharmacy
Structural isomers: compounds that have the same molecular formula, but different arrangement of atoms
The problem grows rapidly as the number of C atoms increases
with 9 atoms of C and only H as other 35 structural isomers element (C9H20)
with 30 C atoms (C H ) 30 62 4 111 846 763 structural isomers
It is necessary a system of identification of organic compounds that allows, given a name, to write the corresponding formula and vice versa, univocally IUPAC Nomenclature Organic Chemistry Pharmacy
ORGANIC COMPOUNDS CLASSIFICATION
ORGANIC COMPOUNDS
ALIPHATICS CYCLICS
HOMOCYCLICS HETEROCYCLICS
ALICYCLICS AROMATICS
Compounds made up with C and H only are called HYDROCARBONS Organic Chemistry Pharmacy
3 ALKANES Hydrocarbons in which all C atoms have sp hybridizatation
general formula CnH2n+2
The foundations of the IUPAC system are the names of the continuous-chain alkanes RULE Alkane’s name is made by adding the ending -ane to a root, which indicates how many are the carbon atoms in the molecule.
For alkanes with numbers of C atoms from 1 to 4, “traditional trivial" roots are used. For alkanes with higher numbers of C atoms, the names come from Latin or Greek numbers. H H H H C CH4 methane C C H H H 2 6 H C H H H ethane H H H H H C H H H C H C 3 8 H C C H C C 4 10 C C H propane H butane H H H H H H H Organic Chemistry Pharmacy
H H H H C H C H C H C C C 5 12 pentane H H H H H H
root "met-" 1 C root “prop-" 3 C root "eth-" 2 C root “but-" 4 C
number Name Condensed Formula Bond-line Formula of C METHANE 1 CH4 2 ETHANE CH3CH3 3 PROPANE CH3CH2CH3 4 BUTANE CH3(CH2)2CH3
5 PENTANE CH3(CH2)3CH3 Organic Chemistry Pharmacy
Names of the higher members of this series consist of a numerical term, followed by "-ane" with elision of terminal "a" from the numerical term.
C numb. Name Condensed Formula Bond-line formula
HEXANE 6 CH3(CH2)4CH3
7 HEPTANE CH3(CH2)5CH3
8 OCTANE CH3(CH2)6CH3
9 NONANE CH3(CH2)7CH3 DECANE 10 CH3(CH2)8CH3
For alkanes with the number of C atoms between 11 and 19, the root is made by "deca-“ preceded by the indication of the units. C H 11 24 UNDECANE CH3(CH2)9CH3 Organic Chemistry Pharmacy
n. C empirical formula name Condensed Formula Bond-line formula
11 C11H24 UNDECANE CH3(CH2)9CH3
12 C12H26 DODECANE CH3(CH2)10CH3
13 CH (CH ) CH C13H28 TRIDECANE 3 2 11 3
14 C14H30 TETRADECANE CH3(CH2)12CH3
15 C15H32 PENTADECANE CH3(CH2)13CH3
16 C H 16 34 ESADECANE CH3(CH2)14CH3
17 C H 17 36 EPTADECANE CH3(CH2)15CH3
18 C18H38 OTTADECANE CH3(CH2)16CH3
19 C19H40 NONADECANE CH3(CH2)17CH3 Organic Chemistry Pharmacy
Alkane with 20 C atoms (C20H42) is called eicosane o icosane. »Cosa-» as root is used indicate the numeber 20, for compound with a number of C raging from 21 to 29
n. C empirical formula name Condensed Formula
21 C21H44 UNICOSANE CH3(CH2)19CH3 CH (CH ) CH 22 C22H46 DOCOSANE 3 2 20 3
23 CH3(CH2)21CH3 C23H48 TRICOSANE CH3(CH2)22CH3 24 C24H50 TETRACOSANE CH (CH ) CH 25 C25H52 PENTACOSANE 3 2 23 3
26 C26H54 ESACOSANE CH3(CH2)24CH3
27 C27H56 EPTACOSANE CH3(CH2)25CH3 28 C28H58 OTTACOSANE CH3(CH2)26CH3 29 C H 29 60 NONACOSANE CH3(CH2)27CH3 Organic Chemistry Pharmacy
When C atoms are more than twenty, root "conta-» is used, preceded by a prefix indicating how may sets of ten are present.
