Q 3-3-55 E - Organic Chemistry (Mcmurry)

Question

We’ll see in the next chapter that there are two isomeric substances, both named 1,2-dimethylcyclohexane. Explain.

Step-by-Step Solution

Answer

By differentiating on the basis of the cis and trans arrangement.

IUPAC nomenclature

It is method to give scientific name to the organic compounds recommended by the Indian Union of Pure and Applied Chemistry.

Nomenclature of cycloalkanes

IUPAC rules used for naming of cycloalkanes

• Name the parent cycloalkane 
• Assign numbering to the substituents
• Assign the first number to the bulky group
• Halogens get the first priority
• If both the substituent are on wedge or dash then the cis prefix is used
• If one substituent on the wedge and the other on the dash and vice-versa then the trans prefix is used
• Write the name of the molecule in alphabetic

Nomenclature of 1,2 dimethyl cyclohexane

The two isomer formed of 1,2 dimethyl cyclohexane is differentiated by the arrangement of the substituent on wedge and dash.

If both the methyl group are on wedge or dash then the cis prefix is used.

If one of the methyl groups is on the wedge and the other on das then the trans prefix is used as shown below:

                        Cis

                         Trans