A hydrocarbon X is optically. X upon hydrogenation gives an optically inactive alkane Y. Which of the following pair of compounds can be X and Y respectively?a)4-methyl-2-hexene and 3-methyl hexaneb)3-methyl-1-pentene and 3-methyl pentanec)4-methyl cyclopentene and methyl cyclopentaned)2-methyl-1-butene and 2-methyl butaneCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

The correct answer is Option B.
The optically active hydrocarbon X is 3-methyl-1-pentene CH₂=CH−CH(CH₃)CH₂CH₃. On catalytic hydrogenation, it forms 3-methyl pentane CH₃CH₂CH(CH₃)CH₂CH₃, which is optically inactive.

Answer

The optically active C6H12 hydrocarbon is 3-Methylpent-1-ene, having one chiral carbon shown in fig A.

On catalytic hydrogenation , the compound obtained is shown in fig B, and the molecule doesnot have chiral carbon.

The reaction is C6H12→C6H14 and this reaction takes place inthe presence of H2 and Pd.

Answer

Explanation:

Optical Activity:
Optical activity is the ability of a substance to rotate the plane of polarization of a beam of light. A substance is said to be optically active if it can rotate the plane of polarization of light. This property is due to the presence of chiral centers in the molecule. Chiral centers are carbon atoms that are bonded to four different groups.

Hydrogenation of Alkenes:
Hydrogenation is a chemical reaction in which hydrogen gas is added to an unsaturated compound, such as an alkene or alkyne, to form a saturated compound, such as an alkane. The reaction is typically carried out in the presence of a metal catalyst, such as platinum or palladium.

Optically Inactive Alkane:
An optically inactive compound is one that does not rotate the plane of polarization of light. This can occur when a compound has a plane of symmetry, meaning that it can be divided into two halves that are mirror images of each other. In other words, an optically inactive compound is achiral.

Analysis of Options:
Let's analyze each option to determine the correct pair of compounds.

a) 4-methyl-2-hexene and 3-methyl hexane:
4-methyl-2-hexene has a chiral center at the 4th carbon atom and is optically active. Hydrogenation of this compound will result in an alkane with a chiral center, making it optically active. Therefore, option a) is incorrect.

b) 3-methyl-1-pentene and 3-methyl pentane:
3-methyl-1-pentene has a chiral center at the 3rd carbon atom and is optically active. Hydrogenation of this compound will result in an alkane without a chiral center, making it optically inactive. Therefore, option b) is correct.

c) 4-methyl cyclopentene and methyl cyclopentane:
4-methyl cyclopentene has a chiral center at the 4th carbon atom and is optically active. Hydrogenation of this compound will result in a cyclopentane without a chiral center, making it optically inactive. Therefore, option c) is incorrect.

d) 2-methyl-1-butene and 2-methyl butane:
2-methyl-1-butene has a chiral center at the 2nd carbon atom and is optically active. Hydrogenation of this compound will result in an alkane with a chiral center, making it optically active. Therefore, option d) is incorrect.

Conclusion:
Based on the analysis above, the correct pair of compounds is option b) 3-methyl-1-pentene and 3-methyl pentane.

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