Account for the following observations :
(a) `t-BuF` is solvolysed only in very acidic solution.
(b) `t-BuC1` is solvolysed more slowly than 2-chloro-2,3,3,-trimethy1-butane (A).
(c) `t-BuC1` is solvolysed much faster than 2-chloro-1,1,1-trifluoro-2-methy1 propane (B).
(d) `t-BuC1` is solvolysed more slowly in `90 % D_2 O - 10 %` dioxane than in `90 % H_2 O - 10 %` dioxane solution.

Explanation

(a) `F^(Ө)` is poor leaving group, but H-bonding with a strong acid encourages its departure (called electrophilic catalysis).
(b)
The formation of (B) reduces some some of the steric crowding in (A) induced by two `Me` atoms and the t-Bu group on `alpha-C` atom. This is an example of steric acceleration.
(c) `F_(3)-overset(Me)overset(|)(CH^(o+))` is destabilised by the strongly `overline (e)- "withdrawing" (F_3C)` group, making the solvolysis of (B) slower.
(d) D-bonds are not as stabilising as H-bonds. In otehr words, `H_2 O` is a more polar solvent than `D_2 O` and being so, increases the rate of the `SN^1` solvolysis.