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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.

An additive system of polarities in 12H-dibenzo(dinaphtho)[d,g][1,3]dioxocins is proposed, and alkyl—oxygen and phenyl—oxygen group dipole moments in these compounds were determined. The stereospecific relation of the polarity of the Csp2-O bond to the mutual orientation of p orbitals of unshared electron pairs of oxygen atoms and π orbitals of the aromatic ring is shown.

An x-ray structural investigation of the synthesized title compounds (1) and (2) has been performed. The heterocycle of 1 has a boat-chair conformation with the P2=O2 bond in the axial position. The heterocycle of 2 has a distorted-boat conformation with the C6=O carbonyl in the plane of one of the fused benzene rings. The P2=O2 bond is in a pseudoequatorial position.

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.

1H NMR spectroscopy, measurements of dipole moments, and the Kerr effect have been used to study the conformational structure in solutions of 3-X-3-oxo-6,7-benzo-1,5,3-dioxaphosphepines (X=Me, Et, Ph, Cl, NEt2, OEt, OPh). On the basis of x-ray diffraction data, by means of the Dillen-Geise method, possible conformers of the seven-membered ring have been described quantitatively: chair, twist, and twist-boat. It has been shown that the compounds are characterized by a three-component equilibrium of chair and flexible forms. The relative populations of the conformers depend on the nature of the substituent X. The relationships in internal rotation around the P-Ph and P-O(R) bonds are discussed.

2-Phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepine exists in a melt and solutions in polar solvents as a three-component equilibrium of two chair forms (C) with axial and equatorial arrangement of the phenyl group and the twist-boat form (TB) with a pseudoequatorial position of the phenyl substituent, a-C ⇄ e-C ⇄ e-TB. The two-component equilibrium e-C ⇄ e-TB is observed in nonpolar solvents. The e-TB conformation occurs in the crystalline state. The dipole moment of the P=O groups is 3.5 D. The angle of rotation of the plane of the phenyl group with respect to the P=O bond in the e-TB conformation was 54 or 129‡.

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.

1H and31P dynamic NMR, vibrational spectroscopy, and consideration of dipole moments have shown that 2-chloro-2-thiono-4,5;7,8-dibenzo(4,4′-dimethyl-6,6′-di-tert-butyl)-1, 3,2-dioxaphosphocene and its 2-ethoxy derivative are conformationally heterogeneous. The former exists as a three-component equilibrium mixture, and the latter as a two-component equilibrium mixture. In the chlorothiophosphate the boat-chair conformation predominates, with equatorial location of thiophosphoryl; next in frequency is boat-chair with axial orientation of P=S, and third is the deformed boat form. In the ethyl thiophosphate the preponderant form is the deformed boat with thiophosphoryl in the equatorial position.

5,5- Dimethyl-2-thio-2-phenoxy- and 5,5-dimethyl-2-thio-2-ethoxy-1,3,2-dioxaphosphorinanes exist in the liquid state and in solution in a three-component equilibrium featuring two chair forms with equatorial orientation of the P=S bond differing in the orientation of the OPh or OEt groups and a chair form with an axial P=S bond. The P=S bond in 4-methyl-2-thio-2-phenoxy-1,3,2-dioxaphosphorinane occupies the equatorial position.

The seven-membered heterocycle in the crystal structure of 2-phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepine has distorted (asymmetric) twist conformation and the plane of the phenyl substituent at the phosphorus atom does not coincide with the bisector of the plane of the OPO fragment of the heterocycle and is not perpendicular to it.

General conclusions on three-dimensional structure of 8-membered phosphorus rings are given in terms of the effects produced by the exo- and endo-cyclic heteroatoms, planar fragments, their number and localization. The role of anomeric effect in determination of exocyclic substituent orientation in 6-, 7-and 8-membered cycles is considered. The influence of stereoelectronic interactions in the conformational behavior as well as further prospects in this expanding field are discussed.

To investigate the features of conformational behavior for phosphorus-containing seven-membered ring we have synthesized the following compounds: The study of the three-dimensional structure was carried out by means of IR, photoelectron and dynamic NMR spectro-scopy, and electro-optical methods; the x-ray data and theoretical calculations were also taken into consideration. The three-dimensional structure of these compounds is characterized by parameters like ring conformation (chair, boat, twist or twist-boat), axial or equatorial position of exocyclic substituents on phosphorus atom, and rotational orientation of irregular substituents (OAlk or OAr). We have analyzed various spectral tests for conformational study of these species on the basis of conformational composition in different media that promoted the investigation of complex three- and four-component conformational equilibria. All results are discussed in terms of modern theoretical conceptions of stereochemistry.

