Question

Change the following old names to new, post-names, and draw the structure of each compound: $\mathbf{\text{2,3-Dimethyl-1,3-cyclohexadiene}}$

Short answer

Name of the compound is:$\text{2,3-Dimethylcyclohexa-1,3-diene}$

Structure of the compound is:

Step-by-step solution

Step-by-Step SolutionStep 1: Changes in IUPAC naming in 1993

IUPAC changed their naming recommendations in 1993 to place the number indicating the position of the double bond immediately before the suffix -enenot before the parent name.

Naming of alkene

There are rules for naming alkene:

• Name the parent hydrocarbon: Look for the longest carbon chain having the double bond, then name the compound accordingly. The suffix –ene is used for alkenes

• Number the carbon atoms in the chain:Start numbering from the carbon nearer to the double bond but when the double bond is equidistant from both sides then start numbering from carbon nearer to the first branch point. So, double-bond carbons receive the lowest possible numbering.

• Write the full name:Number the substituents according to their positions in the chain, and write them in alphabetical order. The position of the double bond is indicated by the number of the first alkene carbon and placing that number directly before the parent name.

• If more than one double bond is present then use one of the suffixes as -diene, -triene,and so on based on a number of double bonds and indicate the position of each immediately before the suffix –ene.

• Cycloalkene is named the same way, but because there is no end so number the cycloalkene so double bond is taken between C1and C2. It is not necessary to indicate the position of the double bond in the name because it’s always between C1 and C2.

New IUPAC name

Based on above steps, name of the compound is $\text{2,3-Dimethylcyclohexa-1,3-diene}$.

Structure of given compound