Home > Organic Chemistry > Comparing and Determing SN1 or SN2 and E1 or E2 reactions

If the substrate is tertiary, can we rule out SN2?

Answer 1

Isaac Aronson

Yes, if the substrate is tertiary, can we rule out an #"S"_"N"2# mechanism.

An #"S"_"N"2# mechanism involves backside attack on the α carbon atom.

The three H atoms on a methyl carbon are tiny, so the nucleophile has a clear path for backside attack.

In a 3° substrate like t-butyl chloride, however, the bulky methyl groups block backside attack on the tertiary carbon.

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Answer 2

Elias Aguila

Yes, if the substrate is tertiary, SN2 reactions are highly improbable due to steric hindrance. Tertiary substrates favor SN1 reactions or other mechanisms over SN2.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.