Substituent and solvent effects on the N-2-N-3 hindered rotation of cis-1,3-diphenyltriazenes

Laser-flash photolysis techniques were applied to investigate the dependence of the rotational barrier about the N-2 - N-3 bond of symmetrically 4,4'-disubstituted cis-1,3-diphenyltriazenes on substituents and solvents. The increase in the rotational barrier with increasing ability of the 4-substituent to withdraw electrons implies the intramolecular process to be more susceptible to the electronic character of the aryl group attached to N-1 than of that bonded to N-3. Furthermore, the increase in the rotational barrier with decreasing solvent polarity implies an increase in dipole moment on rotation from the ground state to the transition state. Copyright (C) 2004 John Wiley Sons, Ltd.