Question

Why does the rate of the E1 reaction depend only on the substrate?

Answer 1

Step 1 is the rate determining step (slow step) and therefore, we have only one reactant which is `R-X` and the `Rate = k[R-X]`.

Explanation:

The elimination reaction E1 from its name, the 1 means that it is a unimolecular reaction.

E1 reactions happen in two consecutive steps:

Step 1: Formation of the carbocation (`R-X` is the alkyl halide).
`" " " " " "` `R-X -> R^+ + X^-`

Step 2: Attack of the nucleophile.
`" " " " " "` `R^+ + Nu^(-) -> R' + HNu` where `R'` is an alkene.

Since the first step is bond breaking (needs energy) and the second step is bond formation (releases energy), therefore, step 1 is the rate determining step (slow step) and therefore, we have only one reactant which is `R-X` and the `Rate = k[R-X]`.

Here is a video about E1 and E2.