Structure of trihalogenomesitylenes and tunneling of the methyl groups protons
Identifieur interne : 001A51 ( Istex/Corpus ); précédent : 001A50; suivant : 001A52Structure of trihalogenomesitylenes and tunneling of the methyl groups protons
Auteurs : J. Meinnel ; M. Mani ; A. Cousson ; F. Boudjada ; W. Paulus ; M. JohnsonSource :
- Chemical Physics [ 0301-0104 ] ; 2000.
Abstract
The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P1 and Z=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C3h symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the Car–Car–Cme angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.
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DOI: 10.1016/S0301-0104(00)00242-1
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Cousson</name><affiliation><mods:affiliation>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</mods:affiliation></affiliation></author><author><name sortKey="Boudjada, F" sort="Boudjada, F" uniqKey="Boudjada F" first="F." last="Boudjada">F. Boudjada</name><affiliation><mods:affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</mods:affiliation></affiliation></author><author><name sortKey="Paulus, W" sort="Paulus, W" uniqKey="Paulus W" first="W." last="Paulus">W. Paulus</name><affiliation><mods:affiliation>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</mods:affiliation></affiliation></author><author><name sortKey="Johnson, M" sort="Johnson, M" uniqKey="Johnson M" first="M." last="Johnson">M. Johnson</name><affiliation><mods:affiliation>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</mods:affiliation></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">ISTEX</idno><idno type="RBID">ISTEX:ABE834553FC3872CDD0DDC05FD0DD91C964A9229</idno><date when="2000" year="2000">2000</date><idno type="doi">10.1016/S0301-0104(00)00242-1</idno><idno type="url">https://api.istex.fr/document/ABE834553FC3872CDD0DDC05FD0DD91C964A9229/fulltext/pdf</idno><idno type="wicri:Area/Istex/Corpus">001A51</idno><idno type="wicri:explorRef" wicri:stream="Istex" wicri:step="Corpus" wicri:corpus="ISTEX">001A51</idno></publicationStmt><sourceDesc><biblStruct><analytic><title level="a">Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><author><name sortKey="Meinnel, J" sort="Meinnel, J" uniqKey="Meinnel J" first="J." last="Meinnel">J. Meinnel</name><affiliation><mods:affiliation>E-mail: meinnel.j@wanadoo.fr</mods:affiliation></affiliation><affiliation><mods:affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</mods:affiliation></affiliation></author><author><name sortKey="Mani, M" sort="Mani, M" uniqKey="Mani M" first="M." last="Mani">M. Mani</name><affiliation><mods:affiliation>Département de Physique de la Faculté des Sciences, Université Chouaib Doukkali, El-Jadida, Morocco</mods:affiliation></affiliation></author><author><name sortKey="Cousson, A" sort="Cousson, A" uniqKey="Cousson A" first="A." last="Cousson">A. Cousson</name><affiliation><mods:affiliation>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</mods:affiliation></affiliation></author><author><name sortKey="Boudjada, F" sort="Boudjada, F" uniqKey="Boudjada F" first="F." last="Boudjada">F. Boudjada</name><affiliation><mods:affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</mods:affiliation></affiliation></author><author><name sortKey="Paulus, W" sort="Paulus, W" uniqKey="Paulus W" first="W." last="Paulus">W. Paulus</name><affiliation><mods:affiliation>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</mods:affiliation></affiliation></author><author><name sortKey="Johnson, M" sort="Johnson, M" uniqKey="Johnson M" first="M." last="Johnson">M. Johnson</name><affiliation><mods:affiliation>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</mods:affiliation></affiliation></author></analytic><monogr></monogr><series><title level="j">Chemical Physics</title><title level="j" type="abbrev">CHEMPH</title><idno type="ISSN">0301-0104</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="2000">2000</date><biblScope unit="volume">261</biblScope><biblScope unit="issue">1–2</biblScope><biblScope unit="page" from="165">165</biblScope><biblScope unit="page" to="187">187</biblScope></imprint><idno type="ISSN">0301-0104</idno></series><idno type="istex">ABE834553FC3872CDD0DDC05FD0DD91C964A9229</idno><idno type="DOI">10.1016/S0301-0104(00)00242-1</idno><idno type="PII">S0301-0104(00)00242-1</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0301-0104</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P1 and Z=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C3h symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the Car–Car–Cme angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.