Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene are orthorhombic,a = 8.7283(6),b = 8.8369(5),c = 18.8798(8) Å,Z = 4, space groupP21ab. It is resolved toRF = 0.053 for 684 observed reflections. Crystals of 2-N-phenylamino-4-N-phenylimino-2-pentene hydrochloride are monoclinic,a = 14.6120(9),b = 5.2736(7),c = 20.708(1) Å, β = 102.287(5)°,Z = 4, space groupP21/c. The final residual is 0.054 for 1255 reflections. Crystals of 2-N-methylamino-4-N-methylimino-2-pentene hydrochloride are trigonal,a = 7.1666(7).c = 15.3299(8) Å,Z = 3, space groupP3121. The final residual is 0.044 for 343 observed reflections. The free base exists, in the solid, as the amino-imino form and not as a symmetrical structure. The N—H bond distances in the six-membered ring of the free base are equal as are the N—H bond distances in the infinite chains of the hydrochloride salts. The compounds are fluxional in solution.