THE INFRARED SPECTRA AND THE STRUCTURE OF SOME HOMOPHTHALIMIDES

Abstract

“The number of tautomeric forms which homophthalimides, $C_{6}H_{4}CR^{\prime}^{\prime}R^{\prime}CONRCO$, can assume has continually raised the question of the structure of these compounds. Past studies of the chemical behavior and the ultraviolet and infrared spectra of these compounds, although enlightening, have not been without ambiguity in the assignment of a keto or enol configuration. In the 3 $\mu$ region the R $=$ H homophthalimides in the solid phase exhibit two absorptions at about 3.15 and 3.25 $\mu$, arising from associated NH stretching vibrations. In solutions of decreasing concentration, these two bands disappear and are replaced by one hand at 2.96 $\mu$. In the 6 $\mu$ region, the dilute solution spectra show two strong absorptions at about 5.82 and 5.87 $\mu$, arising from unassociated C $=$ O stretching vibrations. One of these vibrations is apparently perturbed in the solid phase, in which the absorptions occur at about 5.87 and 5.96 $\mu$. The $R = CH_{3}$ homophthalimides show no absorptions in the 3 $\mu$ region (other than CH stretching modes), and the two strong absorptions at about 5.84 and 5.97 $\mu$ are unchanged in both the solid and solution phase spectra. The spectra, including the concentration dependent band shifts and intensity changes of this group of homophthalimides are discussed with respect to the type of hydrogen bonding which occurs and to the assignment of a di-keto configuration for the homophthalimides.”