Chloroazobenzenes: IR and UV characteristics.

As p art of a continuing study of the biochemical transform ation of anilide herbicides and chloroanilines to azobenzenes 11 2, it was necessary to syn­ thesize a num ber of chloroazobenzenes 3’ 4 as analy­ tical standards and for use in tests of biological ac­ tivity. The UV and IR spectra of 13 chloroazobenzenes were determ ined to facilitate their identification. Bathochromic UV m axim a proved useful for the quantitative determ ination of chloroazobenzenes. At this wavelength, optical density was a linear function of concentration from 1 to 10 /^g/rnl methyl alco­ hol. The IR n = n stretching frequencies were related to chlorosubstitution of the azobenzenes. UV-Spectra: UV-spectra of ciV azobenzenes5-7 show weaker K-bands (bathochrom ic m axim a) than the spectra of the corresponding trans-isom ers. The additional shift of the K-bands to shorter wave lengths is the result of decreased resonance energy in the nonplanar molecules; the frarcs-azobenzene molecules have p lanar s tru c tu re s8. All the chloroazobenzenes listed in Table I showed K-band characteristics typical for frans-isom ers. The conclu­ sion, that all chloroazobenzenes were present in their trans-iorm was further supported by the fact that the K-band of 2, 3 and 4 were found to be in the