n. C empirical formula name Condensed Formula
30 C H 30 62 TRIACONTANE CH3(CH2)28CH3 40 C H 40 82 TETRACONTANE CH3(CH2)38CH3 50 C50H102 PENTACONTANE CH3(CH2)48CH3
60 C60H122 ESACONTANE CH3(CH2)58CH3
70 C70H142 EPTACONTANE CH3(CH2)68CH3 80 C H 80 162 OTTACONTANE CH3(CH2)78CH3
90 C90H182 NONACONTANE CH3(CH2)88CH3
100 C100H202 HECTANE CH3(CH2)98CH3
Units precede the set of ten: C43H88 TRITETRACONTANE Organic Chemistry Pharmacy
In order to write down compuonds formula from name, it is advisable to separate it in its costituents, starting from the right end and moving to left
dotetracontahectane DO - TETRA - CONTA - HECT - ANE 1 2 3 4 C sp3, H C142 H 286 5 hunders tens four two With these simple rules names and formulas of all continuous-chain alkanes can be written.
But .... not all alkanes have all C atoms linked in one chain!
Whereas there is an only way to connect two or three C atoms together, there are different ways to link 4 atoms of C: C C C C butane? with 4 C C4H10 C C C C Two different molecules CANNOT have the same name! Organic Chemistry Pharmacy
The two “butanes” differ only in disposition of C atoms C C C C C C C C
linear sequence branched sequence
The name butane is given to the linear compound, while the branched structural isomer add to butane the prefix "iso-".
CH3 CH2 CH2 CH3 butane
CH CH3 CH 3 isobutane CH3 As the C number increases, the number of structural isomers increases as well C with 5 C C C C C C C C C C C C C ? C C pentane Prefix iso- is not enough!! There must be a different solution..... Organic Chemistry Pharmacy
The "iso-" prefix may be used to name an alkane with only one branch, made of a single C, linked immediately after one of the two ends. CH CH CH3 CH CH2 CH2 2 3 C7H16 isoheptane
CH3 C H isooctane CH3 CH2 CH2 CH2 CH2 CH CH3 8 18
CH3 but CH CH CH3 CH2 CH CH2 2 3 ?
CH3
Before addressing the problem, let’s give some definition
a C bound to only one C atom is called primary carbon a C bound to two C atoms is called secondary carbon
a C bound to three C atoms is called tertiary carbon a C bound to four C atoms is called quaternary carbon Organic Chemistry Pharmacy
C primary C C C C C C C C C C C C C C C C secondary C secondary C quaternary C tertiary
Although H atoms can all be linked to one C only, they are indicated accordingly: H is called "primary" when it is linked to a primary C, "secondary" when it is linked to a secondary C, and "tertiary" when it is bound to a tertiary C
If an atom of hydrogen is removed from a terminal C atom of a linear alkane, a free valence remains on this C and the resulting group is called alkyl. RULE The alkyl group from an alkane is named by replacing with the ending “yl” the desinence "-ane " in the name of the parent hydrocarbon. Organic Chemistry Pharmacy
CH METHANE CH H 4 3 CH3 METHYL
CH CH ETHANE CH CH H ETHYL 3 3 3 2 CH3 CH2
They are the = SAME group
In methane and in ethane all H are equivalent and therefore the resulting alkyl is unique. With propane the same akyl group is obtained removing one of the six equivalent primary H.
= Organic Chemistry Pharmacy
Hoever, a different alkyl group is obtained removing either of the two secondary equivalent H atoms.
The alkyl group from propane with the free valence on primary carbon is named propyl. The alkyl group from propane with the free valence on secondary carbon is named adding the prefix “iso”: isopropyl.
CH3 CH2CH2 H CH3 CH2 CH2 PROPYL
CH3CH2CH3 CH CH CH CH CH CH ISOPROPYL PROPANE 3 3 3 3 H
The number of isomeric alkyls is larger than the number of isomeric alkanes! Then, WHY alkyls were introduced? ...... Organic Chemistry Pharmacy
Both isomeric alkanes of formula C4H10 have two types of H (primary and secondary) and therefore give two different alkyls each.
CH3-CH2-CH2-CH3 =
6 equivalent primary H 4 equivalent secondary H =
CH3-CH-CH3 - CH3
= =
9 equivalent primary H 1 tertiary H Organic Chemistry Pharmacy
When the free valence is on the primary C, the name of the alkyl is formed by replacing the ending "-ane“ of the parent hydrocarbon by the ending"-yl”.
