In radical chlorination of alkanes, non-equivalent hydrogens react with chlorine

Question

In radical chlorination of alkanes, non-equivalent hydrogens react with chlorine atoms at different rates. At 35 °C, primary, secondary, and tertiary C-H bonds react at relative rates of 1:3.9:5.2 respectively. These are conditions of kinetic control where product ratios are determined by relative rates of formation. For example, if A is formed twice as fast as B, the A:B product ratio will be 2 Consider chlorination of the alkane below at 35 °C. 1. Specify the most reactive C-H bond(s), a-c. Two non-equivalent C-H bonds of comparable reactivity should be separated by commas, i.e. a,c. 2. Specify the site of chlorination in the major monochloro substitution product, a-c. Two products that form in comparable quantities should be separated by commas, i.e. a,c

Explanation / Answer

Solution:- ( A ) Most reactive CH bond is "B"

Site of chlorination in major monochloro substitution product is "B"

Reason:- B is tertiary position and A is primary position and as given in the question tertiary position is very much more reactive than primary, due to stabilization by hyperconjugation so that's why B is the most reactive bond as well as major substitution product.

(B) In this problem, we have three type of position A- primary, B-secondary, C-quaternary. quaternary carbon doesn't have any hydrogen so it will not be the site for substitution product so it can not be the major product.

Most reactive CH bond is "B"

The site of chlorination in major monochloro substitution product is "B".

Reason:- Because in comparison of primary and secondary is more reactive due to stabilization of secondary radical by hyperconjugation.

stability by hyperconjugation tertiary > secondary > primary (least stable hence least reactive)

tertiary is most stable due to the highest number of hyperconjugation structure because of the greater number of alpha hydrogen then secondary and then primary.

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