Phosphorus compounds with eight-membered heterocyclic systems: Synthesis and three-dimensional structure

An analysis of the conformational behaviors of phosphorus compounds with different types of eight-membered heterocyclic systems (saturated and unsaturated organic and inorganic systems, their metal complexes as well as metallocycle derivatives) is given. By using the quantitative criteria (torsional angles and puckering parameters) as a description of the conformational state, it is possible to provide a sufficiently complete and consistent picture of their three-dimensional structure in the solid and solution state. A conclusion about the electronic effects which govern their conformational behavior is made. Special attention is paid to the description of synthetic routes to eight-membered heterocycles and of spectroscopic indicators for the reliable identification of conformers. © 1992, Taylor & Francis Group, LLC. All rights reserved

Intramolecular Electronic Interactions in Phosphorus Compounds in the Light of Recent Structural Studies

The nature and mechanism of intramolecular electronic interactions in compounds of three- and four-coordinate phosphorus have been critically examined on the basis of a review of the results of the study of their three-dimensional structure and physical properties. The high π-acceptor power of phosphorus-containing groups, capable of stabilising conformations with the trans-orientation of the interacting orbitals of the donors (the n-orbitals of the unshared electron pairs of the heteroatoms or the π-orbitals of unsaturated systems) and the acceptors (bonds of the phosphorus atom) has been proved. The bibliography contains 193 references. © 1984 The British Library

Spatial structures of phosphorus-containing heterocycles - 12. Bond polarities and conformations of the 2-dialkylamino-2-oxo-1,3,2-dioxaphosphorinanes

1. A determination has been made of the dipole moments of the phosphoryl group in the axial and equatorial chair conformations of 2-dialkylamino-2-oxo-1,3,2 -dioxaphosphorinane. 2. The phosphoryl bond has predominantly axial orientation in 2-dialkylamino-2-oxo-1,3,2-dioxaphosphorinanes. 3. A determination has been made of the preferred conformations of axial and equatorial NMe2 groups. © 1977 Plenum Publishing Corporation

Contemporary ideas about the conformations of eight-membered cyclic systems with planar fragments

The results of conformational studies on eight-membered cyclic compounds that contain from one to four planar fragments in exo- or endo-cyclic positions of the molecule have been correlated. By analysing the systematic changes in the torsion angles and folding parameters, which were selected as the main quantitative criteria of the conformational state of the class of compounds being examined, it is possible to present a sufficiently complete and consistent picture of their conformational behaviour, which has a diversity that is determined by the relative configuration and nature of both the planar fragments and the heteroatoms contained in the ring. Special consideration has been given to the basis for the NMR spectroscopic criteria used in identification of the respective conformations. The bibliography includes 230 references. © 1988 IOP Publishing Ltd

Boat conformation in 2,5-substituted 1,3-dioxanes

The calculation of the energy equilibrium according to Pitzer between the chair and boat conformations in 2,5-substituted 1,3-dioxanes is presented, as well as the energies of the electrostatic dipole interactions. It is shown that the unsymmetrical boat conformation is stabilized in 2,5-dialkyl- and in 2,2-dimethyl-5-alkyl-5-α-alkoxyalkyl-1,3-dioxanes because of the presence of hetero atoms in the ring, because of the introduction of substituents in the 2 and 5 positions, and because of the interaction between the hybridized, unshared electron pairs of the oxygen atom at the apex of the boat with the hydrogen atom of the CH2 group. © 1970 The Faraday Press, Inc

Acceptor properties and conformation isomerism in CH2CH-PX2 (X = F or Cl) compounds

Ab initio calculations of CH2CH-PF2 and CH2CH-PCl2 were performed to investigate their conformational isomerism. It has been shown that both compounds have two conformers: the cis and the eclipsed. The concept of group orbital interactions was used to analyse the electronic structure and geometry of these molecules. The most stable conformer of CH2CH-PX2 has a cis orientation of the phosphorus lone pair and the CH2CH group due to the alkene-PX2 hyperconjugation. From PMO and Mulliken population analysis, the PX2 fragment acts as a π acceptor. © 1990

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

Spatial structure of phosphorus-containing heterocycles - Communication 28. Conformation of phenyl radical in 5-phenyl-5-oxo-1,3,5-dioxaphosphorinanes and thiono analogs

1. On the basis of data on the Kerr effect in solutions, the stereoisomers of 5-phenyl-5-oxo- and 5-phenyl-5-thiono-2,4,6-trimethyl-1,3,5-dioxaphosphorinanes, differing in the position of the exocyclic substituents on the P atom, are characterized by nearly parallel orientation of the plane of the benzene ring and the plane of the bonds {Mathematical expression}. In the conformation that we have found, optimal structural conditions are realized for resonance interaction of the π-orbitals of the phenyl radical and the P=X bond. 2. This sort of interaction in the UV spectra is manifested in a bathochromic shift of the benzene absorption bands (particularly λ2) and their intensification. In the sulfides, the absorption bands of the benzene overlap those of the thiophosphoryl group. © 1982 Plenum Publishing Corporation

Possible causes of the stabilization of the axial S=O bond in cyclic sulfites and sulfoxides

1. The possible causes of stabilization of the axial S=O bond for six-membered cyclic sulfites and sulfoxides were discussed. In the case of sulfites, the basic role may be played by interaction between the unshared electron pairs of the endocyclic oxygen atoms and the free d-orbitals of the sulfur atom and dipole-dipole interaction. The influence of the Van der Waals attraction of the atoms and steric requirements of the unshared pair of electrons is negligible. 2. The energy difference between the conformers of thiacyclohexane-1-oxide with equatorial and axial positions of the S=O bond can be explained by dipole-dipole interaction. © 1971 Consultants Bureau

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