CH3 CH2 CH2 CH3 CH3 CH2 CH2 CH2 butyl butane
CH CH CH CH3 CH CH3 3 2 isobutyl CH CH3 3 isobutane The other alkyls are distinguished with a prefix that indicates the type of C with the free valence is an alkyl with free valence (secondary from butane, prefix “sec-” and tertiary from isobutane, prefix “tert-”, respectively). CH CH CH CH 3 2 2 3 CH3 CH2 CH CH3 sec-butyl butane
CH3 CH CH3 CH C 3 CH3 tert-butyl CH3 CH3 isobutane Organic Chemistry Pharmacy
Alkyl groups are used to name to the branched alkanes
RULES TO NAME A BRANCHED ALKANE 1. The longest continuous chain of carbon atoms is identified and is considered the parent name. 2. The side chains are called with the name of the corresponding alkyl group and precede the parent name. 3. The position that the side chains occupies in the main chain is indicated by a number, which precedes the name of the alkyl group, separated by a dash. 4. The longest chain is numbered frorn one end to the other by Arabic numerals, the direction being so chosen as to give the lowest numbers possible to the side chains. Organic Chemistry Pharmacy
Example: CH3 CH2 CH CH2 CH3
CH3 Longest chain: 5 C parent name: pentane side chain: 1 C sobstituent name: methyl position: 3 (same distance from both ends)
complete name 3-methylpentane 1 2 3 4 5 5 4 3 2 1 CH CH CH CH CH 3 2 2 3 = CH3 CH2 CH2 CH CH3
CH3 CH3 Longest chain : 5 C parent name : pentane side chain: 1 C sobstituent name : methyl position: 2 (numbered from the end closest to the branching)
complete name 2-methylpentane Organic Chemistry Pharmacy
1 2 2 1 5 4 4 5 C C C C C C C C C C C C 3 C 3 C 3 C 3 C 4 C 4 C 2 C 2 C 5 C 5 C 1 C 1 C correct correct wrong wrong numbering numbering numbering numbering
2 2
2 2
2 2
2 2 Organic Chemistry Pharmacy
If the branching position is unique, the number is superfluous and it is omitted 1 1 In a 4 carbons continuous chain CH CH CH CH CH CH CH CH 3 2 3 3 2 3 ramification can occur ONLY at the CH 3 CH3 position close to one end Longest chain : 4 C parent name : butane side chain: 1 C sobstituent name : methyl position: 2 (and only 2: unnecessary)
complete name methylbutane
5. When there are more ramifications, the numbering of the longest continuous chain must start from the end that allows to give the lowest number at the first difference.
1 2 3 4 5 6 Wrong numbering 6 5 4 3 2 1 Right numbering CH CH CH CH3 CH CH2 3 (First branching has the same number as above, but CH the second branch has a lower number) CH3 CH3 3 This principle is applied irrespective of the nature of the substituents. Organic Chemistry Pharmacy
6. If there are more equal alkyl groups, the alkyl group is nominated only once, preceded by a multiplicative prefix (that indicates how many equal alkyl groups there are) and by as many numbers as there are groups, separated by a comma.
6 5 4 3 2 1 1 2 3 4 5 6
CH3 CH2 CH CH CH2 CH3
CH3 CH3 Longest chain : 6 C parent name : hexane side chain : 1 C substituent name : methyl number of sobstituents: two moltiplicative prefix di positions: 3,4
complete name: 3,4-dimethylhexane Organic Chemistry Pharmacy
CH 6 5 4 3 3 Longest chain : C6 CH CH CH C CH2 CH parent name : hexane 3 2 2 2 1 3 CH side chain : C1 3 sobstituent name : methyl number of sobstituents : 2 moltiplicative prefix di position : 3 e 3
3,3-dimethylhexane
MULTIPLICATIVE PREFIXES number number number of equal prefix of equal prefix of equal prefix groups groups groups 2 di- 5 penta- 8 octa- 3 tri- 6 hexa- 9 nona- 4 tetra- 7 hepta- 10 deca- Organic Chemistry Pharmacy
7. If there are different alkyl groups, they must be alphabetically listed, separated by a dash, each preceded by the number of the C they are linked to. With the same numbering, the lowest number belongs to the first group in alphabetical order.
7 6 5 4 3 2 1 7 6 5 4 3 2 1 CH3 CH2 CH2 CH CH CH2 CH3 CH3 CH2 CH2 CH CH CH CH CH3 CH2 2 3 CH2 CH3 CH3 CH 3-ethyl-4-methylheptane 3 4-ethyl-3-methylheptane 6 5 4 3 2 1
CH3 CH2 CH CH CH2 CH3 CH CH CH 3 2 3 9 8 7 6 5 4 3 2 1 CH CH CH CH CH CH CH CH CH 3-ethyl-4-methylhexane 3 2 2 2 2 2 3 CH 3 CH2 CH2 CH3
5-methyl-4-propylnonane Organic Chemistry Pharmacy
CH 5 3 CH3 CH2 CH2 CH CH CH2 CH2 CH3 4 3 2 1 6 CH2
CH2 CH2 CH3 7 8 9
4-methyl-5-prophylnonane Prefixes iso-, sec-, terz- and all those who are an integral part of the name must be considered when establishing the alphabetical order.
