Question

1. What is considered the slow step in an SN 1 reaction? 2. Compare the number of moles of t-butyl alcohol used in this experiment with the number of moles of HCl used. a. How many moles of excess HCI were used? b. What is the minimum number of mL of concentrated HCl that could be used to react with all of the t-butyl alcohol? Concentrated HClis 12M. 3. Why can't Sn 1 and Sn2 reactions of alcohols take place at neutral or basic pH?

Answer 1

SN1 reactions are called unimolecular nucleophilic substitution reactions. That means the rate of reaction depends upon only on Substrate concentration, and not on the concentration of the nucleophile.

This reaction proceeds through two steps:

1. Formation of carbocation intermediate after the departure of leaving group. Actually the bond between the carbon atom and the leaving group breaks to produce a carbocation. The polar solvent favors this step.
2. Attack of the nucleophile on the electron deficient carbocation (formed in step 1) to form corresponding substituted product

The first step is considered slow step because formation of cation is slow, the subsequent step occurs rapidly. The first step is the rate determining step as it is slow step. In first step only substrate is present at transition state, hence it is unimolecular. The rate of reaction depends upon only on Substrate concentration, and not on the concentration of the nucleophile.