Bromination of alcohol

[Raiden2012]

So can someone please explain why we can substitute the alcohol group with bromine with HBr and not NaBr?

Thanks

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[Charles Darwin]

So can someone please explain why we can substitute the alcohol group with bromine with HBr and not NaBr?

Thanks

NaBr will form an alkoxide salt.

The H from the HBr will protonate the OH group, turning it into a good leaving group (water). The Br then attacks the carbocation, analogous to Sn1.

 

[vqtrinh]

-OH is a poor leaving group. The H+ from the HBr can protonate the -OH group of the alcohol. H2O is a better leaving group than the -OH. This allows Br- to act as a nucleophile in a substitution reaction.

 

[Singhp03]

-OH is a poor leaving group. The H+ from the HBr can protonate the -OH group of the alcohol. H2O is a better leaving group than the -OH. This allows Br- to act as a nucleophile in a substitution reaction.

👍bingo

 

[shaboobly]

oxygen has 2 lone pairs and one can readily accept a H+ to make water, which is a good leaving group. Br- then does its thing.