Multiplicative prefixes, which indicate how many groups of a type are present, are not part of the name and therefore are not considered when establishing the alphabetical order.
7 6 5 4 3 CH3 1 2 3 4 CH3 2 1 5 CH CH CH3 CH2 CH2 CH C 2 3 CH3 CH2 CH CH CH CH2 CH3 6 7 CH CH CH CH 2 3 CH3 3 CH 3 CH3 4-ethyl-3,3-dimethylheptane 4-isopropyl-3,5-dimethylheptane Organic Chemistry Pharmacy
The names of the non-primary alkyl groups with 3 and 4 C atoms (isopropyl, isobutyl, sec-butyl, tert-butyl) are accepted by the IUPAC. For alkyl groups with a C> 4 number one must resort to a systematic nomenclature.
RULE The branched alkyl groups are called identifying the longest chain starting from the free valence and giving the ending "-yl" at the corresponding parent name. The ramifications precede the name of the alkyl. At C with the free valence (ie the one linked to the main chain) is assigned the number 1; if necessary, parentheses are used to avoid ambiguity.
1 2 3 4 5 6 7 8 9 10 11 12 CH CH CH CH CH CH3 CH2 CH2 CH2 CH2 CH CH2 2 2 2 2 3
1 CH CH3
CH2 CH2 CH3 2 3 4 Longest chain : 12 C (parent name dodecane) Position of the substituent in the chain : 6 longer chain of the substituent : 4 C (alkyl name butyl) substituent of the substituent: 1 C Position in the main substituent : 1 substituent name: 1-methylbutyl first letter for the alphabetical order : m 6-(1-methylbutyl)dodecane Organic Chemistry Pharmacy
If in a molecule the longest chains (with the same number of atoms of C) are more than one, the choice of the main chain is made using, in order, the following criteria (listed from the most to the least important):
1. The chain with the largest number of side chains is chosen
3 7 6 5 4 3 2 1 1 2 3 4 4 2 1 CH CH CH CH CH CH CH CH3 CH2 CH CH CH CH CH3 CH3 CH2 CH CH CH CH CH3 3 2 3 5 5 CH CH CH CH CH CH CH CH3 CH2 3 3 CH3 CH2 3 CH3 3 2 3 3 CH CH CH CH CH2CH3 2 3 2 3 6 7 6 7 neither 2,3-dimethyl-4-sec-butylheptane nor 2,3,5-trimethyl-4-propylheptane 4-(1,2-dimethylpropyl)-3-methylheptane 2. The chain with the lower numbers for the side chains is chosen CH 1 2 3 4 5 3 1 2 3 4 CH3 CH3 CH CH2 CH CH2 CH CH3 CH3 CH CH2 CH CH2 CH CH3 CH 6 7 3 CH CH CH3 3 5 C CH3 CH2 6 CH2 7 CH CH3 3 4-isobutyl-2,5-dimethyl-heptane not 2,6-dimethyl-4-sec-butylheptane Organic Chemistry Pharmacy
CYCLOALKANES 3 Hydrocarbons with all Cs hybridized sp , general formula CnH2n RULE The names of saturated monocyclic hydrocarbons, with all C sp3, are formed by attaching the prefix "cyclo-" to the name of the acyclic alkane with the same number of carbon atoms.
CH H2C CH2 2 H2C CH2 CH CH H2C CH2 2 2 H C CH 2 2 CH2 Cyclopropane cyclobutane cyclopentane
H CH CH 2 2 2 CH2 C H C CH 2 2 CH2 CH2 H2C CH2 H C CH CH H C CH 2 2 2 CH2 2 C 2 CH CH cyclohexane 2 2 CH2 cyclotetradecane H2 In a cycloalkane all positions are equivalent and numbering can start from any of the atoms.
1 4 1 2 1 1 1 3 4 3 2 Organic Chemistry Pharmacy
If there is a substituent, this automatically identifies the position 1 of the ring. In giving the name, the position of the substituent is omitted (because it can not be other than 1.
