Question

More polar solvents favour _____ reaction

E1

E2

E1CB

​

Answer 1

Answer:

E2♛┈⛧┈┈•༶.・゜゜・✧･ﾟ: *✧･ﾟ:*.・゜゜・༶•┈┈⛧┈♛

Answer 2

I read in a (book) that increasing the polarity of the solvent slightly reduces the rate of SN2 reaction. Why does this happen?

Increasing the polarity of the solvent increases the solvation of the nucleophile. There will be increased dipole-dipole interactions between a solvent and a nucleophile as polarity of the solvent increase.

This will reduce the mobility of the nucleophile and in turn reduce the rate of reaction in an SN2 reaction. The SN2 mechanism's rate is determined by the rate at which the nucleophile and the substrate can randomly collide into each other (in the right way - i.e. you want the nucleophile to attack the backside of the leaving group).

But I found in another book that the SN1 reaction rate increases in polar protic solvent. Why does this occur? The nucleophile still gets solvated right?

Yes, the nucleophile is still solvated, but in an SN1 reaction, the rate-determining step is the rate at which the leaving group leaves. That is by far the slowest step in an SN1 reaction because of the high activation energy involved in creating a carbocation, which is highly unstable. So it doesn't really matter if the nucleophile is heavily solvated or not so heavily solvated - the slowest step determines the rate.

Also, regarding why polar protic solvent increase the rate of SN1 reactions - think about the carbocation. There is a high activation energy barrier in forming this carbocation - it's extremely unstable. Protic solvents can stabilize this carbocation through hydrogen bond formation. This lowers the activation energy barrier.

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