Generalized valence bond study of rotational singlet structures and pi bond energies for systems containing C=C, Si=Si, and C=Si double bonds

Article Abstract:

Generalized valence bond calculations of singlet state rotations around double bonds based on ab initio molecular orbital theory can determine pi bond energies and fluorine substitution effects in double-bond systems. The pi bond energy of the carbon-carbon bond in ethene is 65.4 kcal/mol, and decreases with fluorine substitution. The silicon-silicon bond in disilene has a pi energy of 23.2 kcal/mol, and the carbon-silicon bond in silaethene a pi energy of 31.6 kcal/mol.

Silicon, Olefins, Alkenes, Valence, Valence (Chemistry)

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Chiral N-(o-aryl)-thiazolidinediones: synthesis from rhodanines and investigation on rotational enantiomers by NMR spectroscopy

Article Abstract:

N-(o-aryl)-rhodanines which are sterically hindered (that is, N-(o-aryl)-2-thioxo-4-thiazolidinones) were synthesized. The N-(o-tolyl) and N-(o-chlorophenyl) derivatives were converted to their dioxo analogs (N-(o-aryl)-2,4-thiazolidine-diones). The compounds were shown through use of 1H and 13C NMR spectroscopy to be chiral in their conformational ground states through detection of the methyl groups or diastereotopic protons at C-5 of the heteroring.

Usage, Nuclear magnetic resonance spectroscopy, Chirality, Molecular structure, Molecular rotation, Rotation groups

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Ab initio conformational analysis of the model tripeptide N-formyl-L-alanyl-L-alanine amide

Article Abstract:

The model tripeptide N-formyl-L-alanyl-L-alanine amide (ALA-ALA) has been studied and two previously unreported energy minima have been described. The ab initio conformational energy minima were found by using ab initio RHF/6-31F gradient geometry refinement. The torsion angles of the ab initio energy minima are not what is found in typical substructures of proteins. Limitations of the dipeptide approximation have been examined.

Chemical structure, Alanine, Amides

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