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

Fourier transform IR spectra and structure of 2-substituted 1-nitro- and 1-bromo-1-nitroethenes

Molecular structure and vibrational spectra of 2- trichloromethyl(ethoxycarbonyl)-1-nitroethenes and 2- trichloromethyl(ethoxycarbonyl)-1-bromo-1-nitroethenes were calculated in terms of the density functional theory (B3LYP/6-31G*). The experimental FTIR spectra of these compounds in the range from 4000 to 400 cm-1 were interpreted in detail on the basis of the calculation data. 2-Substituted 1-nitro- and 1-bromo-1-nitroethenes were assigned the structure with trans orientation of the nitro and trichloromethyl (or ethoxycarbonyl) groups, and the ethoxycarbonyl derivatives were assumed to exist in equilibrium between s-cis and s-trans conformers. © 2007 Pleiades Publishing, Ltd

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

Intra- and intermolecular interactions in the series of acyclic and macrocyclic compounds containing nucleotide bases and their derivatives

Intra-and intermolecular interactions in acyclic compounds containing nucleotide base (uracil and thymine) derivatives and their macrocyclic analogs (pyrimidinophanes) were studied by IR, UV, luminescence, and NMR spectroscopy. Molecules of these compounds include one or two N3-methylsubstituted or N3-unsubstituted uracil fragment or two adenine fragments linked through a hexamethylene spacer to an uracil, 5,5'-methylenediuracil or diphenylmethane fragment. The examined compounds almost all are characterized by π-π interactions and intramolecular hydrogen bonding between the terminal uracil or adenine fragments. Intramolecular association constants were determined and factors affecting them were discussed. Complex formation of acyclic and macrocyclic ligands with adenine and thymine derivatives was studied. The low values of the association constants were interpreted in terms of a competition between intra-and intermolecular bonding and very labile ligand structure. © 2007 Pleiades Publishing, Ltd

Isomerism of certain derivatives of benzalacetophenone

1. p-Nitro-, m-nitro-, and p-chlorobenzalacetophenone (mp 113-114°C) have a trans-configuration of the ethylenic bonds and represent the s-cis-conformer both in solid form and in solution, with a possible admixture of the s-trans-isomer in solution. 2. p-Chlorobenzalacetophenone with mp 79-80°C is a cis-isomer with a negligible admixture of the trans-form and exists in the solid state as the s-cis-conformer. © 1969 Consultants Bureau

IR and NMR spectra, intramolecular hydrogen bonding and conformations of mercaptothiacalix[4]arene molecules and their para-tert-butyl-derivative

It is demonstrated that the introduction of p-tert-butyl groups dramatically influences the conformational behaviour of the mercaptothiacalix[4] arene molecules. Quantum-chemical computations in combination with IR and NMR spectroscopy prove that, in contrast to closely related calixarenes, the 1,3-alternate becomes a dominant conformer of p-tert-butyl-mercaptothiacalix[4] arene not only in crystal, but also in solutions and in vacuum. It is shown that the title molecules form essentially non-cooperative intramolecular hydrogen bonds: their SH groups are intramolecularly H-bonded solely to the sulfide groups bridging thiophenolic units. The enthalpy of this bonding, evaluated from Iogansen's rule, amounts to ca. 1.5 kcal mol-1 per one SH•••S bond, which about four times smaller than the enthalpies of cooperative intramolecular H-bonds formed by related calixarenes and thiacalixarenes. © 2007 Springer Science+Business Media B.V

Dipole moments and molecular spectra of certain derivatives of dibenzalacetone

From the spectral data it may be assumed that di-p-chlorodibenzalacetone exists in solution as a mixture of s-cis,s-cis- and s-cis, s-trans-conformations, possessing a trans-configuration of both ethylenic bonds, which does not contradict the data of the dipole moments. © 1970 Consultants Bureau

Spectroscopic studies of compounds containing a P —H bond: 4. Vibrational spectra and conformational multiformity of di- tert-butylphosphorous acid molecules

IR and Raman spectra of liquid di- tert-butylphosphorous acid and its two low-temperature crystalline modifications are studied. It is found that at least three stable conformations of acid molecules can exist in the liquid state. © 1995, Plenum Publishing Corporation. All rights reserved

Three-dimensional structure of phosphorus-containing heterocycles Communication 33. Oxides and selenides of 2-phenoxy-5,5-dimethyl-1,3,2-dioxaphosphorinanes

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 the π-electrons of the benzene ring is hindered. © 1985 Plenum Publishing Corporation