Here’s a explanation of how substrate structure affects E1 and E2 reactions:
E1 Reactions
- E1 forms a carbocation intermediate, so carbocation stability is key.
- Tertiary substrates → react fastest (most stable carbocation).
- Secondary substrates → react moderately.
- Primary substrates → rarely react (unstable carbocation).
- Resonance-stabilized carbons (like allylic or benzylic) → react more easily.
E2 Reactions
- E2 occurs in one step, so carbocation stability is less important.
- Tertiary and secondary substrates → react well.
- Primary substrates → need a strong or bulky base.
- Steric hindrance affects which β-hydrogen the base can remove, influencing the major alkene (Zaitsev vs. Hofmann).
Key idea:
- E1 → favors stable carbocations (tertiary, resonance-stabilized).
- E2 → depends on base strength and accessibility of β-hydrogens, not carbocation stability.