Chapter 21, Problem 65A

Interpretation Introduction

Interpretation:

The difference betweencis - and trans - isomers should be described in terms of geometrical arrangement.

Concept introduction:

The molecule with same molecular formula and connectivity but differ in spatial arrangements of atoms in the molecule are said to be geometric isomers of each other.

Explanation of Solution

Geometric isomerism, or cis-trans, isomerism is most common in alkenes. The two forms exist due to no free rotation about carbon-carbon double bond. It exists only when the double bonded carbon atoms are joined to two different groups or atoms.

In cis- isomer, the two identical groups or atoms are close to each other whereas in trans- isomer two identical groups or atoms are farther apart.

For example:

The structures for cis -3-hexene and trans -3-hexene (hex represents the parent chain contains six carbon atoms and 3 represents the position of double bond in the chain) is: