Flippin-Lodge angle

The Flippin-Lodge angle is the lateral angle of nucleophilic attack to a carbonyl or similar, i.e. in the same plane as the carbonyl and its substituents, when Bürgi-Dunitz angle is the angle in the perpendicular plane.

Stereoselectivity increases with a lower Flippin-Lodge angle, which is determined by the steric bulk of the substituents of the carbonyl. Thus, aldehydes have lowest selectivity, and tert-butyl ketones highest.