Ground electronic state of silylene

Abstract

coupling of electronic and nuclear motions, and other nuclear dynamic effects can be assumed to be negligible. It should be emphasized that the same fundamental basis governs the operation of both sets of symmetry rules and in this respect the two sets of rules are fundamentally similar.The examples, given in section IV, show that Wigner-Witmer and Woodward-Hoffmann rules give equivalent results to the extent that total orbital symmetry can be useful but that the Woodward-Hoffmann rules can often provide a further distinction between possible reaction paths by considering individual orbital symmetries as well. The examples include cases where total symmetry is sufficient to analyze a reaction and 5967 also cases where an examination of individual symmetries is required.The hierarchy of symmetry control rests on the occurrence of energy barriers of different heights being encountered, along various reaction coordinates, corresponding to the degree of concordance or discordance of symmetry species from reactant to product wave function structures.The possible experimental observation of "forbidden" processes23•29-33 presages the need to emphasize that these different barrier heights do not control the reaction destiny in an absolute sense but only affect the various probabilities of reaction along different paths. However, for many purposes,14 this degree of reaction control is quite important.

Chemical Kinetics and Hot Atom Chemistry — Present Status and Future Perspectives

“…A recent example from silicon chemistry indicates that product studies can be quite revealing mechanistically for polyvalent recoil atoms, particularly if some supplementary information is available from thermally induced reaction studies. Both the TANG and GASPAR groups have studied the reactions of recoiling silicon atoms with butadiene [196][197][198][199], 31 Si + Hi 31 Si 31 SiC 4 H 6 [197,199] Possible structures for 31 [196], an apparent product of silylene addition. The major product, however, was assigned an empirical formula 31 SiC 4 H 6 and the silacyclopentadiene structure was favored [197], although attempts to synthesize the authentic compound have thus far been unsuccessful.…”

Tetramethyl-1-silacycloprop-2-ene: its characterization and reactions

“…Scavenger . experiments done on reactions of recoiling silicon atoms have been interpreted as scavenging triplet Si H2 [28,29] 31 and Si F2 [32]. 31…”

Reactions of monomeric silicon difluoride and silylene with conjugated pentadienes

“…18 Later, we have shown in our laboratory that the 31SiH2 thus formed can add 0020-1669/78/1317-2802S01.00/0 © 1978 American Chemical Society to 1,3-butadiene to give silacyclopent-3-ene-nSi (SCP*) (eq I).22-23 Studies using nitric oxides as a scavenger demonstrate that the reacting silylene is present as 80% triplet and 20% singlet, while studies using neon as a moderator proved that the ground electronic state of silylene is a singlet. 25 The ground electronic state of SiF2 has been spectroscopically established by Margrave and co-workers as a singlet. 15 Chemically it is extraordinarily stable, having a half-life at 0.1 Torr of 150 s. They have demonstrated that when SiF2 is formed in high concentrations by the thermal vaporization method, the SiF2 species dimerize very readily upon condensation to give (SiF2)2 and undergo further interactions in this dimer form.4,5 With the nuclear recoil technique, we have formed 31SiF2 by irradiating PF3 with fast neutrons.…”