Description: Addition of aqueous acid to alkenes leads to the formation of alcohols.
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Oh wow, this is a major brain fart. Thanks Dave.
With problems where you’re given the reactant and the product and you’re to guess the reagent how do you know whether to choose aqueous acid or oxymercuration?
Oxymercuration is generally the best and safest choice. Aqueous acid leads to carbocation formation, and carbocations can rearrange under certain conditions.
Would there be products with stereochemistry in examples 3 and 4?
3 yes, because we make a new chiral centre. 4 no, because the carbon the OH is attached to is not a chiral centre.
With the example with the alkene with the pentane, how come the OH attached to the carbon that’s part of the pentane instead of the next carbon to the right that’s part of the side chain? Isn’t the OH suppose to attach to the more substituted carbon that’s part of the double bond??
Hi Casey! last example is a rearrangement. Forms a secondary carbocation initially and then there is a hydride shift which generates a (more stable) tertiary carbocation which is then trapped by water.
Got it. Thank you for the explanation!
James wouldn’t the last one remain where it is because the allylic is more stable than the tertiary?
Hi Marie, the last one (example 4) actually forms a secondary carbocation, not an allylic carbocation.
Why doesn’t ring expansion happen in example 4
In general, hydride migrations are faster than carbon migrations. Smaller atom, less reorganization.
Hey James, Does the oxygen in step 3 of the mechanism have a positive charge?
Yes – fixed that. Thank you!
This is SN1 correct?
No, this is an addition reaction, not a substitution reaction.
For the last rearrangement with the shift, when does this shift take place? At what step of the mechanism?
The shift happens after carbocation formation, but before the attack of water on the carbocation. Another example: https://www.masterorganicchemistry.com/reaction-guide/additions-to-alkenes-accompanied-by-12-hydride-shifts/
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