Syntheses and properties are described for sterically shielded imines R2C = NR (3c, e, g–k), which are rather inert toward nucleophiles. Nucleophilic attack at the nitrogen atom of 3k is indicated by the formation of the azine 4. (E,Z) Configurational diastereotopomerization (anti/syn) is strongly dependent on N substituents [CH3, phenyl, 1-naphthyl, acetyl, Si(CH3)3, cyano, SC6H5, SOC6H5, SO2C6H5, and nitro]. It is accelerated by front strain along the CN bond in 3a–c, e, g, h, j, and k and provides an energetic basis (by ΔG≠ and ΔΔG≠ values) for the gauging of force-field parameters. This (E,Z) stereo-mutation is characterized by a vanishing solvent dependence and a positive volume of activation (+10.2 cm3 mol-1 for 3a). In contrast to other π acceptor substituents, the N-nitro group in 31 retards (E,Z) interconversion.