CH2CH3 1 1 1 1 H C 3 CH3 CH3 methylcyclobutane ethylcyclopentane methylcycloheptane methylcycloundecane If substituents are more than one, numbering must be given so that the substituents have the lowest possible numbers. Each substituent will be preceded by the number indicating its position in the ring. H3C 2 H C 3 1 2 1-ethyl-3-methylcyclopentane 1 3 2 3 2 1 H C 3 CH CH 3 1 2 3 CH3 CH3 1,2-dimethylcyclopentane 1,3-dimethylcyclopentane CH3
CH3 1 CH 1 CH3 2 3 3 2 CH 3 3 CH CH 1 3-ethyl-1,1- 3 2 CH2 1,1-dimethylcyclopentane CH dimethylcyclohexane 1-ethyl-3-methylcyclohexane 3 Organic Chemistry Pharmacy
When the ring is the substituent, it is called "cycloalkyl" and it is listed together with the other substituents, in alphabetical order, preceded by the number which indicates its position in the main chain H2C CH2 H C CH = 2 cyclohexyl H2C CH2 “cycle-” as prefix is an integral part of the name and therefore must be considered when establishing the alphabetical order.
CH3 CH3 CH CH2 CH2 CH2 CH3 CH3 CH CH CH CH2 CH3 CH3 CH2CH3 methylcyclopentane 2-cyclopentylhexane 3-cyclohexyl-4-ethyl-2-methylhexane If two cycles are linked together by one C-C bond, one of them should be considered as the parent compound (with the ending "-ane"), while the other must be considered as a substitute (with the ending "-yl").
cyclohexylciclohexane cyclopentylcyclohexane Organic Chemistry Pharmacy
GUIDELINES TO WRITE THE NAME OF A COMPOUNDS FRPM THE FORMULA
1. In compounds’ name, there must be only one ending; 2. Identify the parent structure (longest chain or ring); 3. Name the parent structure; 4. Find out and list substituents, with respective prefix, in alphabetic order and with the numbers of the position they occupy in the parent structure. 5. Eventually, add moltiplicative prefix; 6. Link together substituent and parent structure name obtaining the complete name.
TIP: write the numbers on the atoms of the parent chain, so that you do not have to re-count them all the time! Organic Chemistry Pharmacy
GUIDELINES TO WRITE THE FORMULA FROM THE NAME example 3-ethyl-2,2-dimethylhexane
1. Consider the ending 3-ethyl-2,2-dimethylhexane
ane It means that it is an alkane (only atoms C and H, all C sp3)
2. Consider the root 3-ethyl-2,2-dimethylhexane
hex It means that the longest chain has 6 C atoms
3. Write down the 6-C chain leaving the space for H
C - C - C - C - C - C
4. Write down numbers, starting from one of the two ends (whichever)
1 2 3 4 5 6 6 5 4 3 2 1 C - C - C - C - C - C or C - C - C - C - C - C Organic Chemistry Pharmacy
5. Insert substituents as the number position suggests
3-ethyl-2,2-dimethylhexane It means that there are two methyl groups, both of them linked in position 2 and a etyhl group in position 3 CH CH3 4 6 6 5 4 3 3 1 2 3 5 2 1 C C C C C C or C C C C C C
CH2 CH3 CH3 CH2-CH3 CH3 6. Complete the formula adding H in order to have all the C atoms with the correct valence 4
CH3 FOLLOW THESE STEPS AND IT CH3 C CH CH2 CH2 CH3 MISTAKES WILL BE AVOIDED CH -CH CH3 2 3
7. If required, re-write the formula according to the rules of bond-lines formulas. Organic Chemistry Pharmacy
example 1-ethyl-2,2-dimethylcyclohexane
1. Consider the ending 1-ethyl-2,2-dimethylcyclohexane
ane It means that it is an alkane (only atoms C and H, all C sp3)
