Question

Give a basic idea about IUPAC nomenclature system and comment on IUPAC names of straight chain alkanes.

Answer 1

i. International Union of Pure and Applied Chemistry (IUPAC) was founded (in 1919) and a systematic method of nomenclature for organic compounds was developed under its banner

ii. This was done because of growing number of organic compounds with increasingly complicated structures and it was difficult to name them. To simplify and avoid confusions, IUPAC system is accepted and widely used all over the world today. According to this system, a unique name is given to each organic compound.

Following things are taken into consideration while naming a particular organic compound:

• To arrive at the IUPAC name of an organic compound, its structure is considered to be made of three main parts: parent hydrocarbon, branches and functional groups.
• The IUPAC names of a compound are obtained by modifying the name of its parent hydrocarbon further incorporating names of the branches and functional groups as prefix and suffix.

IUPAC names of straight chain alkanes: a. The homologous series of straight chain alkanes forms the parent hydrocarbon part of the IUPAC names of aliphatic compounds. 

b. The IUPAC name of a straight chain alkane is derived from the number of carbon atoms it contains. 

c. IUPAC names of the first twenty alkanes are mentioned in the following table:

Number of carbons	Molecular formula	Condensed formula	IUPAC name
1	CH4	CH4	Methane
2	C2H6	CH3-CH3	Ethane
3	C3H8	CH3-(CH2)2-CH3	Propane
4	C4H10	CH3-(CH2)2-CH3	Butane
5	C5H12	CH3-(CH2)3-CH3	Pentane
6	C6H14	CH3-(CH2)4-CH3	Hexane
7	C7H16	CH3-(CH2)5-CH3	Heptane
8	C8H18	CH3-(CH2)6-CH3	Octane
9	C9H20	CH3-(CH2)7-CH3	Nonane
10	C10H22	CH3-(CH2)8-CH3	Decane
11	C11H24	CH3-(CH2)9-CH3	Undecane
12	C12H26	CH3-(CH2)10-CH3	Dodecane
13	C13H28	CH3-(CH2)11-CH3	Tridecane
14	C14H30	CH3-(CH2)12-CH3	Tetradecane
15	C15H32	CH3-(CH2)13-CH3	pentadecane
16	C16H34	CH3-(CH2)14-CH3	Hexadecane
17	C17H36	CH3-(CH2)15-CH3	Heptadecane
18	C18H38	CH3-(CH2)16-CH3	Octadecane
19	C19H40	CH3-(CH2)17-CH3	Nonadecane
20	C20H42	CH3-(CH2)18-CH3	Icosane