The Raman and IR spectra of 5,6-benzo-1,3,2-dloxaphos-phepines have been studied In the solld and liquld states, In solutions of dlfferent polarity, the temperature and concentration being varied. The asslgnments of the spectra have been made, The main spectral features that depend on molecular conformatlons are the Intense highly polarized lines of the symmetrlc vlbrations (“breathIng”) of the seven-membered ring In the 700–800 cm−1 region, νp=x(X=S, Se) ad 530–650cm−1, the vibrations of o-xylllenlc fragment in the regions of 1050–1070 cm−1 (δc=c-c) and 1200–1220 cm−1 (νc=c-c). The δc=c-c and νc=c-c vibrations appeared to be a reliable conformatlonal test for the Identification of the chair and twist forms, the frequencies being equal to ∼1050 and∼1220 cm−1 In the flrst case and ∼1070 and∼1200 cm−1 In the second. As for the equlllbrium of the chair-like forms the frequencies of the axlal P=X bonds are always lower than the equatorlal. For most of the compounds the complex three and even four-com...

According to the data from x-ray crystallographic analysis, the molecule of 2-diethylamino-4,5,7,8-dinaphtho[1,2:1′,2′]-6.H-1,3,2-dioxaphosphocin has an unsymmetrical boat conformation with dialkylamlno group in the equatorial position and with greatly elongated endocyclic P-O bonds (to 1.667 A).

1. Dipole moments and polarizability ellipsoids have been determined for the phosphorus bonds in 2-phenoxy-1,3,2-dioxaphosphorinanes. 2. It has been shown that the phenoxy groups in these compounds have cis-axial orientation, the plane of the benzene ring standing at right angles to the P-O-CAr bond plane.

The 13C and dynamic 1H NMR spectroscopy were employed to derive spectral tests for conformational studies of eight-membered phosphorus (PIII and PIV) containing heterocycles: 4,5; 7,8-dibenzo-(I) and dinaphto-(II) 1,3,2-dioxaphosphocines. Passing from series (I) to (II) causes a dramatic change in the shift difference of methylene protons at C-6. The geminal 2 J(HH) and long-range 5 J(PH) spin-spin couplings are determined by the ring structure. The latter is also influenced by the phosphorus valence state and the orientation of substituents at phosphorus. Fairly definite stereo-chemical assignments can be made using the n J(31P13C) couplings with n of 2 to 5.

1. Reaction of (α-hydroxyalkyl)phenylphosphines with phenylboric anhydride has given 4,6-disubstituted-2,5-diphenyl-2-bora-1,3,5-dioxaphosphorinanes. 2. The spatial structures of the products have been determined, and the equilibrium amounts of the stereoisomers measured.

Sulfides and selenides of 4,6-disubstituted 2,5-diphenyl-2-bora-1,3,5-dioxaphosphorinanes were obtained. The positions of the equilibrium and structures of the stereoisomers of these compounds were determined.

The dipole moments and polarizability ellipsoids of phosphorus-containing bonds in 2,6,7-trimethyl-4-methyl-2,6,7-triaza-1-phosphaicyclo[2.2.2]octane (3) and its 1-oxide (4) and 1-sulfide (5) and in 2-dimethylamino-1,3,2-dioxaphosphorinane (2) have been determined from dipole moment, Kerr effect and depolarization of Rayleigh scattering measurements. The conformational rigidity of bicyclic compounds such as (3–5) as well as of several 2-oxo-2R-4,6-dimethyl-1,3,2-dioxaphosphorinanes are utilized in considering the implications of assuming that the component moments are primarily directed along the phosphoryl bond.

1. An analysis of the temperature dependence of the Raman, IR, and PMR spectra and dipole moments of the oxide, sulfide and selenide of 2-phenoxy-5,5-dimethyl-1,3,2-dioxaphosphorinane showed that going from this oxide to the sulfide and selenide is accompanied by a shift in the conformational equilibrium from the ananchimerically displaced equilibrium in the oxide to the presence of both chair forms in the sulfide and selenide. The form which axial, gauche orientation of the phenoxyl group predominates. The less populated conformer has chair form with an equatorial, gauche phenoxy group. 2. The UV spectral data indicates that the structure found in the oxide and selenide are such that p-π conjugation of the unshared p electron pair of the exocyclic oxygen atom which theπ-electrons of the benzene ring is hindered.

