Question

Consider the reaction sequence given below:

Which of the following statements is true?

• A. Changing the concentration of base will have no effect on reaction (1)
• B. Changing the concentration of base will have no effect on reaction (2)
• C. Changing the base from \(\mathrm{OH^-}\) to \(\mathrm{{}^-OR}\) will have no effect on reaction (2)
• D. Doubling the concentration of base will double the rate of both the reactions

Hint:

Reaction (1) has rate = k[t-BuBr] (SN1, first order in substrate only); reaction (2) has rate = k[t-BuBr][OH^-] (E2, depends on base).

Answer 1

The Correct Option is A

The scheme shows tert-butyl bromide reacting by two routes. Reaction (1), in OH^-/H₂O, gives t-BuOH with Rate = k[t-BuBr]. Reaction (2), in OH^-/C₂H₅OH, gives 2-methylpropene with Rate = k[t-BuBr][OH^-].
(1) The rate of reaction (1) does not contain [OH^-], so changing the base concentration has no effect on it. True.
(2) The rate of reaction (2) depends on [OH^-]. False.
(3) Changing the base from OH^- to RO^- (a stronger base) changes the E2 rate. False.
(4) Doubling [base] doubles only the rate of reaction (2), not that of reaction (1). False.
Answer: (1) Changing the concentration of base will have no effect on reaction (1)