1,2 Hydrogen shifts in thioformaldehyde (H2CS), phosphazene (HNPH) and diphosphene (HPPH): In-plane versus out-of-plane migration

Comparative ab Initio Study of Molecular Structures and Relative Stabilities of Germanone, Germathione, Germaselenone, and Their Structural Isomers

“…Together with the minimum-energy structures shown in Figure , we have located also the transition states for trans -HGe−SeH ↔ cis -HGe−SeH and H 2 GeSe ↔ trans -HGe−SeH isomerization reactions (Figure ). It is interesting that H 2 GeSe ↔ trans -HGe−SeH isomerization proceeds via two, planar and nonplanar, transition structures that have been also found in the study of H 2 CS ↔ trans -HC−SH and H 2 NN ↔ trans -HN−NH isomerizations but not for, for example, the H 2 CO ↔ trans -HC−OH reaction. The revealed transition states are also structurally similar to those found previously 11,13 for trans -HGe−OH ↔ cis -HGe−OH, H 2 GeO ↔ trans -HGe−OH, trans -HGe−SH ↔ cis -HGe−SH, and H 2 GeS ↔ trans -HGe−SH isomerization reactions.…”

Reaction path as a gradient line on a potential energy surface

“…The situations with two equivalent TS and RTS are encountered rather frequently in practical ab initio calculations [63-701. For example, the ab initio calculations [63] that include the correlation energy of molecules H2PN and H2PP clearly indicate the existence of two equivalent TSs on two nonprincipal GLs entering the minimum tangentially to the +ql (the same is valid for the two -q1 GLS) in the 1,2-H-shift reaction 8 2 11. The reaction path consisting of two GLS starts either along +q1 or -q1 (out-of-plane mode corresponding to the smallest Hessian eigenvalue), simultaneously proceeds via two TSS, 9a and 9c (or 9b and 9d), and enters minima l l a and l l b .…”

“…The schematic map of the H2PN PES are presented in Figure 7. In such a case, it is easy to show by using Morse theory [71] that a critical point (planar structure 10 [63]) with A = 2 must lie on the q2 principal GL.…”

B3LYP and CCSD(T) Studies of the Mechanisms of Unimolecular Reactions of HXCS (X = H and F)

“…Some of the compounds with a carbon−sulfur double bond, a so-called thiocarbonyl group, have been noted as building blocks in organic synthesis and as important intermediates in the synthesis of sulfur-containing molecules. − In fact, the chemistry of thioformyl compounds has been studied extensively in recent years, not only because of their unique structures but also because of their potential biological activities. , However, the role of sulfur in biological structures largely remains unknown. Some knowledge of its function in biomolecules may perhaps be gained by the study of small model systems. , Thus, thioformaldehyde (H 2 CS), the smallest thioketone, should be related to systems of biological importance. − ,− Nevertheless, the synthesis and isolation of thiocarbonyl compounds have in general proved very difficult to study by standard techniques because of their instability . It is therefore not surprising that the first kinetically stabilized thioaldehyde, which is stable at ambient temperature, was made only recently. ,, …”