... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO)... more ... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO) and N,N-dimethyl-acetamide C3H9NO ... Pharmacie de l'Université Paris Descartes, 4, avenue de l'observatoire, 75006 Paris, France e-mail: beatrice.nicolai@parisdescartes ...
ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have ... more ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have been measured and assigned to separate CH3 groups on the basis of the low-temperature crystal structure. Ab initio and molecular-mechanics calculations have been applied to account for the anti-parallel orientation of the two CH3 groups in the crystal. For the isolated molecule the rotational potential of one group depends on the orientation of the other.
Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the t... more Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the tunnelling splittings to the two crystallographically-inequivalent methyl groups in 2,6-dimethylpyrazine (C6N2H8) at 2 K. Their antiparallel conformation found by crystallography and their respective rotational barriers are reproduced by a combination of ab-initio and molecular mechanics calculations. These results are used for a better understanding of the methyl groups dynamics.
The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delt... more The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delta(fus)H(I) = 36.6 +/- 0.9 kJ mol(-1)) recrystallizes into another phase, Phase II, that melts at T(fusII) = 373.8 +/- 0.2 K (Delta(fus)H(II) = 28.8 +/- 1.0 kJ mol(-1)). The transformation of Phase II into Phase I is found to be exothermic upon heating either as a direct process at 363 K or through a melting-recrystallization process (II --> liquid --> I). The melting curves, obtained from differential thermal analyses at various pressures ranging from 0 to 85 MPa, diverge as the pressure increases ((dP/dT)(fusI) = 2.54 +/- 0.07 MPa K(-1), (dP/dT)(fusII) = 5.14 +/- 0.85 MPa K(-1)). A topological P-T diagram with no stable phase region for Phase II, and similar to the 4th case of the P-T state diagrams formerly published by Bakhuis Roozeboom, is drawn, thus illustrating the overall monotropic behavior of Phase II.
La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupemen... more La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupements methyles donnent des informations tres precises sur le potentiel rotationnel local. La presence de plusieurs transitions d'effet tunnel pour le meme systeme reste un phenomene rare qui peut etre interprete en termes de rotateurs inequivalents ou de couplages. Il apparait que l'interpretation de ces donnees experimentales necessite la connaissance precise de la structure cristalline a tres basse temperature et si possible la distribution des protons. L'objectif de cette these est d'interpreter ces mesures experimentales en attribuant les transitions observees. Une fois ce travail experimental acheve, il reste a comprendre les relations entre structure et dynamique. Les modelisations utilisant diverses methodes de calcul ont permis de relier les dynamiques observees a des parametres physico-chimiques. Ces differentes methodes de calcul du potentiel rotationnel sont comparees et leurs fiabilites et limites sont discutees.
ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKa... more ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKay, M P Zorzano, (World Scientific, Publishing Co., Inc) p68 (2003) ISBN 981-283-296-8
1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensat... more 1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensation of propane-1,3-diamine with a mixture of (1H-1,2,4-triazol-1-yl)methanol and formaldehyde. The 1H- and 13C-NMR spectroscopic data of this ligand have been fully assigned and are consistent with the molecular structure. The crystalline structure of the compound was fully determined by single crystal X-ray diffraction at 150K and at room temperature, together with the isobaric thermal expansion. Finally, during the first heating, DSC measurements showed no phase transition up to the melting temperature at 385.1 K (111.9°C).
... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO)... more ... Organic sol-vents such as N,N-dimethylformamide C3H7NO (DMF), dimethylsulfoxide C2H6SO (DMSO) and N,N-dimethyl-acetamide C3H9NO ... Pharmacie de l'Université Paris Descartes, 4, avenue de l'observatoire, 75006 Paris, France e-mail: beatrice.nicolai@parisdescartes ...
ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have ... more ABSTRACT The two methyl tunnelling-frequencies of a single crystal of 2,6 dimethyl pyrazine have been measured and assigned to separate CH3 groups on the basis of the low-temperature crystal structure. Ab initio and molecular-mechanics calculations have been applied to account for the anti-parallel orientation of the two CH3 groups in the crystal. For the isolated molecule the rotational potential of one group depends on the orientation of the other.
Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the t... more Inelastic neutron scattering (INS) on an oriented single-crystal is used to assign directly the tunnelling splittings to the two crystallographically-inequivalent methyl groups in 2,6-dimethylpyrazine (C6N2H8) at 2 K. Their antiparallel conformation found by crystallography and their respective rotational barriers are reproduced by a combination of ab-initio and molecular mechanics calculations. These results are used for a better understanding of the methyl groups dynamics.
The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delt... more The melt from the usual monoclinic phase (Phase I) of biclotymol (T(fusI) = 400.5 +/- 1.0 K, Delta(fus)H(I) = 36.6 +/- 0.9 kJ mol(-1)) recrystallizes into another phase, Phase II, that melts at T(fusII) = 373.8 +/- 0.2 K (Delta(fus)H(II) = 28.8 +/- 1.0 kJ mol(-1)). The transformation of Phase II into Phase I is found to be exothermic upon heating either as a direct process at 363 K or through a melting-recrystallization process (II --> liquid --> I). The melting curves, obtained from differential thermal analyses at various pressures ranging from 0 to 85 MPa, diverge as the pressure increases ((dP/dT)(fusI) = 2.54 +/- 0.07 MPa K(-1), (dP/dT)(fusII) = 5.14 +/- 0.85 MPa K(-1)). A topological P-T diagram with no stable phase region for Phase II, and similar to the 4th case of the P-T state diagrams formerly published by Bakhuis Roozeboom, is drawn, thus illustrating the overall monotropic behavior of Phase II.
La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupemen... more La mesure des transitions d'effet tunnel par diffusion inelastique des neutrons des groupements methyles donnent des informations tres precises sur le potentiel rotationnel local. La presence de plusieurs transitions d'effet tunnel pour le meme systeme reste un phenomene rare qui peut etre interprete en termes de rotateurs inequivalents ou de couplages. Il apparait que l'interpretation de ces donnees experimentales necessite la connaissance precise de la structure cristalline a tres basse temperature et si possible la distribution des protons. L'objectif de cette these est d'interpreter ces mesures experimentales en attribuant les transitions observees. Une fois ce travail experimental acheve, il reste a comprendre les relations entre structure et dynamique. Les modelisations utilisant diverses methodes de calcul ont permis de relier les dynamiques observees a des parametres physico-chimiques. Ces differentes methodes de calcul du potentiel rotationnel sont comparees et leurs fiabilites et limites sont discutees.
ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKa... more ABSTRACT in Localization & Energy Transfer in Nonlinear Systems, Eds L Vazquez, R S MacKay, M P Zorzano, (World Scientific, Publishing Co., Inc) p68 (2003) ISBN 981-283-296-8
1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensat... more 1,3-bis((1H-1,2,4-triazol-1-yl)methyl)hexahydropyrimidine were readily prepared by cyclocondensation of propane-1,3-diamine with a mixture of (1H-1,2,4-triazol-1-yl)methanol and formaldehyde. The 1H- and 13C-NMR spectroscopic data of this ligand have been fully assigned and are consistent with the molecular structure. The crystalline structure of the compound was fully determined by single crystal X-ray diffraction at 150K and at room temperature, together with the isobaric thermal expansion. Finally, during the first heating, DSC measurements showed no phase transition up to the melting temperature at 385.1 K (111.9°C).
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