Abinitio molecular orbital studies on thiirene and its isomeric structures

Abstract

This article is dedicated to Professor Harry E. Gunning on the occasion of' his 65111 birthclqRATNAKAR K. GOSAVI and OTTO P. STRAUSZ. Can. J. Chem. 61, 2596Chem. 61, (1983. Ab initio molecular orbital calculations have been carried out on the lowest closed shell singlet states of six isomeric forms of CzHIS at the SCF and C1 levels using STO-3G and 6-3 1G" basis sets. Molecular geometries of the isomers and the activatcd complexes for their isomerization reactions were optimized by the energy gradient method at the SCF .level and the C1 calculations were performed at these geometries. In addition, the lowest singlet and triplet states of the. SCHCH diradical were also studied and their geometries optimized by the Restricted Hartree Fock method.The computed stabilities follow the orderThe pseudo antiaromatic character of the 4n-T electron thiirene is manifested by its drastically reduced C-S bond energy, -15 kcal mol-I as compared to the value of >40 kcal mol-' estimated for its 21-1-71. electron analog, thiirane. This explains why thiirenes can be stabilized in inert matrices at 8 K but decompose readily at higher temperatures. In agreement with experimental results the lowest energy path for the unimolecular decomposition of thiirene leads to thioketene via the lowest singlet (or triplet) state of thioformylmethylene.The ir frequencies calculated for thiirene from rib initio mo theory using 6-31'3 + polarization functions on the sulfur show reasonably good agreement with the experimental frequencies, confirming the carlier assignments of the ir spectrum of thiirene. Les stabilites calculCes sont dans I'ordrc suivant:Le caractere pseudo antiaromatique de I'Clectron 41-1-71. du thiirene se manifestc par la reduction drastique de son Cnergie de liaison C-S de = 15 kcal mol-' telle que comparCe 6 la valeur supkrieure 6 40 kcal mol-' CvaluCe pour I'Clectron 211-71. analogue du thiirane. Ceci expIique pourquoi on peut stabiliser les thiirenes dans des matrices inertes 6 8 K mais ils se decomposent rapidement i des tempkratures plus 6levCes. En accord avec les rCsultats expCrimentaux, la voie de plus faible Cnergie pour la dCcomposition unimolCculaire du thiirkne conduit au thiocetkne via I'Ctat singulet (ou triplet) le plus bas du thioformylene.Les frkquences ir calculCes pour le thiirene 6 partir de la theoric ab irlitio des OM utilisant la base 6-31G + les fonctions de polarisation du soufre montrent un accord raisonnablement bon avec les frkqucnces experimentales confirmant ainsi les attributions anterieures du spectre ir du thiirene.[Traduit par le journal]

Resonance between the Ground Vibrational State and the Lowest Frequency Bending Mode of Thioketene

“…Ab initio molecular orbital calculations on thioketene have predicted optimized geometries at the 6-31G* A candidate for interstellar detection, thioketene (11) and SDCI/DZ / P (12) levels of theory, and more (H 2 C|C|S) has been extensively studied by microwave recently MP2/TZP geometries and vibrational frequencies (1 -3) and millimeter-wave spectroscopy (4). Although have been reported (13).…”

Mechanistic Investigations on the Photoisomerization Reactions of Five-Membered Ring Heterocyclic Molecules Containing Sulfur and Selenium Atoms

“…The photochemistry of 1,2,3-thiadiazole ( 1 ) has been the subject of many investigations over the past 50 years. − The experimental observations by Krantz, Laureni, and many chemists indicate that direct irradiation of 1 can produce thiirene ( 2 ), thioketene ( 3 ), and ethynethiol ( 4 ). − See Scheme . These experimental results strongly imply that the product distribution detected so far from direct photolysis is basically a characteristic of reactivity associated with the 1,3-diradical ( 5 ). − Its experimental detection, however, was anticipated could be very difficult because the early studies revealed that the energy of the intermediate ( 5 ) was computed to be much higher than those of the final photoproduct species ( 2 , 3 , and 4 ). , Moreover, these photoproducts were proposed to be yielded directly in the thiadiazole-excited state, in concert with nitrogen extrusion…”

“…23−42 Its experimental detection, however, was anticipated could be very difficult because the early studies revealed that the energy of the intermediate ( 5 ) was computed to be much higher than those of the final photoproduct species ( 2 , 3 , and 4 ). 43,44 Moreover, these photoproducts were proposed to be yielded directly in the thiadiazole-excited state, in concert with nitrogen extrusion. 45…”

“…23−42 Its experimental detection, however, was anticipated could be very difficult because the early studies revealed that the energy of the intermediate ( 5) was computed to be much higher than those of the final photoproduct species (2, 3, and 4). 43,44 Moreover, these photoproducts were proposed to be yielded directly in the thiadiazole-excited state, in concert with nitrogen extrusion. 45 It is well-known that selenium compounds show broad similarities with the corresponding sulfur analogues, that is, they offer utilizations in the syntheses of dyes, pharmaceuticals, and various fine chemicals.…”

Detection of keto-, thioxo- and iminocarbenes and the quintet state triplet-triplet ketocarbene radical pairs

“…In contrast to tetravalent carbon chemistry which ~s dominated by singlet ground states and phosphorescent excited triplet states, ground triplet states are of common occurrence in carbene chemistry, and keto-, thioxo-, and iminocarbenes are not expected to be an exception. In fact, ab initio molecular orbital calculations predict a ground triplet state for the parent formylmethylene [14], thioformylmethylene [15,16] and carboiminomethylene [17], Table I, and probably most of their derivatives also have a triplet ground state.…”