Under standard bimolecular elimination (E2) conditions, utilizing certain exceptionally bulky bases can actively completely reverse the typical regioselectivity, heavily favoring the less substituted

Question

Under standard bimolecular elimination (E2) conditions, utilizing certain exceptionally bulky bases can actively completely reverse the typical regioselectivity, heavily favoring the less substituted Hofmann product entirely over the highly substituted Saytzeff product. Which of the following bases are sterically massive enough to effectively enforce this specific Hofmann dominance?

Prashant Kotian · Accepted Answer

Correct answer: A,C. The final regioselectivity of E2 eliminations is fundamentally dictated by the physical steric bulk of the attacking base. Small, unhindered bases like ethoxide, methoxide, and plain amide efficiently tunnel in to access internal, heavily shielded -hydrogens to form the thermodynamically stable Saytzeff product. However, sterically massive, heavily branched bases like potassium *tert*-butoxide and lithium diisopropylamide (LDA) violently physically collide with the surrounding alkyl chain. To minimize this severe steric repulsion, they are forcefully restricted to attacking only the most exposed, terminal, primary -hydrogens, resulting in the overwhelming, almost exclusive formation of the less substituted Hofmann alkene.

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