</div></front></TEI><istex><corpusName>elsevier</corpusName><author><json:item><name>J. Meinnel</name><affiliations><json:string>E-mail: meinnel.j@wanadoo.fr</json:string><json:string>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</json:string></affiliations></json:item><json:item><name>M. Mani</name><affiliations><json:string>Département de Physique de la Faculté des Sciences, Université Chouaib Doukkali, El-Jadida, Morocco</json:string></affiliations></json:item><json:item><name>A. Cousson</name><affiliations><json:string>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</json:string></affiliations></json:item><json:item><name>F. Boudjada</name><affiliations><json:string>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</json:string></affiliations></json:item><json:item><name>W. Paulus</name><affiliations><json:string>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</json:string></affiliations></json:item><json:item><name>M. Johnson</name><affiliations><json:string>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</json:string></affiliations></json:item></author><language><json:string>eng</json:string></language><originalGenre><json:string>Full-length article</json:string></originalGenre><abstract>The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P1 and Z=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C3h symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the Car–Car–Cme angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.</abstract><qualityIndicators><score>8</score><pdfVersion>1.2</pdfVersion><pdfPageSize>544 x 743 pts</pdfPageSize><refBibsNative>true</refBibsNative><keywordCount>0</keywordCount><abstractCharCount>1627</abstractCharCount><pdfWordCount>10090</pdfWordCount><pdfCharCount>61664</pdfCharCount><pdfPageCount>23</pdfPageCount><abstractWordCount>251</abstractWordCount></qualityIndicators><title>Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><pii><json:string>S0301-0104(00)00242-1</json:string></pii><genre><json:string>research-article</json:string></genre><host><volume>261</volume><pii><json:string>S0301-0104(00)X0144-9</json:string></pii><pages><last>187</last><first>165</first></pages><issn><json:string>0301-0104</json:string></issn><issue>1–2</issue><genre><json:string>journal</json:string></genre><language><json:string>unknown</json:string></language><title>Chemical Physics</title><publicationDate>2000</publicationDate></host><categories><wos><json:string>PHYSICS, ATOMIC, MOLECULAR & CHEMICAL</json:string><json:string>CHEMISTRY, PHYSICAL</json:string></wos></categories><publicationDate>2000</publicationDate><copyrightDate>2000</copyrightDate><doi><json:string>10.1016/S0301-0104(00)00242-1</json:string></doi><id>ABE834553FC3872CDD0DDC05FD0DD91C964A9229</id><score>0.028403461</score><fulltext><json:item><original>true</original><mimetype>application/pdf</mimetype><extension>pdf</extension><uri>https://api.istex.fr/document/ABE834553FC3872CDD0DDC05FD0DD91C964A9229/fulltext/pdf</uri></json:item><json:item><original>false</original><mimetype>application/zip</mimetype><extension>zip</extension><uri>https://api.istex.fr/document/ABE834553FC3872CDD0DDC05FD0DD91C964A9229/fulltext/zip</uri></json:item><istex:fulltextTEI uri="https://api.istex.fr/document/ABE834553FC3872CDD0DDC05FD0DD91C964A9229/fulltext/tei"><teiHeader><fileDesc><titleStmt><title level="a">Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><title level="a" type="sub">II. Protonated tribromomesitylene</title></titleStmt><publicationStmt><authority>ISTEX</authority><publisher>ELSEVIER</publisher><availability><p>©2000 Elsevier Science B.V.</p></availability><date>2000</date></publicationStmt><notesStmt><note type="content">Fig. 1: Orthogonal projection on to the plane perpendicular to the (100) plane which contains the a axis.