EXPERIMENTAL AND THEORETICAL-STUDIES OF SUBSTITUENT EFFECTS IN HYDROGEN-BOND BASED MOLECULAR RECOGNITION OF A ZWITTERION BY SUBSTITUTED ARYLUREAS

Electron withdrawing groups have a strong effect on hydrogen bonding to aryl ureas. The effect of para substituents modestly exceeds the effect of meta substituents. Among common substituent parameters, sigma(-)(rho = 1.77, r(2) = 0.988) is found to be the best predictor for the observed effects of para substituents in aryl ureas. Semi-empirical and ab initio methods are used to calculate charge distributions in substituted benzene derivatives and in these ureas. A comparison of experimental and predicted (AM1, STO3G, 321-G*, 631-G**) dipole moments of benzene derivatives is presented. It is shown that calculated surface electric potentials for these thioureas successfully predict the relative hydrogen bonded association energies.