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A number of 2-methylthio-6-methyl-4-alkyl- and alkylaminopyrimidines, as well as their salts produced by the reaction with methyl p-toluenesulfonate and trifluoroacetic acid, were investigated. The quantum chemical and experimental IR and Raman spectral methods were used to determine the preferential isomeric forms of the molecules of studied compounds, whose convenient spectral markers were revealed. The starting pyrimidines and their salts were found to exist predominantly as an amino form. The salt formation proceeds via the methylation (protonation) of the N1 atom of pyrimidine ring.

Replacement of terminal atoms of Br in 1,3-bis(bromopentyl)-5(6)-substituted uracils with 2-mercapto-5-methyl-1,3,4-thiadiazole, 2,5-dimercapto-1,3,4-thiadiazole, 2-mercaptoimidazole, and 2-mercaptobenzimidazoles resulted in a series of acyclic compounds and isomeric heterocyclophanes. Structures of macrocyclic regioisomers were unambiguously determined by NMR data. One of the regioisomers exhibits a hypochromic effect with respect to model compounds. The acyclic uracils obtained bridged with five-membered heterocycles are alkylated with methyliodide and methyl tosylate, and oxidated with m-CPBA, H2O2, and I2.

Reaction of α,ω-bis(3,6-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl)alkanes with paraformaldehyde leads to pyrimidinophanes, which contain four 3,6-dimethyluracil fragments, connected to each other by the methylene chains. A comparative study of intra- and intermolecular interactions of “open” and macrocyclic uracil derivatives in the crystal state and in solution was performed. According to the NMR spectroscopy data, there is no self-association of “open” and macrocyclic compounds in chloroform solutions, whereas the X-ray data revealed the intermolecular π-π contacts between the 3,6-dimethyluracil fragments in the crystals of these compounds. Conclusions on the presence of intramolecular interactions in chloroform solutions of α,ω-bis(3,6-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl)alkanes and pyrimidinophanes were made based on the UV spectra, which were interpreted in terms of hypo- and hyperchromic effects relatively to the model uracil derivative. These conclusions correlate with the X-ray data: there are no intramolecular π-π contacts between the 3,6-dimethyluracil fragments both in the crystals and in solutions of “open” compounds, positions of these fragments relatively to each other in the molecules of pyrimidinophanes are defined by the lengths of the polymethylene bridges. The intramolecular stacking effect between the opposite uracil rings is observed for the macrocycles with trimethylene and hexamethylene chains, whereas there is no such interactions in pyrimidinophanes with tetramethylene chains.

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.

The oxidative dehydrocyclization of the 3-(indolizin-2′-yl)-2-oxoquinoxaline monopodand performed either electrochemically or under the action of molecular iodine affords new redox-active heterocyclophane consisting of the redox-switchable biindolizine fragment combined with the polyether-bridged π-deficient quinoxaline systems. The single-crystal X-ray diffraction study showed that the trioxaundecane chain of heterocyclophane adopts an extended conformation, and one of the phenyl substituents of the molecule closes the pseudocavity formed by the spacer from one of the sides. The cyclic voltammetric study of heterocyclophane in MeCN and DMF showed the three-step oxidation of the indolizine fragments accompanied by the single-electron transfer in each step. The first and third steps are reversible, and the second step is irreversible. The oxidation at potentials of the first peak gives rise to stable radical cations detected by the ESR method (g = 2.0024, a 2N = 0.26 mT).

The IR and Raman spectra and conformations of the ionic liquid 1-ethyl-3-methyl-1H-imidazolium tetrafluoroborate, [EMIM][BF4] (6), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM+ (.) BF4- ion pair closely resemble those of the isolated ions EMIM+ and BF4-, except for the antisymmetric BF stretching vibrations of the anion, and the out-of-plane and stretching vibrations of the H-C(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion-pair formation is the H-bonding between H-C(2) and BF4-. However, these weak H-bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD2Cl2 Solutions. According to the 'gas-phase' computations, in these associates, the BF4- anion is positioned over the imidazolium ring of the EMIM+ cation and has short contacts not only with the H-C(2) of the latter, but also with a proton of the Me-N(3) group.

