FUNCTIONAL GROUPS AND NOMENCLATURE, Exams of Organic Chemistry

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FUNCTIONAL GROUPS

AND NOMENCLATURE

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.

Common functional groups

• The following are some of the more common

functional groups in organic chemistry.

• These are rarely classified as functional groups

Common functional groups

Common functional groups

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.

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.

Alkanes

Alkanes

Alkanes

• There are five constitutional isomers with

molecular formula C 6 H 14

Alkanes

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

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.