Mechanism of reaction of tertiary methyl chloride with #"LiAlH"_4#?

1 Answer
Ernest Z.
Apr 27, 2018

Steric hindrance prevents attack by the #"AlH"_4^"-"# ion.

Explanation:

I believe you are asking about the reaction of #"LiAlH"_4# with tertiary alkyl chlorides.

#"LiAlH"_4# is a powerful hydride donor.

It reduces alkyl halides to alkanes.

#"R-Cl"color(white)(l) stackrelcolor(blue)("LiAlH"_4 color(white)(mm))(→) "R-H"#

The reaction works with primary and secondary alkyl halides, but not with tertiary halides.

Reaction

That's because the reaction is like an #"S"_text(N)2# displacement of a halide ion,

Here is a space-filling model of tert-butyl chloride as an attacking #"AlH"_4# ion might see it.

tBuCl

A bit of the chlorine atom is visible, but there is no room between the three methyl groups for the hydride ion to get at the carbon bearing the #"Cl"# atom.

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