A chair conformation with an axial orientation of the phosphoryl or thiophosphoryl group is preferable for 2-dimethylamino-2-oxo- and-2-thiono-1,3,2-oxathiaphosphorinanes. The cis isomer of 2-dimethylamino-2-oxo-4-methyl-1,3,2-oxathiaphosphorinane has a similar structure with an equatorial orientation of the 4-methyl group, while the corresponding sulfide is characterized by a trans configuration with a reoriented positioning of the substituents attached to the phosphorus atom.

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.

X-ray structure analysis shows that for 4,5;7,8(4′,4″ -dimethyl-6′,6″-di-tert-butyl)-dibenzo-6H-2-diethylamino-2-thiono-1,3,2-dioxaphosphocine, the boat-chair conformation of Cs symmetry with an equatorial diethylamino group occurs in the crystal.

We determined the conformational free energy of a phenyl substituent on a tri- and tetracoordinated phosphorus atom in a 2,4,6-trimethyl-1,3,5-dioxaphosphorinane ring.

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 ?-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 ?-orbitals of unsaturated systems) and the acceptors (bonds of the phosphorus atom) has been proved. The bibliography contains 193 references.

Molecules of 2-dimethylamino-5,6-benzo(4,7-dihydro-1,3,2-dioxaphosphepin have two theoretically possible conformations: chair (C) and twisted boat (TB), The population of the TB form depends on the coordination of the phosphorus atom and increases in the order 0 < S < UEP, and also upon going from the benzo to the ethylene derivative. The latter is connected with the change in the torsional strain energies.

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\(P - O - C_{sp^2 } \).

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.

1. The reaction of 2,4,6-triisopropyl-1,3,5-dioxaphosphorinane with phenyl azide yields 5-phenylamino-2,4,6-triisopropyl-1,3,5-dioxaphorinane and 5-phenylimino-5-phenylamino-2,4,6-triisopropyl-1,3,5-dioxaphosphorinane in yields depending on the reagent ratio. 2. The stereoisomer with axial orientation of the amino group predominates in the equilibrium of 5-phenylamine, 5-diethylamino-, 5-piperidino-, and 5-morpholino-2,4,6-triisopropyl-l,3,5-dioxaphosphorinane and their sulfides.

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.

1. 2-Phenoxy-2-oxo(thiono, seleno)-5,6-benz-1,3,2-dioxaphosphepines in solutions of nonpolar solvents are characterized by an equilibrium of two chair-like forms, which in the case of the sulfide and selenide is shifted in the direction of a conformer with an equatorial orientation of the phenoxyl group; in the oxide, at equilibrium, the proportions of two conformers are approximately the same. In solutions of polar solvents, a three component equilibrium is observed for the oxide, in which the flexible forms as well as the chair-like forms are present. 2. In accordance with the dipole moments and Kerr effect data, in all conformations, the compounds studied are characterized by a gauche conformation of the phenyl group in relation to the P=O (P=S, P=Se) bond and by an orthogonal disposition of the benzene ring π-orbitals and the p-unshared electron pair on the exocyclic oxygen atom.

Hydroxymethyldiphenylboryloxymethylphenylphosphine and 2,5-diphenyl-2-bora-1,3,5-di-oxaphosphorinane, in which the phenyl group at the phosphorus atom is predominantly found in the axial position, are formed in the reaction of di(hydroxymethyl)phenylphosphine with isobutyl diphenylborate.

An investigation of the PMR spectra over a wide temperature range in different solvents, the dipole moments, and the Kerr constants of 2-dialkylamino-1,3,2-dioxaphosphepanes with a planar group of atoms in the heterocycle (benzene ring, multiple bond) has demonstrated the existence of a conformational equilibrium between the chair form with equatorial position of the dialkylamino group and the twist form.

1. The structure of 5-substituted 2,2-dimethyl-1,3,2-dioxasilanes was studied by the methods of dipole moments and PMR spectroscopy. The compounds have a predominant chair conformation. 2. In the case of 2,2-dimethyl- and 2,2,5-trimethyl-5-nitro-1,3,2-dioxasilane, a conformational equilibrium can exist, strongly shifted in the direction of the conformation with an axial nitro group.

Using PMR spectroscopy and the dipole moment and Kerr effect methods it has been shown that 2-methoxy-5,6-benzo-1,3,2-dioxaphosphepine oxide and sulfide are characterized by solution equlibria involving two chair-like (C) conformers e-C ⇄ a-C, which are shifted in favor of the e-C form; in the case of an equatorial orientation of the methoxy group equilibrium involves the gauche and anti rotamers, while in the case of an axial orientation (of the methoxy group) the gauche rotamer of the methyl group relative to P=O or P=S bond is stabilized. The presence of a twist conformer in the case of the oxide cannot be precluded from consideration.