cvg In radical chlorination of alkanes, non-equivalent hydrogens react with chlo
ID: 691885 • Letter: C
Question
cvg 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 it Ais fomed twice as fast as B the A:B product ratio will be 2. Consider chlorination of the alkane below at 35 °C. I. Specify the most reactive C-H bond(s), a-c . Two noa-equivalent C-H bonds of comparable reactivity should be separated by conmas, ic ac 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. ie.a.c Submit Answer Retry Entire Group 4 more group attempts remalningExplanation / Answer
Radical chlorination of alkanes require the formation of a carbon radical site on the alkane, initiated by the photoinitator added to the reaction and the most stable radical site on the alkane proceeds to react best with the chlorine radical as only if the former lives long enough to encounter a chlorine radical, will it give a chlorinated alkane and sustain the reaction. The order of stability of carbon radicals are in the order methyl < primary < secondary < tertiary and the radical halogenation with chlorine is selective to alkane radical stability only to a certain extent unlike radical bromination due to the lower stability of chlorine radical. Therefore, among carbons labelled a to c, a is a tertiary carbon, b is a secondary carbon and c is a methyl carbon. Inferring from the stability mentioned previously, the reactivity of these sites can be ordered as a > b > c.
This makes the carbon site a the most reactive C-H bond followed by b and then finally c with sites a and b having comparable reactivity and c having the lowest reactivity.
From all the above it can now be observed that if a monochlorinated product is isolated, then from the reactivity differences and carbon radical stability, it definitely will be a product arising from the chlorination of site a.
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