Fractions of chelate hydrogen bonded enol tautomers, corresponding to two potential minima in intramolecular hydrogen bond, are estimated from 13CNMR spectra of solid and dissolved compounds with 1,3-dicarbonyl fragments. For most of them such tautomerism has not been investigated so far. Two crystalline substances were probed at various temperatures, and specific temperature dependences of chemical shifts were observed, reflecting the growth of the main tautomer fraction on cooling. In acetyldibenzoylmethanes, H-chelate tautomers with the enolyzed benzoyl group (hydrogen-bonded to the acetyl group) appears to dominate strongly in both solutions and solid state.

Data on the fast enol-enol equilibria in cis-enol forms of 1,3-dicarbonyl compounds are first collected and analyzed. Intramolecular and external factors determining tautomeric composition are brought to light. These are presented specific temperature dependences of some NMR parameters, reflecting the shift of tautomeric equilibria.

H-1 and H-2 NMR spectra of fractionated poly-gamma-benzyl-L-glutamate solutions are recorded at various temperatures. NMR signals of both these nuclei of solvent molecules ( mixture of CD2Cl2 and CH2Cl2) appear to be doublets. Their splitting (30-130 Hz for protons and 200-600 Hz for deuterons) reduces when the polymer molecular mass grows. As the splitting is proportional to degree of orientation of solvent and solute molecules, it means that longer macromolecules are less oriented than shorter ones. One can explain such behavior in terms of persistent chain model, since the bended rods of less length can be better oriented along the director.

Molecular order in liquid-crystalline solutions of fractionated poly(gamma-benzyl-L-glutamate) is characterized by quadrupole splitting of 2H NMR signal of solvent. The ordering varies sharply as the molecular mass increases from 5 x 10(4) to 1 x 10(5), and the variation pattern is less steep at higher molecular masses. Heating causes reversible disorientation of the molecules of solvent. These data agree with results of 1H NMR studies of unfractionated poly(gamma-benzyl-L-glutamate) and qualitatively correlate with the calculated influence of molecular mass on the ordering of wormlike polymer chains.

Thermotropic main-chain LC polyesters have been studied with the aid of IR and NMR spectroscopy. Rigid mesogens and mesogens with a possibility of conformational isomerism were examined. The dependence of the order parameters of the mesogens and spacers on the chemical structure of the polymer has been determined. The IR spectroscopy data and the data of the calculation of the possible conformations of the mesogen and the spacer confirm the theoretical predictions about the straightening of macromolecules in the anisotropic melt. Solid-state H-2 NMR spectra show that p-oxybenzoic rings adjacent to a flexible spacer are more mobile than inner terphthalic rings. In decamethylene spacer the contrary holds true: the mobility of inner methylene groups is more marked than that of the alpha-methylene groups bound to the mesogen.

In the H-1 NMR spectra of 2-diethylaminomethyl-3,4,6-trichlorophenol (1) below 260 K, an additional splitting of the CH2 signal was found, which can be ascribed to the hindered nitrogen inversion. In the molecule of the O-methylated derivative (2) this process is fast (on the NMR time-scale) down to 150 K. The frequencies and the activation parameters of the nitrogen inversion in (1) were measured by DNMR, which indicated that the inversion requires a preliminary stage of breaking an intramolecular hydrogen bond. The activation enthalpy, Delta H-inv(double dagger) of the inversion stage was evaluated as 28.5+/-6.7 kJ mol(-1).

The copolymerizations of N-vinylpyrrolidone with N-hydroxyphthalimide and N-hydroxysuccinimide esters of acrylic, methacrylic and crotonic acids have been investigated. The reactivity ratios were determined, and kinetic investigations of the copolymerizations were carried out. It was shown that, by varying the acid component of the monomeric ester, it is possible to obtain reactive copolymers greatly differing in structure.

Molecular dynamics of some mesomorphic main-chain alkylene-aromatic polyesters have been investigated by means of NMR spectra of various nuclei over a wide temperature range. In solid polymers regions of different molecular mobilities coexist and their fractions are determined by the sample temperature and thermal history. The sample annealing leads to the growth of rigid fraction. It as found that below the glass transition temperature the only forms of large-scale mobility are the torsional vibrations and flips of para-phenylene groups, while spacer groups are virtually rigid. Above the glass temperature almost all phenylene rings undergo flipping motions and methylene groups of the spacer take part in complicated motions of both anisotropic and isotropic character.

