A priori constraints in the force field calculations of polyatomic molecules

An inverse problem on calculating the force field parameters of a molecule from experimental data and its solution using regularizing algorithms are considered The choice of a priori constraints that may be imposed on solutions of the inverse vibrational problem is analyzed in terms of quantum mechanical calculations of some polyatomic molecules at different levels of theory, including electron correlation. Translated from Zhumal Struktumoi Khimii, Vol. 38, No. 2, pp. 221–239, March–April, 1997. Original article submitted June 14, 1996.     

Synthesis and Spatial Structure of the Derivatives of 2,5-Dioxo-3,3-Bis(Trifluoromethyl)-6,7-Benzo-1,4,2-and 2,5-Dioxo-4,4-Bis(Trifluoromethyl)-6,7-Benzo-1,3,2-Oxazaphosphepines

Abstract

Hexafluoroacetone imine easily interacts with compounds (I, R = OMe, OCH₂CF₂CHF₂, NEt₂, Ph) in two directions unlike hexafluoroacttone and gives 1,4,2-oxazaphosphepines (II) (pathway I) or 1,3,2-oxszaphosphepines (III) (pathway 2). The compound (II) (R = NEt₂) lightly hydrolyzes to yield the salt (IV). The structure of heterocycles II-IV) has been confirmed by X-ray analysis (see fig. I, II, R = OMe; fig. 2, IV). The detail structural peculiarities of the compounds am discussed.     

Conformational analysis of 5-substituted 1,3-dioxanes

Quantum-chemical study on the potential energy surface of 5-alkyl- and 5-phenyl-1,3-dioxanes at the RHF/6-31G(d) level of theory revealed two pathways for conformational isomerizations of the equatorial and axial chair conformers. Potential barriers to this process were estimated. The Gibbs conformational energies ΔG° of substituents at C⁵ in the 1,3-dioxane ring were determined on the basis of experimental (¹H NMR) and theoretical vicinal coupling constants, which turned out to be consistent with published data.     

Vibrational spectra and stable conformations of N-methylacetamide and (1S,5S,6R)-6-acetylamino-(5′-methoxyindolo[2,3-b])bicyclo[3.2.1]oct-2-ene

IR absorption and Raman spectra of N-methylacetamide and (1S,5S,6R)-6-acetylamino-(5′-methoxyindolo[2,3-b])bicyclo[3.2.1]oct-2-ene are investigated. Optimized structures and harmonic force fields of stable conformers of both compounds are obtained by means of MP2 and DFT (B3LYP) methods using the 6-31+G** basis set. Based on quantum mechanical calculations, a detailed interpretation of spectra is proposed and vibrational frequencies of the most stable conformations are assigned. Correlations between structures and the spectra of N-methylacetamide and (1S,5S,6R)-6-acetylamino-(5′-methoxyindolo[2,3-b])bicyclo[3.2.1]oct-2-ene were considered and analytical spectral regions were proposed.     

Molecular dynamics. Vibrational and35Cl NQR spectra of a 1,1,1,3,3-pentafluoro-3-chloropropane crystal

Journal of Applied Spectroscopy -     

Raman Structural Study of Copolymers of Propylene with Ethylene and High Olefins

Nascent form of random copolymers of propylene with ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene was studied by Raman spectroscopy. The most significant spectral alterations with a change in propylene content were observed in two lines at 809 and 841 cm⁻¹. The first line corresponds to vibrations of polypropylene helical chains in the crystalline phase, while the second one is associated with vibrations of polypropylene helical chains having isomeric defects. Raman data confirm that conformational composition and phase state of copolymer macromolecules strongly depend on the comonomer content as well as on the size of the comonomer units.     

Optically Active S‐Esters of Dithiophosphoric Acid on the Basis of (1S)‐endo‐(–)‐Borneol

The ammonium salt of optically active dithiophosphoric acid obtained by the reaction of tetraphosphorus decasulfide with (1S)‐endo‐(–)‐borneol reacts with benzoyl chloride, methyl chloroacetate and epichlorohydrin to form novel dithiophosphate S‐esters.