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Ab initio anharmonic force field and equilibrium structure of vinyl bromide

“…However, ab initio calculations at the coupled cluster level of theory with a basis set of quadruple zeta quality can give reliable results provided the calculated structure is corrected by an offset derived from structurally similar molecules whose equilibrium structure is already accurately known [12]. It has also been found that the correlation consistent triple zeta valence basis set with the Stuttgart-Dresden-Bonn relativistic effective core potential (SDB-cc-pVTZ) [13] employing the second-order Møller-Plesset perturbation theory (MP2) [14] gives reliable results, particularly for the force field.…”

When Is the Substitution Structure Not Reliable?

“…In order to get a reliable structure, it is important to check that the system of normal equations of the least squares fit is not ill-conditioned and to improve the conditioning, if necessary, using additional information (28). In this case, it has been shown that empirical correlations between geometrical parameters and other types of parameters can be extremely useful (24,29,30). These methods have been recently critically reviewed and applied to the determination of the structure of several molecules: 1,2,5-oxadiazole, c-C 2 H 2 N 2 O (31), cis-thionylimide, HNSO (32), methyl isocyanide, CH 3 NC (33), and 1,2-dicyanocyclobutene, C 4 H 4 (CN) 2 (14).…”

“…They are particularly well adapted to confirm our assumption because they are simple as far as the structure is concerned and they will enable us to point out a pattern. The first example is the structure of halo-cyanoacetylenes, X-C≡C-C≡N (X = H, F, Cl, Br, I) which has been recently redetermined (24). The results have been collected in Table 3.…”

“…Most of them have been independently determined several times. Particularly, the structure of halo-cyanoacetylenes in Table 3 has been checked using different empirical correlations (24).…”

Interplay of Thermochemistry and Structural Chemistry, the Journal (Volume 14, 2003) and the Discipline

“…In the next issue, Demaison et al discuss carbon halogen bonds in halo and dihaloacetylenes [33]. The experimental thermochemistry of all of these species is unreliable, as clarified by considering high-level post Hartree-Fock mathematical theory that has been useful for understanding the energetics of the fluoro and chloro compounds [34].…”