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.
This page is available to MOC Members only.
Sign up here for about 30 cents/ day!
Can you add the pushing arrows to the first examples? They’re always on my quiz.
Yes I can do that!! Thanks for the suggestion
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.”
Fixed, thanks for the spot Matthew!
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?
Thanks
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.
Is it possible to have consecutive hydride shifts?
It certainly is, although for our purposes we generally keep it to one. One fun example of multiple shifts is found in the biosynthesis of lanosterol from squalene. https://en.wikipedia.org/wiki/Lanosterol
Thank you for this!!! Explaining the mechanism makes so much more sense.
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)?
Thanks.
The benzylic carbocation (carbocation adjacent to benzene ring) is more stable than an ordinary secondary carbocation due to resonance stabilization.
Will the predominant product be the hydride shift mechanism? How much more energetically favorable is this product?
Thanks!
hey James I think you made a mistake with the description reaction, a third R group was added to the product
Thank you Raj.