Vibrational spectra and conformational isomerism of 2-phenoxy-5,6-benz-1,3,2-dioxaphosphepins

Using vibrational spectroscopy methods in different aggregate states and solutions with variation of the polarity of the medium, we have studied 2-phenoxy-5,6-benz-1,3,2-dioxaphosphepin and its oxo, thio, and seleno analogs. In the liquid and solutions, they exist as a conformational equilibrium of three forms: two chair forms, differing in the orientation of the phenoxyl radical, and a twist form. The population of the twist form is no more than 25%. The content of the chair conformers is determined by the solvent. In the crystal, all the compounds have the chair form with axial phenoxyl group. © 1989 Plenum Publishing Corporation

Ability of As=S group to form the hydrogen bond

The As=S group is capable of forming a hydrogen bond with phenol by functioning as the proton acceptor, in which connection the proton-acceptor capacity depends on the environment of the arsenic atom. The stability of the formed hydrogen bonds is somewhat higher than for the P=S group, but it is considerably lower than for the As=O group. © 1974 Consultants Bureau

Vibrational, NMR, photoelectron spectra and conformational analysis of seven-membered heterocycles

The article covered are the general principles of conformational analysis of 7-membered 1,3-dihetero-2-phosphepines and -silepines with one planar unit by means of spectral methods. The quantitative description of all possible conformers is given. Spectral criteria (the most informative bands in vibrational spectra, the shift difference and vicinal couplings in NMR spectra) for structural investigations are derived and on their basis the conformational condition is established depending on the nature of planar units and heteroatoms. © 1990

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

Spatial structure of phosphorus-containing heterocycles. 49. Vibrational spectra, dipole moments, and conformations of 2-aroxy-1,3,2-dioxaphosphepines and their benzo analogs

1. On the basis of IR and Raman vibrational spectra,1H NMR spectra, and measurements of dipole moments of 4,7-dihydro-2-aroxy-1,3,2-dioxaphosphepines, their 5,6-dichloro analogs are conformationally homogeneous and have a flexible T conformation with anti orientation of the phenoxyl radical. 5,6-Benzo-2-phenoxy-1,3,2-dioxaphosphepine is characterized by a three-component equilibrium in which both chair conformations and the twist conformation participate, with predominance of the first two. 2. In phenoxy-substituted 1,3,2-dioxaphosphepines, the plane of the benzene ring is nearly orthogonal to the plane of the {Mathematical expression}. © 1989 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

New data on the raman spectra of 1,3-bioxepane. Observation of a three-component equilibrium

A conformational equilibrium between three forms was detected in 1,3-dioxepane by Raman spectroscopy of the crystal, the liquid, and solutions with various polarities. The fraction of the predominant TC1 form in benzene solution is 0.9. © 1988 Plenum Publishing Corporation

Raman spectra and conformations of 2,2-dialkyl-1,3-dithio-5,6-benzocycloheptenes: coexistence of chair, boat and twist-boat forms

Raman spectroscopy has been applied to the title compounds; dithiaketals of acetone, methyl-ethylketone, ethylketone, pinacolone, cyclohexanone and fluorenone. A three-component chair⇋boat⇋twist-boat boat conformational equilibrium has been established for all compounds studied except the pinacolone derivative, which exhibits a two-component chair⇋boat equilibrium. Questions concerning the symmetry of the conformations based on depolarization data are discussed. © 1992

Vibrational spectra and structure of antimony (III) trialkoxides

1. According to their vibrational spectra, antimony trialkoxides of formula Sb(OR)3 with R=CH3, C2H5, n-C3H7, and i-C4H9 are associated; no signs of association are observed for the compounds with R=i-C3H7 and t-C4H9. 2. The molecules of antimony tri-t-butoxide in the liquid state at 20°C exist in the form of rotational isomers having C1 (Cs) and C3 (C3v) symmetry, with the C1 (Cs) conformer predominating. Upon freezing, the C3 (C3v) conformer remains in the crystal. © 1981 Plenum Publishing Corporation