base strength and steric bulk

When you choose a base for an elimination, two separate properties matter and they are easy to confuse. One is strength: how badly the base wants a proton (its conjugate acid's pKa). The other is bulk: how physically large and hindered the base is. A base can be strong and small, strong and bulky, or weak — and each combination steers the four-way competition differently.

Strength decides whether elimination goes E2 or leans E1. A strong base (hydroxide, alkoxide, amide) grabs the beta proton directly in a concerted E2; you need a high concentration of a reactive base to make the bimolecular step go. A weak base, by contrast, cannot drive E2, so elimination only happens by the slow E1 route after the leaving group departs on its own. Bulk, meanwhile, decides regiochemistry and the elimination-versus-substitution split: a small base can both attack the carbon (SN2) and grab a proton (E2), but a bulky base is too fat to reach the carbon, so it is shunted toward removing a proton — and toward the most exposed proton, giving the Hofmann (less substituted) alkene.

This is why specific bases are reagents of choice. Hydroxide and ethoxide are strong and fairly small: good for Zaitsev-type E2 but still capable of substitution. Potassium tert-butoxide is strong and very bulky: it forces E2 over SN2 and tends to give the Hofmann product. LDA (lithium diisopropylamide) is extremely strong and bulky. Picking the base is one of the main levers a chemist pulls to get the elimination — and the regiochemistry — they want.