A series of conformationally heterogeneous and energetically multilevel ω-diphenylphosphoryl- and ω-diphenylthiophosphoryl-substituted aliphatic alcohols, whose molecules are capable of five-, six-, and seven-membered ring closure due to the OH...O=P or OH...S=P intramolecular hydrogen bond (IHB), was studied by IR spectroscopy and molecular mechanics. The data obtained confirm the previous assumption that the energy of IHB (E IHB) differs substantially from the difference of enthalpies of conformers with and without IHB (–ΔH ), which is experimentally determined by the temperature dependence of the intensity of IR ν(OH) absorption bands. The measured –ΔH values can be positive, zero, or negative at significant IHB effects, i.e., at high Δν(OH) and E IHB values.

The conformations and vibrational spectra of 2-benzylphenol have been analysed within the framework of scaled quantum mechanics. It is shown that the solid-state conformation of the 2-benzylphenol molecule corresponds to one of four potential energy minima predicted by non-empirical quantum chemical calculations for the isolated molecule. In the molten state and in diluted CCl4 solutions of the title compound this conformer coexists with another two spectroscopically detected conformations. The presence of several conformers gives rise to the observation of the corresponding number of vsCH2 and vasCH2 bands in the IR spectra, thus providing experimental evidence of the conformational sensitivity of the vCH2 frequencies. It is shown that vCH2 wavenumbers of different kinds of molecules, containing diphenylmethane fragments, are determined by the dihedral angles between the planes of the aromatic rings and the plane of the connecting methylene bridges, except for the case of short intramolecular contacts with the participation of the methylene protons.

IR and Raman spectroscopy, normal coordinate analysis, and molecular mechanics were used to study the conformations of Cl(CH 2 ) 2 O–PCl 2 molecules. It is shown that gauche conformations of the Cl–CH 2 –CH 2 –O residue are energetically preferred in liquid. These are the only conformations remaining in the low temperature crystals, anti conformations being “frozen out”. In these crystals the POCC residue most probably adopts an extended conformation, the OC bond being in anti-position relative to the phosphorus lone pair. In the liquid state the extended conformers coexist with the convoluted conformations. Contrary to what might be expected from molecular mechanics considerations the latter conformers are practically as energetically stable as the former. The gap between experimental measurements and the respective molecular mechanics’ estimation is attributed to certain attractive intramolecular 1–5 interactions between the phosphorus and the chlorine atoms. It is used for rough quantitative evaluation of the energy of these interactions, which amount to ∽10–15 kJ mol −1 .

2,4,6-Tris(3,5-di-tert-butyl-4-hydroxybenzyl)resorcinol in the crystal and in solution has a similar steric structure, favorable for its performance as peroxyl radical scavenger.

IR and Raman spectra of 1,4-butanediol (BD) versus variations in the medium (CCl4, CH3CN), concentration, temperature, and phase state were obtained. The observed changes attest to the conformational variety of BD molecules under the experimental conditions. On the basis of the analysis of the v(OH) region it is concluded that both in the gas phase and in CCl4 solution conformers of BD with free OH groups coexist with conformers with O-H...O intramolecular hydrogen bonds. The difference in enthalpies, ΔH, for the groups of conformers with and without intramolecular hydrogen bonds was found from the temperature dependence of the v(OH)free and v(OH)intra band intensities. The structures and energies for 70 possible spectrally and energetically distinguishable conformers of BD that do not take into account intramolecular hydrogen bonds were calculated by molecular mechanics with account of electron lone pairs of oxygen atoms. Using the experimental values of ΔH and the calculated relative conformer energies,E, the intramolecular hydrogen bond energyEintra= 3.7 kcal mol−1 was found.

