OPTICALLY-ACTIVE AMINES .28. SPECTRAL OBSERVATIONS ON CHIRAL N-SUBSTITUTED PARA-NITROANILINES

Electronic absorption (EA) and circular dichroism (CD) measurements with a series of chiral N-substituted p-ni-troanilines in conjunction with CNDO/S calculations with p-nitroaniline show that the strong absorption band of p-nitroaniline in polar solvents at about 385 nm is long (z) axis polarized and that near 235 nm contains a strong short (x) axis and a weak z axis polarized transition. These are assigned as transitions to the 2A1, 3B1, and 3A1 and/or 4A1 excited states, respectively. The weak shoulders at about 315, 300, and 265 nm are identified as x axis polarized. The low-energy pair is assigned to totally symmetric vibrational modes of the 1B1 transition, and the other to the 2B1 transition. These assignments are, with minor exceptions, in general agreement with those made previously. © 1979, American Chemical Society. All rights reserved.