2. Consider the root 1-ethyl-2,2-dimethylcyclohexane cyclohex It means that the parent compound is a 6 C ring
C 3. Draw the ring C C or C C C
4. Write the first substituent in any position that becomes position 1
CH2CH3
C C CH2CH3 C C C CH3CH2 C C 1 C C 1 C C C C C C C C1 C C C C C C 1 C C 1 C C 1 C C C C C C CH2CH3 C CH3CH2 C C
CH2CH3 Organic Chemistry Pharmacy
5. Add the other substituents in the correct position that can be reached either in clockwise or counterclockwise way.
C CH C C C 3 C C CH C 2 C1 or 2 3 1 C CH2CH3 C C CH C CH2CH3 H3C 3
6. Complete the formula adding, for each C the rigth number of H to reach valence 4.
H2 H2 CH3 C C H C CH H C 2 C CH or 2 2 2 3 2 1 1 H2C CH H2C CH C CH CH C CH CH 2 3 2 3 CH H2 H3C 3
7. If required, re-write the formula according to the rules of bond-lines formulas. Organic Chemistry Pharmacy
ALKENES Hydrocarbons with ONE double bond C=C, that is, two C atoms have sp2 hybridizatation
general formula CnH2n
RULE Alkenes takes the name from the alkane with the same number of C atoms, replacing the ending "-ane" with ending"-ene"
When a hydrocarbon contains a p bond. it is called "unsaturated compound"
HOMO
2-methyl-2-heptene Organic Chemistry Pharmacy
The smallest alkene is made up by two C atoms
C2H4 CH2=CH2 ethene
C3H6 CH3-CH=CH2 propene
With a number of C atoms higher than three, the position of unsaturation is not unique CH -CH=CH-CH or CH -CH -CH=CH C4H8 3 3 3 2 2 C-C-C=C C-C=C-C butene ?
The two compounds are distinguished indicating the position of the double bond in the longest continuous chain of C atoms
1. The chain is so numbered as to give the lowest possible numbers to the double bond 2. The position of the double bond is indicated with the lowest of the two numbers of Cs involved in it Organic Chemistry Pharmacy
4 3 2 1 The number that indicates the CH3-CH2-CH=CH2 1-butene double bon position precedes the 4 3 2 1 alkene name, separated by a dash. CH3-CH=CH-CH3 2-butene
Compunds having the same carbon skeleton but differing for double bond position are called positional isomers.
C=C bond is the main feature of alkenes. Therefore, the parent chain must be the longest continuous chain of C atoms containing the double bond. 5 4 3 2 1 CH CH CH C CH 3 2 2 2 2-propyl-1-pentene CH2 CH2 CH3
(there is a 7 carbon chain, but it CH3 CH2 CH2 C CH2 DOES NOT CONTAIN the C=C bond) CH2 CH2 CH3 Organic Chemistry Pharmacy
Numbering must give the double bond the lowest possible number (even if this means giving a higher number to an alkyl substituent).
CH 3 4-methyl-2-pentene CH = CH3 CH CH CH3 NOT 2-methyl-3-pentene 5 4 3 2 1
It is not always possible to have the double bond in the chain from which the compound takes its name.
If the carbon-carbon double bond is a substituent, it takes as ending "-enyl" (ene for the double bound, yl for the free valence).
Since it is a substituent, the numbering must necessarily start from the C with which the substituent is linked to the main chain. The position of the double bond is determined accordingly. Organic Chemistry Pharmacy
4 3 2 1
CH3-CH2CH=CH- 1-butenyl 4 3 2 1
CH3-CH=CH-CH2- 2-butenyl 4 3 2 1 3-butenyl CH2=CHCH2CH2-
The IUPAC nomenclature still accepts trivial (non-systematic) names for largeòy usad groups:
CH2=CH- vinyl or ethenyl
3 CH2=CH-CH allyl o 2-propenyl (free valence on C sp )
CH3 examples: CH CH2
CH2 CH CH2 vinylcyclohexane 1-allyl-2-methylcyclobutane (ethenylcyclohexane) 1-methyl-2(2-propenyl)cyclobutane Organic Chemistry Pharmacy
Sometimes it is necessary to consider as a substituent a group linked with two valences (double bond) to the SAME C of the main chain .
The bivalent groups with the two valences on the same atom of C take the ending "-ilidene".
CH2= methylidene
CH3-CH= ethylidene propylidene CH3-CH2-CH=
examples: CH CH 3 CH CH2 CH3
CH3
ethylidenecyclohexane 1-methyl-2-propylidencyclopentane Organic Chemistry Pharmacy
CAUTION! Attentively consider the following differences:
CH2= two valences exchanged with the same C methylidene two valences exchanged with two different Cs methylene -CH2- (Attention: often methylidene is also called methylene: the use might generate confusion and should be avoided) Similarly:
CH3-CH= bivalent group with 2 valences on the same C ethylidene
-CH2-CH2- bivalent group with 2 valences on 2 different Cs ethylene
Bivalent groups with valences on the two Cs at the ends and a C sequence larger than two are indicated as a number of methylene groups
-CH2-CH2-CH2- trimethylene
-CH2-CH2-CH2-CH2- tetramethylene Organic Chemistry Pharmacy
ALKYNES Hydrocarbons with ONE triplele bond CºC, that is, two C atoms have sp2 hybridizatation
general formula CnH2n-2
RULE Alkynes takes the name from the alkane with the same number of C atoms, replacing the ending "-ane" with ending"-yne"
HOMO
2-octyne Organic Chemistry Pharmacy
The simpliest alkyne contains 2 C atoms
C2H2 HC CH Ethyne or Acetylene (trivial name)
CH C CH propyne C3H4 3
C H 4 6 CH3 C C CH3 or CH3 CH2 C CH C C C C C C C C butyne ?
