X-ray, DFT, FTIR and NMR structural study of 2,3-dihydro-2-(R-phenylacylidene)-1,3,3-trimethyl-1H-indole

Fischer base derivatives are widely used as precursor in the formation of different chemical switches. Besides, in the presence of acyl chlorides, indole enaminoketone derivatives can be prepared. 2,3-Dihydro-2-(R-phenylacylidene)-1,3,3-trimethyl-1H-indole, R = 4-NO2, 3,5-(NO2)2 and 4-OCH3, have been characterized previously but only by 1H NMR, thus further characterization was performed by FTIR, 13C NMR and when suitable crystals were obtained by single crystal X-ray diffraction analyses. The structures of the three molecules were additionally analyzed by DFT methods, B3LYP and PW91 functionals, using 6-311G(d,p) basis set. The optimized structures obtained were compared with those determined by crystallographic data. The probable assignments of the anharmonic experimental solid state vibrational frequencies for these molecules have been also made based on the calculated harmonic frequencies in vacuum at the same level of theory for the optimized structures. Correlations between experimental chemical shifts and GIAO calculated magnetic isotropic shielding constants with B3LYP and PW91 functionals using the 6-311++G(3df,3pd) basis set are also reported.