Rotation around (Y)Csp2 X bonds (XC, O; YCsp2 , O) within the framework of the molecular mechanics method

Internal rotation around (Y)Csp2- X (X=;C, O; Y=;Csp2 , O) bonds is considered. A calculation scheme, taking into account heteroatom lone pair interactions, is used. Wide literature information, concerning the rotation discussed here, is gathered and analysed. Rotation barrier uniform values are proposed on the basis of original simulations and their nature is discussed. © 1990

Three-Dimensional Structure of P and B, N Or S-Containing Six-Membered Heterocycles

An analysis of conformational features of six-membered ring systems of the type of 1, 3, 5-diheterophosphorinanes with tri-and tetracoordinated phosphorus is given. Using IR, NMR spectra, dipole moments, as well as molecular mechanic calculation it was found the energy difference between chair and flexible shapes is not large enough, as in six-membered organic cycles, which causes participation of twist or boat in conformational equilibrium. © 1992, Taylor & Francis Group, LLC. All rights reserved

Conformational study of dibenzo[d,g][1,3]dioxocin-12-one by vibrational spectroscopy and molecular mechanics

Two of the four possible dibenzo [d,g][1,3]dioxocin-12-one conformers are identified in solution from IR and Raman spectra. The experimental enthalpy difference between boat-chair (BC) and twist T) conformers of 0.7 kcal mol- is obtained from temperature dependent IR spectra. Structural parameters and the potential energy difference (1.4 kcal mol-1) for these conformers are calculated by molecular mechanics. Band shape simulations and normal coordinate analysis are applied when they are necessary for interpretation of the experimental results. The conformational equilibria seems to be non-typical for cyclic systems with two planar units in 1,4 position. © 1991

Vibration spectra and conformations of 1,3,2-dioxaphosphorinanes containing an exocyclic P-N bond

1. Unsubstituted 2-dialkylamino-1,3,2-dioxaphosphorinanes with three- and four-coordinated phosphorus exist as a mixture of two conformers in the liquid and solutions of polar solvents according to the vibration spectral data and calculations by the method of atomic-atomic potential functions; the conformers with an equatorial orientation of the dialkylamino group is energetically more advantageous and is realized in a crystal. 2. The cis-isomer of 2-diethylamino-2-thio-4-methyl-1,3,2-dioxaphosphorinane is conformationally homogeneous. Conformational equilibrium in which three conformers participate based on the results of the calculations: two chair and boat forms, is found for the less stable trans-isomer. © 1985 Plenum Publishing Corporation

Vibrational spectra and conformations of 1,3,2-dioxaphosphepines with exocyclic P-N bond

1. The change in the vibrational (IR, Raman) spectra of nine 2N,N-dialkylamino-5,6-benzo(4,7-dihydro)-1,3,2-dioxaphosphepine during extensive variation of their temperature, aggregate state, and medium indicates the existence of a structure-dependent ability of the molecules to participate in different conformations. 2. Under the above-described experimental conditions, in 5,6-benzo-1,3,2-dioxaphosphepines with a tetracoordinated phosphorus atom and in the 4,7-dihydro derivatives studied, the conformational equilibrium is preferentially shifted in one direction. In the case of 5,6-benzo derivatives of trivalent phosphorus, in a liquid phase an equilibrium is observed of comparable amounts of the two forms of the molecules. 3. The quantitatively dominating, energetically more convenient, and the only remaining in the crystal form in the molecules of 5,6-benzo-1,3,2-phosphepines is the chair conformation with an equatorial P-N bond. © 1985 Plenum Publishing Corporation

Rotation around (Y)Csp2 X bonds (XC, O; YCsp2 , O) within the framework of the molecular mechanics method

Internal rotation around (Y)Csp2- X (X=;C, O; Y=;Csp2 , O) bonds is considered. A calculation scheme, taking into account heteroatom lone pair interactions, is used. Wide literature information, concerning the rotation discussed here, is gathered and analysed. Rotation barrier uniform values are proposed on the basis of original simulations and their nature is discussed. © 1990

Three-Dimensional Structure of P and B, N Or S-Containing Six-Membered Heterocycles

An analysis of conformational features of six-membered ring systems of the type of 1, 3, 5-diheterophosphorinanes with tri-and tetracoordinated phosphorus is given. Using IR, NMR spectra, dipole moments, as well as molecular mechanic calculation it was found the energy difference between chair and flexible shapes is not large enough, as in six-membered organic cycles, which causes participation of twist or boat in conformational equilibrium. © 1992, Taylor & Francis Group, LLC. All rights reserved

Three-Dimensional Structure of P and B, N Or S-Containing Six-Membered Heterocycles

An analysis of conformational features of six-membered ring systems of the type of 1, 3, 5-diheterophosphorinanes with tri-and tetracoordinated phosphorus is given. Using IR, NMR spectra, dipole moments, as well as molecular mechanic calculation it was found the energy difference between chair and flexible shapes is not large enough, as in six-membered organic cycles, which causes participation of twist or boat in conformational equilibrium. © 1992, Taylor & Francis Group, LLC. All rights reserved

Three-Dimensional Structure of P and B, N Or S-Containing Six-Membered Heterocycles

An analysis of conformational features of six-membered ring systems of the type of 1, 3, 5-diheterophosphorinanes with tri-and tetracoordinated phosphorus is given. Using IR, NMR spectra, dipole moments, as well as molecular mechanic calculation it was found the energy difference between chair and flexible shapes is not large enough, as in six-membered organic cycles, which causes participation of twist or boat in conformational equilibrium. © 1992, Taylor & Francis Group, LLC. All rights reserved