VIl. (20 pts) For each of the following pairs of reactions, indicate which will
ID: 1036326 • Letter: V
Question
VIl. (20 pts) For each of the following pairs of reactions, indicate which will be faster (a or b or neither) and briefly explain why. Which mechanism occurs? No explain no credit. CH3SNa Cl SCH3 H20o ether OTs ?? b. CI CH3SNa SCH3 b. CH3 H2o CH3 ether OTs OH mechanism name? I mechanism name? which is faster (a, b or neither)? explain which is faster (a, b or neither)? explain a. OH HI Br CHOH // /???? Nal b. CHOH b. OH Br OCH3 mechanism name? which is faster (a, b or neither)? explain mechanism name? which is faster (a, b or neither)? explainExplanation / Answer
VII. Reaction rates and mechanism
First set : top left
Mechanism : Sn2
Faster = b
In Sn2, concerted mechanism, the steric crowding at the carbon having the leaving group plays a major role. As the steric crowding goes up (as in b to a above), the Sn2 reaction rate decreases due to high energy demand for the T.S. formed. Therefore, b with lower steric crowding will give faster reaction.
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Second set : top right
Mechanism : Sn1
Faster = a
In Sn1, stability of carbocation formed in the first step (rate determining step) plays a major role. So as the stability of carbocation formed from a, is higher than b. The reaction rate for a is also higher.
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First set : bottom left
Mechanism : Sn2
Faster = a
In a, the -OH is converted into a good leaving group by protonation from acid HI and therefore the rate of reaction is higher. -OH is a bad leaving group.
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Second set : bottom right
Mechanism : Sn1
Faster = b
In Sn1, stability of carbocation formed in the first step (rate determining step) plays a major role. So as the stability of carbocation formed from b, is higher than a. The reaction rate for b is thus higher.
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