Alcohols donot react with NaBr but when H.SO, is added they form alkyl bromides. Explain.

Explanation

`ROH+Br^(-) to RBr +OH^(+)`
Although `Br^(-)` is a strong nucleophile, yet `OH^(-)` being a strong base is a very poor leaving group. Therefore, `Br^(-)` cannot displace `OH^(-)` from ROH to form RBr. Hence, alcohols donot react with NaBr.
However, when `H_(2)SO_(4)` is added, protonation of alcohola takes place and --OH group gets converted to `-OH_(2)^(-)` Since water is a weak base, therefore, it is a good leaving group. Hence, `Br^(-)` can displace `H_(2)O` from protonated alcohol to form RBr.
`R-OH+H^(+) hArr underset("Protonated alcohol") (R-overset(+)OH_(2))`