Master Organic Chemistry Reaction Guide

Additions to alkenes accompanied by 1,2-hydride shifts

Description: When secondary (or primary) carbocations are formed, adjacent to a more substituted carbon, hydrogen atoms can shift. This leads to formation of a more stable carbocation.

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Comment section

14 thoughts on “Additions to alkenes accompanied by 1,2-hydride shifts

  1. Hey James, there’s a simple spelling error in the notes section under your examples. It reads, “Note that the first two examples show rearrangement to give mroe stable tertiary carbocations.”

  2. Does this result in 2 major products? One with the hydride shift and one without? Or does the hydride shift always happen if it can?

    1. If the hydride shift results in a more stable carbocation, then you can generally get it to go to the rearranged product, assuming that only one shift can happen. It’s not the easiest reaction to control so works best for simple cases.

  3. Hi James.

    For example 3, why is the Cl bonded to C3 and not C2. Is it due to the hydride Shift? If so why?
    Is it because although both C2 and C3 and secondary carbons, the R group bonded to C3 is a benzene (bigger and more stable group)?


    1. The benzylic carbocation (carbocation adjacent to benzene ring) is more stable than an ordinary secondary carbocation due to resonance stabilization.

  4. Will the predominant product be the hydride shift mechanism? How much more energetically favorable is this product?

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