Conformational analysis via LIF spectroscopy of jet-cooled molecules: hydroxy- and amino-benzoic acid esters

A vibrational spectroscopic investigation on benzocaine molecule

“…1b-d, the only difference between the two gauche conformers (G1 and G2), results from the different positions of the amino groups; the hydrogen atoms in the amino group in conformer G1 locate under the phenyl ring plain so as to be in the opposite side to the methyl group, whereas in conformer G2, the two hydrogen atoms locate over the phenyl ring plain and in the same side as the methyl group. The dihedral angles obtained for the gauche conformers G1 and G2 from the geometry optimizations carried out at B3LYP/6-31G(d), B3LYP/6-31++G(d,p), B3LYP/aug-cc-pvTZ and MP2/ 6-31++G(d,p) levels of theory, have clearly demonstrated that in both conformers, the plain of the amino group is not coplanar with the phenyl ring; which means that at room temperature both gauche conformers in theory should exist in the sample under spectroscopic investigation and accordingly contribute to the resultant experimental spectra of the free molecule, although only one possible gauche conformer for the molecule has been reported by McCombie et al [20] as well as Longarte et al [26]. According to the SCF energies obtained from both B3LYP and MP2 calculations, the trans T1 is the most stable one among the three stable conformers of free benzocaine.…”

“…In a conformational study carried out by Fernandez et al [17], water complexes of benzocaine were investigated with a combined approach of laser spectroscopic techniques and ab initio calculations performed using B3LYP method [18,19] with 6-31+G(d) basis set. Another conformational study based on the determination of the possible stable conformers of ethyl 4-aminobenzoate (benzocaine), methyl 4-aminobenzoate, ethyl www.elsevier.com/locate/vibspec 3-aminobenzoate and methyl 3-aminobenzoate molecules, was carried out by McCombie et al [20] by means of the experimental LIF spectroscopy and molecular modeling performed at semi-empirical MNDO and molecular mechanics MM2 levels of theory. To our best knowledge, the first theoretical vibrational spectroscopic studies on interpretation of the experimental IR and Raman spectral data of free benzocaine were carried out by Palafox in the light of the theoretical calculations performed at semi-empirical CNDO/2 level of theory [21,22].…”

Discrimination of Rotamers of Aryl Alcohol Homologues by Infrared−Ultraviolet Double-Resonance Spectroscopy in a Supersonic Jet

“…NMR 6,7 and electron diffraction 5 studies for benzyl alcohol supported the high abundance of the hydrogen-bonded form compared to the free form. Spectroscopic techniques involving high-resolution IR, microwave, laser-induced fluorescence, , multiphoton ionization, and rotationally resolved fluorescence excitation spectroscopies are also very much useful to throw light into the conformational complexity of flexible molecules in the ground and excited states.…”

Analytical Aspects of Amino, Quaternary Ammonium, Nitro, Nitroso and Related Functional Groups

“…Differences in band contour were ascribed to changes in hybridization caused by the conformational structure 356 .…”