Question

The number of axial C-H bond(s) in the major product (P) of the given reaction is .............. 

Hint:

When determining axial bonds in cyclic compounds, consider the stereochemistry of the ring, especially if the reaction leads to a new chiral center.

Answer 1

Correct Answer: 5

Solution:

The given reaction involves the addition of a Grignard reagent, MeMgBr, to a ketone. The specific reaction is as follows:

1. The carbonyl group of the ketone undergoes nucleophilic attack by the methyl group from MeMgBr, forming an alkoxide intermediate.
2. Protonation of the alkoxide by H₃O⁺ yields the corresponding alcohol.

Given the cyclohexanone derivative with two tert-butyl groups:

• The methyl group from MeMgBr attacks the carbonyl carbon, leading to tert-butylcyclohexanol as the major product, where the alcohol group is equatorial and new methyl group axial.

We need to determine the number of axial C-H bonds in the major product. The cyclohexane ring in the major product has the following features:

• Each carbon in cyclohexane has one axial bond.
• Since the alcohol is equatorial, the added methyl group is axial.
• Total axial hydrogens are 5 (5 hydrogens on one side of the ring at axial positions).

Therefore, the number of axial C-H bonds in the major product is 5.

Conclusion: The number of axial C-H bonds is 5