</note><note type="content">Fig. 2: Orthogonal projection onto the (100) plane.</note><note type="content">Fig. 3: (a) Mean conformation from neutron diffraction at 14 K (solid) and (b) conformation calculated with mopac–pm3 (isolated molecule).</note><note type="content">Fig. 4: Variation of the potential energy for a rotation of a probe molecule around an axis perpendicular to the plane of the benzene ring: (exp, −6) and Coulomb contributions.</note><note type="content">Fig. 5: Proton probability density for each methyl group: (a) methyl 7, (b) methyl 8, and (c) methyl 9.</note><note type="content">Fig. 6: Graphs of the tunneling splitting as a function of the hindering potential, for various components V3 and V6 with q=V3/(V3+V6) and two values of the phase φ6 (0°,180°). For the three tunnel frequencies of TBM9H, torsional transitions E01 are indicated by grey squares in the region 5–10 meV and transitions E02 by grey lines in the region 16–22 meV.</note><note type="content">Fig. 7: Tunneling excitations of the three methyl groups of TBM9H recorded on the backscattering spectrometer IN10c (KCl (2,0,0) monochromator.</note><note type="content">Fig. 8: Variation of the intensity of the tunneling excitations versus the modulus Q of the impulse vector (TBM9H tunneling energies in μeV: A=48.1, B=13.6, and C=24.5).</note><note type="content">Fig. 9: Proton probability density for the three methyl groups in TBM9H. The open squares correspond to the result of neutron diffraction, the curves are calculated from the wave functions of Table 6.</note><note type="content">Fig. 10: Rotational hindering potential of methyl groups determined by mopac-am1.</note><note type="content">Fig. 11: Protons probability density for the three methyl groups in TBM9H: experimental Fourier difference maps at 295 K: (a) Methyl 7, (b) Methyl 8, and (c) Methyl 9.</note><note type="content">Table 1: Atomic positions given in fraction of the cell parameters and isotropic thermal motion factors U(iso) for TBM9H at 14 K</note><note type="content">Table 2: Individual isotropic and anisotropic thermal motion factors at 14 K</note><note type="content">Table 3: Refined bond lengths at 14 K, mean value for equivalent bonds and results of PM3 calculations</note><note type="content">Table 4: Refined bond angles at 14 K, mean value for equivalent angles and results of PM3 calculations</note><note type="content">Table 5: Coefficients of the Buckingham potential used to calculate the lattice modes of TBM9H</note><note type="content">Table 6: Hindering potentials, tunneling and torsional excitations and resulting wave functions for the three methyl groups of TBM9H</note><note type="content">Table 7: Total binding energies, Vb, between atomic cores and valence electrons among mopac–am1 and pm3</note><note type="content">Table 8: Atomic positions (fractions of the cell parameters) and isotropic thermal motion factors Uiso for TBM9H at 295 K</note><note type="content">Table 9: Individual anisotropic thermal motion factors Uij at 295 K</note><note type="content">Table 10: Refined bond lengths at 295 K, mean values at 295 and 14 K for equivalent bonds</note><note type="content">Table 11: Bond angles (°) at 295 K</note></notesStmt><sourceDesc><biblStruct type="inbook"><analytic><title level="a">Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><title level="a" type="sub">II. Protonated tribromomesitylene</title><author xml:id="author-1"><persName><forename type="first">J.</forename><surname>Meinnel</surname></persName><email>meinnel.j@wanadoo.fr</email><note type="correspondence"><p>Corresponding author</p></note><affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</affiliation></author><author xml:id="author-2"><persName><forename type="first">M.</forename><surname>Mani</surname></persName><affiliation>Département de Physique de la Faculté des Sciences, Université Chouaib Doukkali, El-Jadida, Morocco</affiliation></author><author xml:id="author-3"><persName><forename type="first">A.</forename><surname>Cousson</surname></persName><affiliation>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</affiliation></author><author xml:id="author-4"><persName><forename type="first">F.