Theoretical calculations, kinetic stability

The successful synthesis and isolation of a series of heavy ketones (r r2M = X M = Si, Ge, Sn, Pb X = S, Se, Te) using kinetic stabilization (vide infra) and the remarkable progress in the field of theoretical calculations prompted chemists to perform computational calculations on the a and it bond energies as well as on the single and double bond lengths of H2M=X at the higher level of theory.14... 

In recent years, these donor-acceptor correlations to the reaction mode [49], substituent effects to stabilize meta intermediates [50-52], exo/endo selectivity [53-55], kinetics by means of fluorescence study [56] and deuterium isotope effect [57,58], formation and deactivation studies of exciplex [59,60], influence of pressure [61], and theoretical calculations [62-64] have been extensively studied. 

Numerous papers on CDs complexation of azo dyes concern stability, thermodynamics and kinetics of complexation and co-conformation The studies are followed frequently by theoretical calculations. 

At the same time, many theoretical calculations have been carried out over the last two decades to find new polynitrogens. Computational studies have been able to assist and encourage experimental work to find and identify unknown polynitrogens by providing information about molecular structures and kinetic stabilities on the potential energy surface with respect to N2. Many hypothetical structures of polynitrogens (from N4 to N60) have been predicted by quantum-mechanical calculations, which have led to the... 

The above ab initio and related calculations clearly reveal that unsaturated silicon compounds are less stable than their carbon analogs (156,170), but as gas-phase studies and the chemistry of sterically crowded silicon derivatives have proved (153,154,156,158,162,172-175) such compounds can no longer be labeled as nonexistent (176,177). A number of isolable double-bonded silicon derivatives have recently been synthesized and characterized in agreement with theoretical predictions (Table III) (169,173,178-195). The data illustrate well that the kinetic stability of multiply bonded silicon species can be greatly improved by substitution of sufficiently bulky groups across the p -pw bond. The ease of addition reactions is then severely restricted. The new target for organosilicon chemists appears to be silicon triple-bonded compounds (196,197). 

Theoretical calculations indicate a low stability for 21128 . The above reaction was examined by the technique of flash photolysis and kinetic mass spectrometry and a strong signal for the species C2H2S was observed, with a decay half-life of ca. 2 sec. Indirect, though compelling, evidence was presented to the effect that the signal was not due to a thioketene intermediate, CH2-C-S. Thiirene reacts rapidly with triple bonds to produce thiophenes, viz. 

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