The two compounds are distinguished indicating the position of the triple bond in the longest continuous chain of C atoms
1. The chain is so numbered as to give the lowest possible numbers to the triple bond 2. The position of the triple bond is indicated with the lowest of the two numbers of Cs involved in it Organic Chemistry Pharmacy
4 3 2 1 The number that indicates the CH3 CH2 C CH 1-butyne triple bon position precedes the alkyne name, separated by a dash. 4 3 2 1 2-butyne CH3 C C CH3 1-butyne e 2-butyne are positional isomers
CºC bond is the main feature of alkenes. Therefore, the parent chain must be the longest continuous chain of C atoms containing the triple bond. 6 5 4 3 2 1
CH3 CH2 CH2 CH C CH 3-propyl-1-hexyne CH2 CH2 CH3
(there is a chain with 7 Cs atoms, CH3 CH2 CH2 CH C CH but it DOES NOT CONTAIN C≡C) CH2 CH2 CH3 Organic Chemistry Pharmacy
Numbering must be done giving the triple bond the lowest possible number (even if this means giving a higher number to an alkyl substituent).
CH3 4-methyl-2-pentyne CH CH C C = 3 CH3 NOT 2-methyl-3-pentyne 5 4 3 2 1
If a substituent contains a carbon-carbon triple bond, the group takes the ending "-ynyl" (yne for the triple bond, yl for the free valence).
Since it is a substituent, the numbering must necessarily start from the C with which the substituent is linked to the main chain. The position of the double bond is determined accordingly.
4 3 2 1 H3C CH2C C 1-butynyl 4 3 2 1
H3C C C CH2 2-butynyl 4 3 2 1
HC C CH2 CH2 3-butynyl Organic Chemistry Pharmacy
HYDROCARBONS WITH MORE THAN ONE UNSATURATED BOND If in the hydrocarbon molecule there are two pairs of double bonds (i.e. 4 C sp2), the compound is called alka-diene or, more simply, diene.
RULE The nomenclature follows the rules of alkenes, indicating with a number the position of each double bond and entering the multiplicative prefix "di" before the ending "-ene".
The simplest diene contains 4 C atoms, with univocal position of double bonds: the numbers are superfluous and must be omitted.
CH2=CH-CH=CH2 butadiene
HOMO Organic Chemistry Pharmacy
3 7 8 5 3 4 6 10 8
2 9 1 7 2 2,7-decadiene
6 5 4 3 2 1 8 7 6 5 4 3 2 1 H3C C CHCH2CH=CH2 CH3CH2CH=CHCH2CH2CH=CH2 CH3 5-methyl-1,4-hexadiene 1,5-octadiene
2 4 6 8 3,6-nonadiene 1 3 5 7 9 When the two double bonds are consecutive (i.e if there is not any C between the two couple of sp2 C atomss) we speak of to conjugated diene
2 4 6 8 9 1 3 5 7 3,5-nonadiene conjugated Organic Chemistry Pharmacy
ATTENTION! Compounds with two consecutive double bonds are called allenes. sp2 sp2 In the dienes the unsaturated system is made of FOUR C atome (hybridized CH =C=CH allene sp2, while in the allene there a 2 2 sequence of THREE C atoms (hybridized sp2–sp-sp2). sp
If there are n pairs of C sp2 (and therefore n double bonds) we talk about polyenes. n = 3 triene n = 4 tetraene
The number of double bonds is indicated by the appropriate multiplicative prefix, before the ending -ene.
1 2 3 4 5 6 7 8 H C CH CH CH CH 1,4,7-octatriene 2 2 CH2 CH CH2 1 2 3 4 5 6 7 8
CH3CH=CH-CH=CH-CH=CH-CH3 2,4,6-octatriene conjugated Organic Chemistry Pharmacy
2 4 6 8 1 2 3 4 5 6 7 8
CH2=CH-CH=CH-CH=CH-CH=CH2 1 3 5 7 1,3,5,7-octatetraene conjugated If in the molecule there are two pairs of sp C (two triple bonds), we speak of alkadiyne (or diyne) and if in the hydrocarbon there is a double and a triple bond, we call it alkenynes or enynes (adding up the endings: ene + yne).
