Organic Chemistry

Section 2.2 Nomenclature of Alkanes 67

First, determine the number of carbons

in the longest continuous chain.

Number the chain so that the

substituent gets the lowest possible

number.

PROBLEM 2

Which of the following can be used to verify that carbon is tetrahedral?

a. Methyl bromide does not have constitutional isomers.

b. Tetrachloromethane does not have a dipole moment.

c. Dibromomethane does not have constitutional isomers.

PROBLEM 3

Write a structure for each of the following compounds:

a. isopropyl alcohol d. neopentyl chloride

b. isopentyl fluoride e.tert-butylamine

c.sec-butyl iodide f. n-octyl bromide

2.2 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. The name that indicates the number of
   carbons in the parent hydrocarbon becomes the alkane’s “last name.”For exam-
   ple, a parent hydrocarbon with eight carbons would be called octane. The
   longest continuous chain is not always a straight chain; sometimes you have to
   “turn a corner”to obtain the longest continuous chain.


2. 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 sub-
   stituent’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.

CH 3 CHCH 2 CH 2 CH 3

CH 3

2-methylpentane 3-ethylhexane

4-isopropyloctane

1234 5

CH 3 CH 2 CH 2 CHCH 2 CH 3

CH 2 CH 3

654 321

CH 3 CH 2 CH 2 CHCH 2 CH 2 CH 2 CH 3

CHCH 3

CH 3

1234567 8

4-methyloctane 4-ethyloctane

4-propyloctane

CH 3 CH 2 CH 2 CH 2 CHCH 2 CH 2 CH 3

CH 3

three different alkanes with an

eight-carbon parent hydrocarbon

876543

321

21

CH 3 CH 2 CH 2 CH 2 CHCH 2 CH 3

CH 2 CH 2 CH 3

87654

CH 3 CH 2 CH 2 CHCH 2 CH 2 CH 3

CH 2 CH 2 CH 2 CH 3

4

56 78

32 1

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