Vanillin reacts with p-anisidine in 1:1 molar ratio in the solid and molten states, in microwave oven and in solution. In all the cases, reaction occurred with the formation of N-(4-methoxy phenyl)-4-hydroxy-3-methoxy phenyl methanimine (NHM) and water. Single crystal X-ray analysis shows that NHM crystallizes in the chiral orthorhombic space group P2(1)2(1)2(1). An optimized geometry of NHM was computed by using density functional theory. In the case of solid-state reaction, it is proposed that a thin lawyer of water molecules is formed at the junction of vanillin and p-anisidine which moves progressively towards vanillin as the reaction proceeds. The overall mechanism of solid-state reaction. has been proposed by a model.