Question

Select the correct name for the following compound, including the correct (E) or (Z) designation where appropriate.

• (E) 2,5-dimethyl-2-hexene 

• 2,4-dimethyl-4-hexene 

• (Z) 2,5-dimethyl-2-hexene 

• 2,5-dimethyl-2-hexene

Answer 1

Concepts and reason

The skeletal structures of an alkene is given and its systematic name or IUPAC names along with E/Z configuration need to be given. Follow the IUPAC nomenclature for alkenes by first selecting the correct parent chain and numbering the substituents by giving priority to the alkene and thus obtaining the required systematic name.

Fundamentals

Skeletal structure: The skeletal formula represents the bonding of different atoms with each other and shows the basic skeleton of the molecule.

Systematic/IUPAC name: In an IUPAC name, the substituents attached serve as the prefix to the parent chain and the functional groups serve as the suffix of the parent chain. Therefore, IUPAC name is written as follows:

Substituents + parent chain + functional group

Parent chain: The number of carbon atoms in the longest chain present form the parent chain.

Functional groups: The groups responsible for the characteristic chemical properties of a molecule are known as functional groups. Some examples of functional include carboxylic acids, ketones etc.

Substituents: All the atoms or groups other than functional groups are known as substituents

Rules for naming an alkene:

• Select the longest possible carbon chain (parent chain) including the double bond.

• Use the suffix ‘ene’ for the parent chain in case of an alkene.

• Number the carbon atoms possessing the double bond in such a way that the double bond gets least number.

• In case of presence of more than one double bond, the respective position of the double bonds is indicated. Also, the number of bonds are indicated as follows:

diene- for two double bonds,

triene- for three double bonds and so on.

• If the compound is cyclic, then the prefix ‘cyclo’ is attached to the parent chain.

The parent chain in the given compound is the 6-carbon chain as shown below:

The name of the compound is 2,5-dimethyl-2-hexene.

Ans: