Structural studies on bio-active compounds. Part 18. Crystal structure and molecular modelling of methyl 4-(3-ethyl-3-hydroxymethyltriazen-1-yl) benzoate.

The title compound is an isomer, differing only by the shift of a methyl group, of the anti-cancer agent ethyl 4-(3-hydroxymethyl-3-methyltriazen-1-yl) benzoate; yet its half-life at physiological pH is only one-third as long. It forms crystals with triclinic symmetry, space group P1, and unit cell dimensions a = 6.184 (2), b = 7.214 (2), c = 14.575 (2) A, alpha = 89.61 (2), beta = 79.96 (2), gamma = 68.76 (2)0. Its labile N-CH2OH bond is slightly shorter than that of the more stable isomer but becomes almost equal after optimization of geometry by semi-empirical molecular orbital techniques. Calculated heats of formation are virtually identical for these compounds, as they are for the daughter species after loss of CH2O. The hydroxyl group forms an intermolecular hydrogen bond to a carboxyl oxygen atom in preference to the less negative triazene N(1).