INFRARED-SPECTRA OF SUBSTITUTED POLYCYCLIC AROMATIC-HYDROCARBONS

Calculations are carried out using density functional theory (DFT) to determine the harmonic frequencies and intensities of 1-methylanthrace ne, 9-methylanthracene, 9-cyanoanthracene, 2-aminoanthrocene, acridine , and their positive ions. The theoretical data are compared with matr ix-isolation spectra for these species also reported in this work. The theoretical and experimental frequencies and relative intensities for the neutral species are in generally good agreement, whereas the posi tive ion spectra are only in qualitative agreement. Relative to anthra cene, we find that substitution of a. methyl or CN for a hydrogen does not significantly affect the spectrum other than to add the character istic methyl C-H and C drop N stretches near 2900 and 2200 cm(-1), res pectively. However, addition of NH2 dramatically affects the spectrum of the neutral. Not only are the NH2 modes themselves strong, but this electron-withdrawing group induces sufficient partial charge on the r ing to give the neutral molecule spectra characteristics of the anthra cene cation. The sum of the absolute intensities is about four times l arger for 2-aminoanthracene than those for 9-cyanoanthracene. Substitu ting nitrogen in the ring at the nine position (acridine) does not gre atly alter the spectrum compared with anthracene.