Determination of the difference in the energies of the isomers of the molecules of oxalyl chloride and oxalyl fluoride

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part II: Theoretical investigation of oxalyl chloride

“…The VFPA conformer energy difference is in agreement with the latest electron diffraction [13] and spectroscopic data [18,23]. This fact is rather important to confirm the experimental model since many theoretical methods do not predict the existence of the second conformer.…”

“…[18] 289 (110) b --Exp. [23] 340 (100) --Exp. [13] c 351 d 391 815 B3LYP/6-311+G(d) [20] 7 -755 B3LYP/6-311+G(2d) [20] -14 -790 MP2/6-311+G(d) [20] 143 -843 MP2/6-311+G(2d) [20] 133 -773 MP2/6-311+G(3df,2p) [47] 176 215 -MP2/cc-pVQZ [22] 216 245 753 MP2/cc-pV5Z [22] 229 259 718 CCSD(T)/cc-pVQZ [22] 260 -816 G2 [ for the cis-conformer according to one-particle energies and/or natural MO occupations does not provide correct information on the order of the electronic states.…”

“…According to these studies, oxalyl chloride exists as trans-and gauche-conformers with the value of the dOCCO angle for the gauche conformer being 76(18)° [13]. The obtained values for the conformer energy or enthalpy differences are 395(65) [13], 289(110) [18], and 340(100) cm À1 [23] in the gas phase and 111 (49) cm À1 [18] in a liquid xenon solution. The geometric parameters of both conformers were determined in [13] for a model with fixed geometrical parameters except for the torsion angle.…”

Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part I: Reanalysis of the 3680Å and 4100Å absorption systems of oxalyl chloride

“…However, later electron diffraction [10] and vibrational spectra [5,22,27] (enthalpy) differences in the gas phase to be only 300 cm À1 , and consequently, the trans-and gauche-conformers were present in comparable amounts. Therefore, the absence of gauche-oxalyl chloride transitions in the vibronic spectra needs explanation.…”

“…However, no data on the structure of the second conformers of oxalyl halides in excited electronic states are available. Earlier, only transitions of the trans-conformers were observed in the vibronic absorption spectra of oxalyl halides [14,16,[18][19][20], although according to vibrational spectroscopy and electron diffraction studies, the values of conformer energy (enthalpy) differences of oxalyl halides in the ground electronic state in the gas phase were relatively small, and the content of the second conformers was rather high [2,[4][5][6][9][10][11]22].…”