Chapter 6, Problem 1PP

Interpretation Introduction

Interpretation:

The IUPAC names of the given compounds are to be determined.

Concept introduction:

The IUPAC name of alkyl halides consists of the name of the parent alkane with a prefix giving the name of the halogen along with its position. The prefixes used for halogens are chloro, fluoro, iodo, and bromo.

The longest carbon chain is numbered in a way so as to give a low numbering to the carbon with the halogen atom.

The substituents on the parent alkane are written alphabetically before the name of the parent alkane.

In cyclic compounds, the prefix ‘cyclo’ is used before the name of an alkane.

Substituents present on the same side of a ring are named with the prefix cis while those on opposite sides are named with the prefix‘trans’.

Answer to Problem 1PP

Solution:

$cis\text{-1-Bromo-2-methylcyclohexane}$

$cis\text{-1-Bromo-3-methylcyclohexane}$

$\text{2,3,5-Trimethylheptane}$

Explanation of Solution

a)

The parent alkane here is cyclohexane. The substituents are a bromine atom and a methyl group. Number the cyclohexane ring starting from the carbonwithbromine atom.

Putting the names of the substituents as the prefix alphabetically along with their positions before the name of the parent alkane, the IUPAC name can be written as $\text{1-Bromo-2-methylcyclohexane}$.

The two substituents are on the same side. Hence, the complete IUPAC name of the compound is

$cis\text{-1-Bromo-2-methylcyclohexane}$.

b)

The parent alkane here is cyclohexane. The substituents are a bromine atom and a methyl group. Number the cyclohexane ring starting from the carbon with the bromine atom. Both the bromine group and the methyl group are in equatorial position.

Putting the names of substituents as the prefix alphabetically along with their positions before the name of the parent alkane, the name can be written as $\text{1-Bromo-3-methylcyclohexane}$.

The two substituents are equatorial at the $1,3$position. So, they have the cis configuration.

Hence, the complete IUPAC name of the compound is $cis\text{-1-Bromo-3-methylcyclohexane}$.

c)

Select the longest continuous carbon chain and number it from that end, giving the lower number to the substituents.

The parent chain has seven carbon atoms. Thus, the parent alkane is heptane. There are three methyl substituents at $\text{C-2,C-3,C-4}$.

Hence, the IUPAC name of the compound is $\text{2,3,5-Trimethylheptane}$.