In general, two factors contribute to the ratio of products in a photohalogenati
ID: 505322 • Letter: I
Question
In general, two factors contribute to the ratio of products in a photohalogenation:(a) the number of hydrogen atoms that can react to yield a given product(b) the inherent reactivities of the different hydrogen atoms. Thus, for instance, if both kinds of hydrogen had the same intrinsic reactivity, propane would yield a 3:1 ratio of 1-bromopropane and 2-bromopropane upon bromination (75% the former, 25% the latter). Similarly, if the protons on the chlorine-bound carbon were nine times as reactive as the hydrogens on the fluorine-bound carbon in bromination, 1-chloro-2-fluoroethane would yield a 9:1 ratio of 1-bromo-1-chloro-2-fluoroethane to 1-bromo-2-chloro-1-fluoroethane (90% the former, 10% the latter). How much more reactive is the 3 degree C-H hydrogen than the 1 degree CH_3 hydrogens in the chlorination reaction shown below? This is a question about the "intrinsic reactivity" factor. (Products: 36% 2-chloro-2-methylpropane, 64% 1-chloro-2-methylpropane).Explanation / Answer
The reactivity of tertiary H to the primary H = % of tertairy halide / % of primary halide
= 36/64
=0.5625