E1 vs E2
MCAT glossary · MCAT
Definition
E1: unimolecular, carbocation, mixed regiochemistry, Zaitsev product; E2: bimolecular, anti-periplanar H/LG, Zaitsev (usually) with strong base.
E1 vs E2 in plain English
These are two ways a molecule sheds a small piece to form a double bond (an 'elimination' reaction). Think of a wall with a sticky note (a hydrogen, H) and a magnet (the leaving group, LG) attached nearby; pulling both off lets a new bond snap into place. In E2, a strong base yanks the H off at the exact same moment the LG leaves — one smooth, coordinated step ('bimolecular'), and it needs the H and LG lined up on opposite sides ('anti-periplanar'). In E1, the LG leaves first on its own, creating a temporary positive charge ('carbocation'), and only then does the H drop off — two steps, slower, and messier about where the double bond ends up. Both usually favor the 'Zaitsev' product, meaning the double bond lands in the more crowded, more stable spot.
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