M. Trachtman

An alternative approach to the problem of assessing destabilization energies (strain energies) in cyclic hydrocarbons

Abstract Reaction involving no hypothetical structures having averaged group energies or particular bond energy assignments are described, that provide an alternative basis for evaluating strain energies of cyclic hydrocarbons. These reactions match Cue5f8C bonds in the sense of having equal number of sp3-sp3, sp3-sp2, sp2-sp2, etc. bonds in reactants and products, while simultaneously matching various Cue5f8H bonds as closely as possible. Such reactions single out those structural features that lead to destabilizations of strained ring systems. Theoretical and experimental molecular indices are introduced as a measure of these destabilizing effects, and are compared ring strain energies.

The use of 90°-1,3-butadiene as a reference structure for the evaluation of stabilization energies for benzene and other conjugated cyclic hydrocarbons

Abstract Reactions are described that employ 90°-1,3-butadiene as a reference structure for the evaluation of the stabilization energyof the benzenoid and other cyclic conjugated hydrocarbons. The unique benefits of this rotamer of butadiene as a reference molecule within the homodesmotic conceptual framework are discussed. Experimental stabilization energies are presented for a number of cyclic hydrocarbons.

An ab innitio study of the structure, in-plane harmonic force field, and fundamental vibration frequencies of cis- and trans-acrolein

Abstract The structure, in-plane force field, and fundamental vibration frequencies of trans- and cis-acrolein are computed ab initio using 4-31G and (7,3) basis sets. Using a scaling procedure and spectroscopic masses, the vibration frequencies are calculated from ab initio force constant matrices, and found on average to be within 2.5% of the experimental values in the case of the trans conformer. The values predicted for the cis conformer, for which only a few tentative assignments have been made for spectroscopic observations, should facilitate the complete assignment in the future. Further experimental studies are necessary to resolve the substantial disagreement found between theory and experiment with respect to the length of the central formal carbon-carbon single bond in the series of molecules trans-glyoxal, trans-acrolein, and trans-1,3-butadiene.

An ab initio investigation of the harmonic force fields and vibrational frequencies of ethylene and cis- and trans-1,2-difluoroethylene

The harmonic force fields of cis- and trans-1,2-difluoroethylene, along with ethylene it-self, are computed ab initio in a (7,3) basis set contracted to 〈5,3〉. Both the force constants and derived frequencies are compared to the experimental values. In the case of the trans isomer the near degeneracy between the lowest frequency in-plane and out-of-plane fundamentals predicted by Craig and Overend is confirmed.

A theoretical study of the structure and spectrum of 1,3,5-hexatriene, Part II

Abstract The results of ab initio STO-3G and STO-4G calculations are reported on t Tt- and tCt -1,3,5-hexatriene, including a STO-3G partial geometry optimization of all C/C bond lengths in both isomers. Results are also reported from a partial INDO geometry optimization on.the t Tt-isomer, and complete optimizations on both isomers using empirical consistent force Meld programs. Significant discrepancies are found to exist between these calculated structures and those based on the electron diffraction analysis of Traetteberg. In addition, further results of a CNDO/S spectral analysis are presented and compared with experiment.

A theoretical study of the structure and spectrum of 1,3,5-hexatriene

Abstract Ab initio STO-3G calculations are performed on tTt- and tCt-1,3,5-hexatriene, including a partial geometry optimization on the tTt-isomer. These results are compared with the conclusions of Traetteberg based on an analysis of electron diffraction data. Some significant discrepancies are found, particularly with respect to the relative lengths of the central and terminal double bonds. In addition, a CNDO/S spectral analysis is performed at several different geometries and is compared with experiment.