Can E2 reactions be reversible?

A lot of E2 reactions I have seen are irreversible. Is this true in general?

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(Image source: Organic Chemistry 11e by Solomons)

I tried to reason this using the following argument; The transition state requires the base, the $\beta$-hydrogen, $\alpha,\beta$-carbons, and the leaving group to be simultaneously co-planar. In the forward direction, it is usually possible due to the stability of the staggered conformation. In the reverse, we would require both the leaving group and the conjugate acid of the base to become simultaneously co-planar with the double bond, which would have nearly $0$ probability.

Is this reasoning correct? Or is there an example of a reversible E2 reaction?

  • 1
    $\begingroup$ An objective way of quantifying reversibility is simply to take a look at the values of the equilibrium constants for such elimination reactions. $\endgroup$ Jul 6, 2020 at 9:00
  • 2
    $\begingroup$ The principle reason why it's at least rare in the reverse direction is that, by microscopic reversibility, you would have a transition state with three components, decreasing the likelihood of forming the transition state for entropic reasons. Whether or not it's true in general is difficult to say, since enzymatic processes may overcome the previous point. $\endgroup$
    – Zhe
    Jul 6, 2020 at 14:06
  • $\begingroup$ @Zhe so can we say that non-enzymatic E2 processes are irreversible in general? $\endgroup$ Jul 7, 2020 at 3:31
  • $\begingroup$ The E2 does only have one transition state, however, the energy required to move in the reverse direction for it is quite large. $\endgroup$ Jul 7, 2020 at 13:30
  • $\begingroup$ In general, sure. $\endgroup$
    – Zhe
    Jul 7, 2020 at 14:44


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