RULE If in the main chain there are double and triple bonds, the chain must be numbered so as to give the multiple bonds the lowest possible numbers. With the same numbering, the lowest number is for the double bond. Organic Chemistry Pharmacy
HC C C CH CH C C CH C CH butadiyne 3 2 1,4-hexadiyne
HC C CH CH 2 CH2 CH CH2 C CH butenyne 1-penten-4-yne 1 2 3 4 5 6 4-hexen-1-yne HC C CH2 CH CH CH3
1 2 3 4 5 6 7
CH3 C C CH2 CH CH CH3 7 6 5 4 3 2 1 correct numbering
2-epten-5-yne Organic Chemistry Pharmacy
SUMMARY OF RULES CONCERNING DUBLE AND TRIPLE BONDS The alkene takes its name from the alkane with the same number of atoms of C, replacing the ending "-ane" by the ending "-ene” If a substituent contains a double bond C=C, the group takes the ending "-enyl" (ene due to the double bond, yl because of the free valence) If there are two pairs of double bonds (i.e 4 C sp2), the compound is called alkadyene or, more simply, diene Compounds with two consecutive double bonds are not dienes, but allenes. Alkyne takes its name from the alkane with the same number of C atoms, replacing the ending "-ane" with the ending"-yne” If a substituent contains a triple C≡C bond, the group takes the ending “-ynyl" (yne for the triple bond, yl because of the free valence). If in the molecule there are two pairs of C sp (two triple bonds), we refer to alkadiyne (or diyne) and if there is a double and a triple bond in the hydrocarbon chain, we speak of alkenyne o enyne (it means that we link both the ending: ene + yne). Organic Chemistry Pharmacy
In molecules with more than one multiple bonds, the parent chain it is chosen on the basis of the following criteria, in the order : 1. The chain that contains the largest number of double or triple bonds.
5 4 3 2 2-butyl-1,3-pentadiene CH3 CH CH C CH2 CH2 CH2 CH3 (NOT 4-methylidene-2-octene) CH2 1
2. The chain that contains the largest number of C atoms.
7 6 5 4 3 2 1
CH3 C C CH CH2 CH CH2 4-vinyl-1-epten-5-yne (NOT 4-ethynyl-1,5-hexadiene) CH CH2 3. The chain that contains the largest number of double bonds.
3 4 5 6 HC C CH CH CH CH 2 2 3-ethynyl-1,5-hexadiene CH CH 2 (NOT 3-vinyl-5-hexen-1-yne) 2 1 Organic Chemistry Pharmacy
CYCLIC UNSATURATED HYDROCARBONS
RULE Unsaturated monocyclic hydrocarbons are named basing on the corresponding cycloalkane, replacing the ending -ane with the endings "-ene", "-diene”, "-triene", "-yne", "-diyne", etc., for one, two or three double bond or one, two or three triple bonds, respectively
Numbering must be done in such a way as to give the multiple bonds the lowest possible numbers. In a cycloalkene the numbers 1 and 2 necessarily go to the double bond, therefore the number is omitted. H C CH CH 2 H C CH 2 2 1 HC CH 1 2 2 2 2 2 1 H2C CH 2 HC CH 1 2 CH H C CH 1 2 CH 2 cyclobutene 2 cyclopentene cyclohexene In a cycloalkadiene the double bonds must be numbered, with the exception of the ring with five terms, where the numbers are obliged and, therefore, omitted. Organic Chemistry Pharmacy
5 2 1 4 2 1 1 3 5 etc. = = cyclopentadiene 2 3 5 4 4 3 3 3 2 4 2 4 1 1,3-cyclohexadiene 1 5 1,4-cyclohexadiene
Eventual alkyl substituents are indicated with the rules already seen with cycloalkanes. The position they occupy in the ring is determined by the double bond (which must have the numbers 1 and 2).
H3C CH 2 2 HC CH 2 C CH 1 1 HC CH CH CH CH H C CH CH 2 1 3 2 3 3 2 3 3-methylcyclobutene 3-ethyl-1-methylcyclopropene 2 HC CH 2 3 CH 3 3 4 1 CH HC CH 1 4 4 3 3 C CH 1-methyl-1,4-cyclohexadiene H C CH3 H3C 3 2 3 1 5,5-dimethylcyclopentadiene 5-methyl-1,3-cyclohexadiene