Wize University Organic Chemistry Textbook > Electrophilic Addition Reactions to Alkenes/Alkynes
Carbocation Rearrangements
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Carbocation Rearrangements
Carbocations are carbon atoms that carry a positive charge. They are formed when a leaving group departs (see the SN1, SN2, E1 and E2 reaction!) or when an alkene acts as a nucleophile.
- carbocations that are more substituted are more stable (tertiary > secondary > primary >>> methyl)
- carbocations can also be stabilized by resonance (i.e. vinylic and allylic)
Carbocation Rearragements
Sometimes, carbocations will rearrange in order to produce a more stable form. This can happen a few different ways with two being the most common:
- a 1,2-hydride shift
- a 1,2-methyl shift
Watch Out!
The important thing to know about these rearragements is that they lead to the production of multiple products! This is important to know when you are asked to draw the products of reactions and need to be accounted for when drawing mechanisms.
Wize Tip
Whenever you have a reaction that generates a carbocation, stop and ask yourself "is this the best carbocation, or can it be better?". If the answer is "no" - keep going! If the answer is "yes", draw the rearrangement and then predict the products from both the rearranged and non-rearranged carbocation!
Watch Out!
Don't try and draw too many rearrangements! You will only have one 1,2-hydride shift or 1,2-methyl shift in any given reaction! This can save you from drawing too much side pathways.
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Example: Carbocation Rearrangements
Predict the product(s) of the following acid-catalyzed hydration reaction.
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Example: Carbocation Rearrangements
Predict the product(s) of the following acid-catalyzed hydration reaction.
