J. Lövy

Conformational structure of poly(ethylene terephthalate). Infra-red, Raman and n.m.r. spectra

Abstract Infra-red and Raman spectra of unoriented samples of poly(ethylene terephthalate) in the crystalline and amorphous states and in solution were measured. The dissolved polymer was also studied by n.m.r. spectra. Digital separation of the vibrational spectra of amorphous and crystalline components made possible the detection of some new bands, the interpretation of which is presented. By comparison with the vibrational spectra of model compounds combined with analysis of n.m.r. spectra, the conformational forms present in the amorphous and liquid states of poly(ethylene terephthalate) were characterized and their populations were determined. Bands in vibrational spectra which are characteristic of various conformational forms were defined.

CIDNP study of reactions of ketyls and dianions derived from benzophenone and fluorenone with acetic anhydride

Abstract A study is presented of 1H and 13C CIDNP effects in the reactions of Na and Li salts of ketyls and dianions derived from benzophenone and fluorenone with acetic anhydride in tetrahydrofuran and dimethoxyethane. CIDNP effects were observed for products obtained by mixing of reactants both at high and at low field. Interpretation of the CIDNP effects (mixing at high field) indicates that in reactions of ketyls with acetic anhydride the primary step is O-acylation followed by spin-selective electron transfer between ketyl and O-acylated ketyl. At higher dilution or in the presence of strongly coordinating agents, heterolytic deprotonation of acetic anhydride by ketyl is also observed. CIDNP effects depend on the presence of ketyl which affects the relaxation of sterically accessible nuclei and also suppresses the intensity of ketone signals by rapid electron transfer. In reactions of dianions, electron transfer between dianion and acetic anhydride partly takes place, and the ketyl formed in this way reacts with a further molecule of acetic anhydride.

Conformational study of methylethers of the type CH3OCH2R: an NMR and vibrational spectroscopic study

Abstract Analysis of 13C NMR spectra of methylethers of the type CH3OCH2R, with R = CH3 (I), CH2CH3 (II), CH(CH3)2 (III) and C(CH3)3 (IV) has shown that the trans form strongly predominates on the OCH, bond, the gauche forms appearing only in those cases where close contact between methyl groups can be avoided. Analysis of both 1H and 13C NMR spectra indicates that all staggered forms are populated on the CH2R bond. In vibrational spectra, the strong Raman bands near 800 cm−1 were found to be very sensitive to conformational structure. For I, III and IV, the bands of various conformers in this range are separated, permitting ΔH to be determined.

NMR study of cis3̄trans isomerism in N-methylated lactams with 11- and 13-membered rings

Abstract From 1H-NMR spectra of 1-methyl-azacyclo-undeca-2-one and 1-methyl-azacyclo-trideca-2-one, the bands corresponding to the cis and trans forms have been assigned and analyzed; based on this analysis, conformational structures about the C-C bond next to nitrogen are proposed. By analysis of the relative areas and shapes of the N-methyl bands measured for the two lactams in 1,1,2,2-tetrachloroethane-d2, over a broad temperature range, the equilibrium and thermodynamic parameters characterizing the cis—trans isomerism of the amide bond in these lactams have been determined. Peaks corresponding to the cis and trans forms in the 13C-NMR spectra of these lactams have also been assigned.

Conformational structure of N-methylpropionamide and N-methylisobutyroamede. NMR shift reagent and IR study

Abstract The structures of the stable conformers of N-methyjpropionamide and N-methyliso-butyroamide in CCl4, solution were determined by a combination of IR spectroscopy and NMR spectroscopy with lanthanide shift reagents. N-methyl-propionamide was found to exist in the form of two rotational isomers, 1 and 2, with the ethyl group twisted out of the plane of the amide bond by the angles Ψ = 140 and 20°, respectively. For these two conformers, the enthalpy difference is ΔH = 2.13 ± 0.08 kcal mole−1 and the entropy difference ΔS = 7.81 ± 0.55 cal mole−1 grad−1. N-methylisobutyroamide exists in a single form, with the two C-methyl group positions very close to those found in the two isomers of N-methylpropionamide.

NMR and Raman spectroscopic study of complex formation between 2-methyl-2-azabicyclo-[2,2,2] -octa-3-one and TiCl4

Abstract From analysis of 1 H and 13 C NMR and Raman spectroscopic data, in CDCl 3 and 1,1,2,2-tetrachloroethane- d 2 solution, the lactam 2-methyl-2-azabicyclo-[2,2,2]-octa-3-one (L) was found to form complexes with TiCl 4 (M) of overall composition M 2 L, ML and ML 2 . Two forms of the ML 2 complex were observed by NMR. In all these complexes, Ti coordinates to the carbonyl oxygen, and the metal—carbonyl bond is of the same type. The complexes ML and ML 2 contain hexacoordinated Ti; in M 2 L the coordination number is probably five. The dynamics of exchange of the lactam between the ML 2 complexes and the uncomplexed form have been characterized and structures are proposed for the four complexes.

NMR study of complex formation between TiCl4 and N-Methylated lactams with 7- and 9-membered rings

Abstract By analysis of 1 H- and 13 C-NMR spectra it has been found that in 1,1,2,2-tetrachloroethane- d 2 and CDCl 3 solutions, the lactams (L) 1-methyl-1-azacycloheptca-2-one and 1-methyl-1-azacyclonona-2-one form with TiCl 4 (M) at mole ratios [L]: [M] > 2 two types of complexes of composition ML 2 , which differ in the geometrical arrangement of the ligands. The thermodynamic parameters of the exchange of lactams between the two complexes and the uncomplexed state were determined from the temperature dependence of 1 H-NMR line shapes and found to be independent of the lactam ring size.

NMR and raman spectroscopic study of complex formation between TiCl4 and N-methylated lactams with 11- and 13-membered rings

Abstract Complex formation between N -methylated lactams (L) with 11- and 13-membered rings which in the liquid state assume both the cis and the trans structures of the amide bond, and TiCl 4 , (M) in 1,1,2,2-tetrachloroethane and CDCl 3 solutions has been studied by analysis of 1 H and 13 C-NMR and Raman spectra. The composition and structure of the complexes as well as the effect of TiCl 4 , on the cis — trans isomerization equilibrium have been determined. As for the lower cis lactams, it was found that at molar ratios [L]:[M] > 2, the lactams with the 11- and 13-membered rings form complexes of composition ML 2 . The free energies of activation for the exchange processes in these systems were estimated from the temperature dependence of 1 H-NMR spectra and it was found that the barrier to rotation about the amide bond is increased by complex formation.