Question

Extra practice: Compare reactivity between "thermal conditions" (controlled by temperature...not necessarily adding heat) and UV-light conditions. What is special about photochemistry for the first step of the reaction? (Hint: radicals next to double bonds, also called allylic radicals, are extremely stable!) In other words...draw mechanisms for each

Answer 1

The mechanism for themal Condition Cheat) is different from mechanism for uv light Condition condition could be written as The mechanism for thermal below addition syn I I H H Here double band attacks over bronne, H losshmorare Br (Reasonged from abone fig) substitution, The mechanism for uvron will be Br Br In af H BY I ho vist step institution Born Br+ Br ho - Both are free radical

and seep - propagation, Here Br can be writtenas Bri Bro attacks only at allylic position Stakes its hydrogen, free ralical because the allylic free radical) generated is hyhly stable due to de localization (en as given below So in case of heat, the mechanism will follow addition on mechanism. and in case of ur light, the mechanism will follow substitution son mechanism.