N. N. Chipanina

(Aroyloxymethyl)trifluorosilanes: a new class of pentacoordinate silicon compounds

Abstract A new class of organosilicon compounds containing a pentacoordinate silicon atom, (aroyloxymethyl)trifluorosilanes (AFS), has been prepared. The presence of an intramolecular coordinate F3Si ← OC bond is supported by X-ray diffraction, IR spectroscopy and dipole moment data. Si ← O coordination in AFS has been shown to remain intact in the gaseous and liquid states below 420 K as well as in solution in most organic solvents. The dielectric constant of the medium significantly affects the nature of the coordinate Si ← O bond and that of the SiF, CO, COC bonds. In pyridine the intramolecular coordinate Si ← O interaction is disturbed or greatly weakened. At 420–500 K a reversible reaction takes place: ArC OOCH 2 Si F3 α ArCOOCH2SiF3 The changes in enthalpy and entropy are equal in this case: −△H  8.1 ± 0.7 kcal/mol; −°S  15.3 ± 0.8 e.u. T  450 K An assignment of bands in the IR spectra of AFS resulting from vibrations of atoms in the SiF3, >CO and COC groups is given. The electron impact-induced primary disintegration of the molecular ion 4-XC6H4COOCH2Si mainly involves abstraction of a fluorine atom.

Intramolecular coordination in methyl(aroyloxymethyl)fluorosilanes

Abstract The IR spectra of solutions of methyl(aroyloxymethyl)fluorosilanes, C 6 H 5 -COOCH 2 Si(CH 3 )F 2 (I), 4-CH 3 C 6 H 4 COOCH 2 Si(CH 3 )F 2 (II), C 6 H 5 -COOCH 2 Si(CH 3 ) 2 F (III) in 11 solvents in the temperature range 223–363 K, and in the gaseous state have been studied. The molecules of the above compounds display an intramolecular coordination between silicon and oxygen of the carbonyl group. Unlike (aroyloxymethyl)trifluorosilanes [1], there exists the equilibrium between the molecules with and without Si ← O bonds in the solutions of I–III. The proportion of intramolecularly coordinated molecules is greater in solvents of low polarity. This is determined not by enthalpy (Δ H ) values of the Si ← O bond, but a change in the entropy (Δ S ) of the system upon coordination. The coordinate Si ← O bond becomes stronger with increasing number of fluorine atoms in the molecule. A strong dependence of the spectroscopic parameters characterizing the intramolecular coordination on the dielectric constant and the solvent refractive index has been established.

Intramolecular coordination in molecules of C6H5COOCH2CH2SiX3 (X = F, Cl)

Silicon-substituted 2-benzoyloxyethylsilanes, C6H5COOCH2CH2SiX3 with X = F, Cl, OCH3 or 13(OCH2CH2)3N, have been synthesized for the first time. The molecules of compounds with X = F and Cl may exist in two forms, acyclic with a tetracoordinated silicon atom and cyclic with a six-membered ring and a pentacoordinated silicon atom. The cyclic form of the molecules C6H5COOCH2CH2SiX3, with X = F, Cl, are present in solutions of these compounds in non-polar solvents, the proportion increasing with decreasing temperature.

Quantum chemical study of silicon pentacoordination in (Aroyloxymethyl)trifluorosilanes and their analogs

Pentacoordinated silicon compounds of the series 4-XC6H4C(O)O(CH2)mSi(CH3)3-nFn (m = 1, 2; n= 1,2,3) with an intramolecular 0→Si bond are studied by ab initia and semiempirical (AMI) quantum chemical methods. The results are compared with published experimental data. The C6H5C(O)OCH2SiF3 molecule is calculated in an RHF approximation using the 6–31G*basis set. The total energy of the molecule for its geometry optimization is calculated by the MP2 method including electron correlation. This leads to considerably improved agreement between the calculated coordination energy (25.3 kJ/mole) and the experimental value (28.5 kJ/mole). The geometry and the dipole moment calculated by both ab initio (HF/6-31G*//HF/6-31G*, MP2/6-31G*//MP2/6-31G*) methods and by the AMI method are in satisfactory agreement with the experimental data.

AM1 studies of photoelectron spectra

Deep-lying π- and σ-orbitals of 10-alkylphenothiazines were studied by photoelectron spectroscopy and quantum-chemical AM1 calculations. It was demonstrated that in 10-ethylphenothiazine the lone electron pair of the S atom interacts with the π-system of the aromatic fragments. The π-MOs, whose energies are a function of the dihedral angle between the planes of the benzene rings of phenothiazines and are independent of the degree of pyramidality of the N atom, were found. The differences in the energy of these MOs were used for estimating equilibrium dihedral angles of tricyclic molecules in the gaseous phase. These values differ only slightly from those observed in the solid phase. The replacement of the hydrogen atom at position 10 by the methyl group leads to a decrease in the dihedral angle, leaving the orientation of the substituent unchanged. The orbital energies of phenothiazines, which were calculated by the AM1 method, adequately reflect the order of changes in the ionization potential. However, contributions of the two highest occupied π-MOs to the total charges on the N and S atoms are inconsistent with the experimental data.

Tautomeric transformations of arylidenebarbiturates in solutions

IR and UV spectroscopy and quantum chemistry were employed to investigate the structure of arylidenebarbiturates able to undergo tautomeric transformations. The composition of tautomeric mixtures depends on the properties of the solvent and on the concentrations of the solutions.

Ring-chain transformations of substituted 2-imino-1,3-thiazinoazoles

The ring-chain transformations of substituted 2-imino-1,3-thiazinoazoles in DMSO under the influence of tetraalkylammonium or alkali metal hydroxides were studied by acid-base potentiometric titration and PMR, IR, and UV spectroscopy.

Condensation reactions of vinyl and ethyl derivatives of 2-amino-and 2-formylimidazoles

New Schiff bases of 1-vinyl- and 1-ethyl-substituted imidazoles and benzimidazoles were synthesized. The condensation reactions of 2-amino- and 2-formylimidazoles with 2-aminobenzimidazoles are virtually independent of the nature of the substituent (CH=CH2 or Et) at position 1 of the heterocycle. The structures of the azomethines synthesized were established by1H NMR and IR spectroscopy.

The interactions of (=O→Si)-(benzoyloxymethyl)trifluoro-and -(benzoyloxymethyl) methyldifluorosilanes with a solvent

The IR spectra of solutions of (=O→Si)-(benzoyloxymethyl)trifluorosilane (1),-(benzoyloxymethyl)methyldifluorosilane (2), and butyl benzoate (3) are examined in the region of thev(C=O) stretching vibrations in 24 solvents. The ability of compounds1—3 to undergo specific intermolecular interactions is evaluated from the dependence ofv(C=O) on the Kamlet-Taft (π*,α, β) parameters, which was obtained for the carbonyl groups involved in the intramolecular coordinate (=O→Si) bond and for free carbonyl groups. The corresponding values of the coefficients in the Kamlet-Taft equations are indicative of a weak ability of pentacoordinate silicon compounds1 and2 to undergo acid-base interactions.

Reaction of aminopyridines with acetylene

Conclusion1.2-Aminopyridine and acetylene react under pressure and in the presence of KOH to form 2,3-dimethylimidazo[1,2-a]pyridine.2.2-and 4-aminopyridines and 4-aminoquinoline in water or aqueous dioxane react with acetylene under pressure in the presence of cadmium acetate giving, respectively, 1-vinyl-2-and 1-vinyl-4-pyridones and 1-vinyl-4-quinolone.