Conformational differences in molecules of 1,3-propanediol with variations of medium, temperature, and phase composition appear in their IR and Raman spectra. In the gas phase and in dilute solutions of 1,3-propanediol in CCl4 forms with intramolecular hydrogen bonding (IHB) and without it exist in comparable amounts. The difference in the weighted mean energies of the corresponding groups of conformers was found from the temperature dependence of the intensities of the bands for free νOH and bounded νOH. By calculating the conformational term of ΔE* and by using the energy values of the 25 conformers of the diol molecules, calculated by molecular mechanics methods, the IHB energy was determined for two of them.

The IR and Raman spectra and conformations of calix[4]arene, thiacalix[4]arene and their p-tert-butyl derivatives have been analysed within the framework of scaled quantum mechanics (SQM). It is shown that the introduction of four p-tert-Bu groups into the calixarene molecules influences the relative energies of their conformers and the enthalpy of the cooperative intramolecular H-bonding (DeltaH(intra)) almost negligibly. DeltaH(intra), evaluated from Iogansen's rule, amounts to approximately 26-28 kcal mol(-1) for the calixarenes and approximately 20-21 kcal mol(-1) for the thiacalixarenes, which essentially exceeds the enthalpies of non-cooperative H-bonds formed by related phenols. As a result of this strong bonding, bands of stretching, bending and torsion vibrations of an eight-membered cyclic system (OH...)4 arise, e.g., two delta(OH)4 bands are observed in the IR spectra of the most highly symmetric C4 cone conformations of calix[4]arene and thiacalix[4]arene. The "duplication" of the number of OH infrared bands is a good new indicator of cooperativity of intramolecular H-bonding of the calixarenes.

The compounds exhibiting hypervalent interactions of nonbonded atoms may be used as models of prereaction and transition states of nucleophilic substitution reactions. Our studies of the molecules X(CH2)2-O-PCl2 (X ˭ H (1); SCN (2); C2H5 (3); CH3O (4); Cl (5) revealed the possibility of subtle intramolecular 1–5 attractions between the sulfur (2) [I] or the oxygen (4) or the chlorine (5) and the phosphorus atoms. The attractions influenced perceptibly only the energy of the conformers with intramolecular contacts between the heteroatoms. A substantial energetical preference of the convoluted conformers (B) in the liquid state was observed in the case of 2. 4 and 5. In contrast. the molecules 1 and 3 preferred to exist in liquid in extended conformations (A). These dramatic changes cannot be explained by steric reasons or Coulomb attractions, and thus were attributed to hypervalent attractions between the heteroatoms. The relative energies of (A) and (B) conformers were used in quantitative assess...

1. The assignment of the bands and the lines in the vibrational (IR, Raman) spectra of vinyldichlorophosphine oxide (VDCPO) was refined by normal-coordinate analysis. 2. The conformational nonuniformity of VDCPO was established on the basis of an analysis of the dependence of the spectra on the phase state, the temperature, the polarity of the solvent, and the concentration of the solutions. In the liquid and in the gas VDCPO exists in an equilibrium between two forms, of which at least one is unsymmetrical. In the more stable and less polar conformer (which remains in the crystal) the C=C and P=0 double bond are close to eclipsing, while in the other they are opened up. 3. In addition to the conformational nonuniformity, the signs of intermolecular effects appear in the spectra of the liquid and the solutions.

1. The IR spectra of a solution of mercaptoethanol in CCl4 and in gas-phase mercaptoethanol have νXH bands for free OH and SH groups and OH...S and SH...O groups in intramolecular hydrogen bonds. This indicates a conformational multiplicity of the ME molecules. 2. A molecular mechanics calculation indicates the possibility of conformational multiplicity for mercaptoethanol. The energy of the intramolecular OH...S hydrogen bond was evaluated.

1. The IR, Raman, and UV spectra of a number of derivatives of substituted ethoxyvinylphosphonic and ethoxyvinylphosphonous acids (EPA) were studied. 2. The doublet nature ofνC=C in the spectra of EPA derivatives was explained by rotational isomerism around the C-O bond in the ether fragment of the molecule. The low-frequency component of the doublet was assigned to the cis conformation and the high-frequency component to the gauche conformation. 3. The optical signs of conjugation of the phosphorus-containing groups with a π system increase in the series: P(O)(OC2H5)Cl