2H NMR spectra of a selectively deuterated liquid crystalline, polydecamethylene-terephthaloyl-bis-4-oxybenzoate, have been investigated in the temperature range from 25 to 100°C. It was found that polymer regions exist with greatly differing molecular mobility. It was shown that the molecular mobility in the polymer depends on its thermal history. The molecular mobility in an aromatic fragment is caused by the vibrational motions of 1,4-phenylene rings with different amplitudes. The fractions of para-phenylene groups undergoing torsional vibrations with high amplitudes increase with temperature and flips of the central phenylene rings of mesogenic triads are observed. The mobility in aliphatic fragments is due to transgauche isomerization and translation motion with the participation of several bonds.

Radiation copolymerization of N-vinylpyrrolidone with undecylenic and oleic acids was studied. It was shown that the yield of polymer and the rate of copolymerization are essentially a function of the composition of the starting mixture. The maximum molar concentration of carbonyl units in the copolymer is 30%. A random copolymer in which there is nothing next to the standing carboxylic acid units is formed. The relative reactivity of the acids is equal to zero; the reactivities of N-vinylpyrrolidone - 0.61 < r < 0.94 for undecylenic and 0.90 < r < 1.31 for oleic acids - were calculated in consideration of the effect of the next-to-last unit.

The mechanisms of thermal degradation processes in polypromellitimide films were investigated by mass-spectrometric thermal analysis and high-resolution NMR spectroscopy in the solid state. Both the structures of the solid residues of pyrolysis products of the PM polyimide and the process of carbonization proper up to 1200° were studied. It was established that the breaking of the Car-O-Car bond in the diamine moiety is not the primary act of degradation of the molecular structure of the polymer, as might be expected on the basis of the value of the bond energy. The process of intermolecular crosslinking following polymer degradation under high-temperature conditions is completed by the formation of a complex nitrogen-containing heterocyclic structure.

Some investigations of the properties of liquid-crystalline solutions of polyamides have been made by means of high resolution NMR. The influence of magnetic field, polymer concentration and temperature on the orientational factor of the system has been determined. Some aspects of the interaction of polymer chain with the solvent molecules have also been studied.

The 1H NMR spectra of phenols with intramolecular hydrogen bonds OH…O in solutions containing proton acceptors have been studied in the temperature range (200 to 110)K. The kinetic parameters of the reversible process of intramolecular ⇌ intermolecular hydrogen bond were determined.

AbstractTautomerism of aromatic β‐ketoaldehydes p‐XPhCOCH2CHO (1, X = NMe2, OMe, Me, H, Br, NO2), aliphatic β‐ketoaldehydes and benzoylacetaldehyde RCOCH2CHO (2, R = Me, i‐Bu, t‐Bu, Ph), RCOCH(Me)CHO (3, R = Me, Et, i‐Pr) and methyl 2‐formylpropionate MeOCOCH(Me)CHO (4) has been studied by the 1H NMR technique. In basic solvents both cis‐ and trans‐enol forms of these compounds co‐exist. trans‐Enolisation, which occurs exclusively at the formyl group, is most favoured in compound (4) and least favoured in compounds (1) and (2). The increasing electron‐attracting property of the substituent X in the aromatic β‐ketoaldehydes (1), as well as increasing solvent basicity in the series propanediol‐1, 2‐carbonate, acetone < dimethylformamide < dimethylacetamide < pyridine, also shifts the equilibrium towards the trans‐enol form. The trans‐enol form is absent in aprotic solvents of low basicity such as CCl4, C2HCl3 and toluene. The thermodynamic parameters of the cis‐trans‐enol (C ⇌ T) and cis‐enol‐enolic (C ⇌ C') equilibria have been estimated from the temperature dependences. The transition from the cis‐to the trans‐enol form is accompanied by an entropy decrease of about 10 cal mol−1 degree−1. Nevertheless the trans‐enol form is stabilised due to its lower enthalpy. The cis‐trans‐enol equilibrium is determined by the relative strength of the intramolecular hydrogen bond in the cis‐enol form and the intermolecular hydrogen bonds with basic solvent molecules of the trans‐enol form.The enthalpy difference of the two cis‐enolic forms does not exceed 1.0 kcal/mol, in rough agreement with the data calculated by the CNDO/2 approximation. Polar solvents favour the hydroxymethyleneketone form (C) for both groups of compounds 2 and 3. The content of the hydroxymethyleneketone form is about the same within series 2 where R = Me, i‐Bu, Ph and is a little higher for the t‐Bu derivative. A decrease of temperature only slightly shifts the equilibrium of compounds 1 and 2 to the hydroxymethyleneketone form, while in the case of 2‐methyl‐β‐ketoaldehydes (3) this effect is markedly pronounced.