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Question: How many pair(s) of geometrical isomers are possible with $C_6H_{12}$ (only in open chain structures...

How many pair(s) of geometrical isomers are possible with C6H12C_6H_{12} (only in open chain structures) (at room temperature):

A

2

B

3

C

4

D

5

Answer

4

Explanation

Solution

To determine the number of possible pairs of geometrical isomers for C6H12C_6H_{12} in open-chain structures, we list all possible alkene isomers and identify those exhibiting geometrical isomerism. Geometrical isomerism occurs when each carbon atom of the double bond is attached to two different groups.

The alkenes with geometrical isomerism are:

  1. 2-hexene: CH3−CH=CH−CH2−CH2−CH3CH_3-CH=CH-CH_2-CH_2-CH_3. This has one pair of isomers (cis and trans).
  2. 3-hexene: CH3−CH2−CH=CH−CH2−CH3CH_3-CH_2-CH=CH-CH_2-CH_3. This has one pair of isomers (cis and trans).
  3. 4-methyl-2-pentene: CH3−CH(CH3)−CH=CH−CH3CH_3-CH(CH_3)-CH=CH-CH_3. This has one pair of isomers (E and Z).
  4. 3-methyl-2-pentene: CH3−CH2−C(CH3)=CH−CH3CH_3-CH_2-C(CH_3)=CH-CH_3. This has one pair of isomers (E and Z).

Alkenes like 1-hexene, 2-methyl-1-pentene, 4-methyl-1-pentene, 2,2-dimethyl-1-butene, 2,3-dimethyl-1-butene, and 2,3-dimethyl-2-butene do not exhibit geometrical isomerism due to symmetry or the presence of identical groups on one of the double-bonded carbons.

Therefore, there are a total of 1+1+1+1=41 + 1 + 1 + 1 = 4 pairs of geometrical isomers possible.