FUNCTIONAL GROUPS AND NOMENCLATURE

1 FUNCTIONAL GROUPS

• A functional group is a portion of an organic molecule which consists of atoms other than carbon and hydrogen, or which contains bonds other than C–C and C–H bonds. For example, ethane (Fig 1a) is an alkane and has no functional group. All the atoms are carbon and hydrogen and all the bonds are C–C and C–H. Ethanoic acid (Fig 1b) on the other hand has a portion of the molecule which contains atoms other than carbon and hydrogen, and bonds other than C—H and C—C. This portion of the molecule is called a functional group – • in this case a carboxylic acid.

2 Functional Groups

3 Common functional groups

• The following are some of the more common functional groups in organic chemistry.

• These are rarely classified as functional groups

4 Common functional groups

5 Common functional groups

6 Common functional groups

7 NOMENCLATURE

• Nomenclature of alkanes • Alkanes are composed of only carbon atoms and hydrogen atoms and contain only single bonds. Compounds that contain only carbon and hydrogen are called hydrocarbons, so an alkane is a hydrocarbon that has only single bonds. Alkanes in which the carbons form a continuous chain with no branches are called straight-chain alkanes.

8 Alkanes

• As the number of carbons in an alkane increases beyond three, the number of possible structures increases. There are two possible structures for an alkane with molecular formula In addition to butane—a straight-chain alkane—there is a branched butane called isobutane. Both of these structures fulfill the requirement that each carbon forms four bonds and each hydrogen forms only one bond.

9 Alkanes

• Compounds such as butane and isobutane that have the same molecular formula but differ in the order in which the atoms are connected are called constitutional isomers—their molecules have different constitutions. In fact, isobutane got its name because it is an “iso”mer of butane. The structural unit—a carbon bonded to a hydrogen and two groups—that occurs in isobutane has come to be called “iso.” Thus, the name isobutane tells you that the compound is a four- carbon alkane with an iso structural unit.

10 Alkanes

11 Alkanes

• There are three alkanes with molecular formula Pentane is the straightchain alkane. Isopentane, as its name indicates, has an iso structural unit and five carbon atoms. The third isomer is called neopentane. The structural unit with a carbon surrounded by four other carbons is called “neo.”

12 Alkanes

13 Alkanes

• There are five constitutional isomers with

molecular formula C6H14

14 Alkanes • There are nine alkanes with molecular formula C7H16 • Notice that neoheptane cannot be used as a name because three different heptanes have a carbon that is bonded to four other carbons and a name must specify only one compound. • The number of constitutional isomers increases rapidly as the number of carbons in an alkane increases. For example, there are 75 alkanes with molecular formula C10H22

15 Alkanes

16 17 18 IUPAC nomenclature

• This method of nomenclature is called systematic nomenclature. It is also called IUPAC nomenclature because it was designed by a commission of the International Union of Pure and Applied Chemistry (abbreviated IUPAC and pronounced “eye-youpack”) at a meeting in Geneva, Switzerland, in 1892. The IUPAC rules have been continually revised by the commission since then. Names such as isobutane and neopentane—nonsystematic names—are called common names

19 Nomenclature of Alkyl Substituents

• Removing a hydrogen from an alkane results in an alkyl substituent (or an alkyl group). Alkyl substituents are named by replacing the “ane” ending of the alkane with “yl.” The letter “R” is used to indicate any alkyl group.

20 Nomenclature of Alkyl Substituents

• If a hydrogen of an alkane is replaced by an OH, the compound becomes an alcohol; if it is replaced by an the compound becomes an amine; and if it is replaced by a halogen, the compound becomes an alkyl halide.

21 Nomenclature of Alkyl Substituents

• An alkyl group name followed by the name of the class of the compound (alcohol, amine, etc.) yields the common name of the compound. The following examples show how alkyl group names are used to build common names:

22 Nomenclature of Alkyl Substituents

• Two alkyl groups—a propyl group and an isopropyl group—contain three carbon atoms. A propyl group is obtained when a hydrogen is removed from a primary carbon of propane. A primary carbon is a carbon that is bonded to only one other carbon. An isopropyl group is obtained when a hydrogen is removed from the secondary carbon of propane. A secondary carbon is a carbon that is bonded to two other carbons. Notice that an isopropyl group, as its name indicates, has its three carbon atoms arranged as an iso structural unit.

23 Nomenclature of Alkyl Substituents

24 Nomenclature of Alkyl Substituents

• There are four alkyl groups that contain four carbon atoms. The butyl and isobutyl groups have a hydrogen removed from a primary carbon. A sec-butyl group has a hydrogen removed from a secondary carbon (sec-, often abbreviated s-, stands for secondary), and a tert-butyl group has a hydrogen removed from a tertiary carbon (tert-, sometimes abbreviated t-, stands for tertiary). A tertiary carbon is a carbon that is bonded to three other carbons. Notice that the isobutyl group is the only group with an iso structural unit.

25 Nomenclature of Alkyl Substituents

26 Nomenclature of Alkyl Substituents

• A name of a straight-chain alkyl group often has the prefix “n” (for “normal”), to emphasize that its carbon atoms are in an unbranched chain. If the name does not have a prefix such as “n” or “iso,” it is assumed that the carbons are in an unbranched chain.

27 Nomenclature of Alkyl Substituents

• Like the carbons, the hydrogens in a molecule are also referred to as primary, secondary, and tertiary. Primary hydrogens are attached to primary carbons, secondary hydrogens to secondary carbons, and tertiary hydrogens to tertiary carbons.

28 Nomenclature of Alkanes • The systematic name of an alkane is obtained using the following rules: • 1. Determine the number of carbons in the longest continuous carbon chain. This chain is called the parent hydrocarbon.

29 TWO

• The name of any alkyl substituent that hangs off the parent hydrocarbon is cited before the name of the parent hydrocarbon, together with a number to designate the carbon to which the alkyl substituent is attached. The chain is numbered in the direction that gives the substituent as low a number as possible. The substituent’s name and the name of the parent hydrocarbon are joined in one word, and there is a hyphen between the number and the substituent’s name.

30 Number the chain so that the substituent gets the lowest possible number.

31 THREE

• If more than one substituent is attached to the parent hydrocarbon, the chain is numbered in the direction that will result in the lowest possible number in the name of the compound. The substituents are listed in alphabetical (not numerical) order, with each substituent getting the appropriate number. In the following example,the correct name (5-ethyl-3- methyloctane) contains a 3 as its lowest number,while the incorrect name (4-ethyl-6- methyloctane) contains a 4 as its lowest number:

32 THREE • If two or more substituents are the same, the prefixes “di,”“tri,” and “tetra” are used to indicate how many identical substituents the compound has.

33 THREE

• The prefixes di, tri, tetra, sec, and tert are ignored in alphabetizing substituent groups, but the prefixes iso, neo, and cyclo are not ignored.

34 FOUR • When both directions lead to the same lowest number for one of the substituents, the direction is chosen that gives the lowest possible number to one of the remaining substituents.

35 FIVE

• If the same substituent numbers are obtained in both directions, the first group cited receives the lower number.

36 SIX

• If a compound has two or more chains of the same length, the parent hydrocarbon is the chain with the greatest number of substituents

37 NOTE

• In a compound such as 4-(1- methylethyl)octane, the substituent name is in parentheses; the number inside the parentheses indicates a position on the substituent, whereas the number outside the parentheses indicates a position on the parent hydrocarbon.

38 EXAMPLES

39 EXAMPLES

40 Nomenclature of Cycloalkanes

• Cycloalkanes are alkanes with their carbon atoms arranged in a ring. Because of the ring, a cycloalkane has two fewer hydrogens than an acyclic (noncyclic) alkane with the same number of carbons. This means that the general molecular formula for a cycloalkane is Cycloalkanes are named by adding the prefix “cyclo” to the alkane name that signifies the number of carbon atoms in the ring.

41 EXAMPLES

42 Cycloalkanes

• Cycloalkanes are almost always written as skeletal structures. Skeletal structures show the carbon–carbon bonds as lines, but do not show the carbons or the hydrogens bonded to carbons.

43 Acyclic molecules

• Acyclic molecules can also be represented by skeletal structures. In a skeletal structure of an acyclic molecule, the carbon chains are represented by zigzag lines. Again, each vertex represents a carbon, and carbons are assumed to be present where a line begins or ends.

44 Acyclic molecules

45 The rules for naming cycloalkanes • They resemble the rules for naming acyclic alkanes: 1. In the case of a cycloalkane with an attached alkyl substituent, the ring is the parent hydrocarbon unless the substituent has more carbon atoms than the ring. In that case, the substituent is the parent hydrocarbon and the ring is named as a substituent. There is no need to number the position of a single substituent on a ring.

46 The rules for naming cycloalkanes

47 The rules for naming cycloalkanes

• If the ring has two different substituents, they are cited in alphabetical order and the number 1 position is given to the substituent cited first.

