Question

neopentyl bromide undergoes nucleophilic substitution reaction very slowly

Answer 1

Since, Bromine is attached to a carbon, where the neighboring carbon group has large number of alkyl substituents, it experiences steric hindrance( like a shielding effect to prevent nucleophillic attack). This is the reason why this nucleophillic substitution is very slow.

Answer 2

Explanation:

Neopentyl chloride undergoes substitution reactions slowly because of steric hindrance.

bulky methyl group make it difficult for the nucleophile to attack from back side of carbon atom C-Cl bond.

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