tert-Butyl chloride on treatment with LiAlH_4 gives 2-methylpropene but with NaBH_4 it gives 2-methylpropane . Why so ? Explain.

tert-Butyl chloride on treatment with LiAlH_4 gives 2-methylpropene bu

1.	tert-Butyl chloride on treatment with LiAlH_4 gives 2-methylpropene but with NaBH_4 it gives 2-methylpropane . Why so ? Explain.
Answer» Solution :Al-H bond is more polar (EN DIFFERENCE =2.1-1.5=0.6) than almost non-polar B-H bond (EN difference =2.1-2.0=0.1) .As a result , due to weak Al-H bond, `[AlH_4]^-` breaks to give `H^-` ION which ACTS a strong BASE and hence brings about dehydrohalogenation of `3^@` alkyl halides to form alkenes In contrast, due to strong B-H bond, `[BH_4]^-` acts only as a nucleophile and brings about a SUBSTITUTION reaction.