48 The rules for naming cycloalkanes

• If there are more than two substituents on the ring, they are cited in alphabetical order. The substituent given the number 1 position is the one that results in a second substituent getting as low a number as possible. If two substituents have the same low number, the ring is numbered—either clockwise or counterclockwise—in the direction that gives the third substituent the lowest possible number. For example, the correct name of the following compound is 4-ethyl- 2-methyl1-propylcyclohexane, not 5-ethyl-1-methyl-2- propylcyclohexane:

49 The rules for naming cycloalkanes

50 Nomenclature of Alkyl Halides

• Alkyl halides are compounds in which a hydrogen of an alkane has been replaced by a halogen. Alkyl halides are classified as primary, secondary, or tertiary, depending on the carbon to which the halogen is attached. Primary alkyl halides have a halogen bonded to a primary carbon, secondary alkyl halides have a halogen bonded to a secondary carbon, and tertiary alkyl halides have a halogen bonded to a tertiary carbon

51 Nomenclature of Alkyl Halides

52 Nomenclature of Alkyl Halides

• The common names of alkyl halides consist of the name of the alkyl group, followed by the name of the halogen—with the “ine” ending of the halogen name replaced by “ide” (i.e., fluoride, chloride, bromide, iodide).

53 Nomenclature of Alkyl Halides • In the IUPAC system, alkyl halides are named as substituted alkanes. The substituent prefix names for the halogens end with “o” (i.e., “fluoro,”“chloro,”“bromo,”“iodo”). Therefore, alkyl halides are often called haloalkanes.

54 Nomenclature of Ethers

• Ethers are compounds in which an oxygen is bonded to two alkyl substituents. If the alkyl substituents are identical, the ether is a symmetrical ether. If the substituents are different, the ether is an unsymmetrical ether.

55 Nomenclature of Ethers

• The common name of an ether consists of the names of the two alkyl substituents (in alphabetical order), followed by the word “ether.” The smallest ethers are almost always named by their common names.

56 Nomenclature of Ethers

57 Nomenclature of Ethers

• The IUPAC system names an ether as an alkane with an RO substituent. The substituents are named by replacing the “yl” ending in the name of the alkyl substituent with “oxy.”

58 Nomenclature of Ethers

59 Nomenclature of Alcohols • Alcohols are compounds in which a hydrogen of an alkane has been replaced by an OH group. Alcohols are classified as primary, secondary, or tertiary, depending on whether the OH group is bonded to a primary, secondary, or tertiary carbon—the same way alkyl halides are classified.

60 Nomenclature of Alcohols

• The common name of an alcohol consists of the name of the alkyl group to which the OH group is attached, followed by the word “alcohol.”

61 Nomenclature of Alcohols • The functional group is the center of reactivity in a molecule. In an alcohol, the OH is the functional group. The IUPAC system uses a suffix to denote certain functional groups. The systematic name of an alcohol, for example, is obtained by replacing the “e” at the end of the name of the parent hydrocarbon with the suffix “ol.”

62 Nomenclature of Alcohols • When necessary, the position of the functional group is indicated by a number immediately preceding the name of the alcohol or immediately preceding the suffix. The most recently approved IUPAC names are those with the number immediately preceding the suffix.

63 Nomenclature of Alcohols

• The following rules are used to name a compound that has a functional group suffix: 1. The parent hydrocarbon is the longest continuous chain containing the functional group. • The parent hydrocarbon is numbered in the direction that gives the functional group suffix the lowest possible number.

64 Example

65 Nomenclature of Alcohols

• If there is a functional group suffix and a substituent, the functional group suffix gets the lowest possible number.

66 Nomenclature of Alcohols

• If the same number for the functional group suffix is obtained in both directions, the chain is numbered in the direction that gives a substituent the lowest possible number. Notice that a number is not needed to designate the position of a functional group suffix in a cyclic compound, because it is assumed to be at the 1-position.

67 Nomenclature of Alcohols

68 Nomenclature of Alcohols

• If there is more than one substituent, the substituents are cited in alphabetical order.

69 Nomenclature of Amines

• Amines are compounds in which one or more of the hydrogens of ammonia have been replaced by alkyl groups. Smaller amines are characterized by their fishy odors. Fermented shark, for example, a traditional dish in Iceland, smells exactly like triethylamine.

70 Nomenclature of Amine • There are primary amines, secondary amines, and tertiary amines. The classification depends on how many alkyl groups are bonded to the nitrogen. Primary amines have one alkyl group bonded to the nitrogen, secondary amines have two, and tertiary amines have three.

71 Nomenclature of Amine • The common name of an amine consists of the names of the alkyl groups bonded to the nitrogen, in alphabetical order, followed by “amine.” The entire name is written as one word (unlike the common names of alcohols, ethers, and alkyl halides, in which “alcohol,”“ether,” and “halide” are separate words).

72 Examples

73 Nomenclature of Amine

• Nitrogen compounds with four alkyl groups bonded to the nitrogen—thereby giving the nitrogen a positive formal charge—are called quaternary ammonium salts. Their names consist of the names of the alkyl groups in alphabetical order, followed by “ammonium” (all in one word), and then the name of the counterion as a separate word.

74 Nomenclature of Amine

75 Reference Textbooks

• Organic Chemistry Clayden • Organic Chemistry Klein • Organic Chemistry Paula Bruice

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