</forename><surname>Boudjada</surname></persName><affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</affiliation></author><author xml:id="author-5"><persName><forename type="first">W.</forename><surname>Paulus</surname></persName><affiliation>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</affiliation></author><author xml:id="author-6"><persName><forename type="first">M.</forename><surname>Johnson</surname></persName><affiliation>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</affiliation></author></analytic><monogr><title level="j">Chemical Physics</title><title level="j" type="abbrev">CHEMPH</title><idno type="pISSN">0301-0104</idno><idno type="PII">S0301-0104(00)X0144-9</idno><imprint><publisher>ELSEVIER</publisher><date type="published" when="2000"></date><biblScope unit="volume">261</biblScope><biblScope unit="issue">1–2</biblScope><biblScope unit="page" from="165">165</biblScope><biblScope unit="page" to="187">187</biblScope></imprint></monogr><idno type="istex">ABE834553FC3872CDD0DDC05FD0DD91C964A9229</idno><idno type="DOI">10.1016/S0301-0104(00)00242-1</idno><idno type="PII">S0301-0104(00)00242-1</idno></biblStruct></sourceDesc></fileDesc><profileDesc><creation><date>2000</date></creation><langUsage><language ident="en">en</language></langUsage><abstract xml:lang="en"><p>The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P1 and Z=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C3h symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the Car–Car–Cme angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.</p></abstract></profileDesc><revisionDesc><change when="2000">Published</change></revisionDesc></teiHeader></istex:fulltextTEI><json:item><original>false</original><mimetype>text/plain</mimetype><extension>txt</extension><uri>https://api.istex.fr/document/ABE834553FC3872CDD0DDC05FD0DD91C964A9229/fulltext/txt</uri></json:item></fulltext><metadata><istex:metadataXml wicri:clean="Elsevier, elements deleted: ce:floats; body; tail"><istex:xmlDeclaration>version="1.0" encoding="utf-8"</istex:xmlDeclaration><istex:docType PUBLIC="-//ES//DTD journal article DTD version 4.5.2//EN//XML" URI="art452.dtd" name="istex:docType"><istex:entity SYSTEM="gr1" NDATA="IMAGE" name="gr1"></istex:entity><istex:entity SYSTEM="gr2" NDATA="IMAGE" name="gr2"></istex:entity><istex:entity SYSTEM="gr3" NDATA="IMAGE" name="gr3"></istex:entity><istex:entity SYSTEM="gr4" NDATA="IMAGE" name="gr4"></istex:entity><istex:entity SYSTEM="gr5" NDATA="IMAGE" name="gr5"></istex:entity><istex:entity SYSTEM="gr6" NDATA="IMAGE" name="gr6"></istex:entity><istex:entity SYSTEM="gr7" NDATA="IMAGE" name="gr7"></istex:entity><istex:entity SYSTEM="gr8" NDATA="IMAGE" name="gr8"></istex:entity><istex:entity SYSTEM="gr9" NDATA="IMAGE" name="gr9"></istex:entity><istex:entity SYSTEM="gr10" NDATA="IMAGE" name="gr10"></istex:entity><istex:entity SYSTEM="gr11" NDATA="IMAGE" name="gr11"></istex:entity></istex:docType><istex:document><converted-article version="4.5.2" docsubtype="fla"><item-info><jid>CHEMPH</jid><aid>4084</aid><ce:pii>S0301-0104(00)00242-1</ce:pii><ce:doi>10.1016/S0301-0104(00)00242-1</ce:doi><ce:copyright type="full-transfer" year="2000">Elsevier Science B.V.</ce:copyright></item-info><head><ce:title>Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</ce:title><ce:subtitle>II. Protonated tribromomesitylene</ce:subtitle><ce:author-group><ce:author><ce:given-name>J.</ce:given-name><ce:surname>Meinnel</ce:surname><ce:cross-ref refid="AFF1"><ce:sup>a</ce:sup></ce:cross-ref><ce:cross-ref refid="CORR1">*</ce:cross-ref><ce:e-address>meinnel.j@wanadoo.fr</ce:e-address></ce:author><ce:author><ce:given-name>M.</ce:given-name><ce:surname>Mani</ce:surname><ce:cross-ref refid="AFF2"><ce:sup>b</ce:sup></ce:cross-ref></ce:author><ce:author><ce:given-name>A.</ce:given-name><ce:surname>Cousson</ce:surname><ce:cross-ref refid="AFF3"><ce:sup>c</ce:sup></ce:cross-ref></ce:author><ce:author><ce:given-name>F.</ce:given-name><ce:surname>Boudjada</ce:surname><ce:cross-ref refid="AFF1"><ce:sup>a</ce:sup></ce:cross-ref></ce:author><ce:author><ce:given-name>W.</ce:given-name><ce:surname>Paulus</ce:surname><ce:cross-ref refid="AFF4"><ce:sup>d</ce:sup></ce:cross-ref></ce:author><ce:author><ce:given-name>M.</ce:given-name><ce:surname>Johnson</ce:surname><ce:cross-ref refid="AFF5"><ce:sup>e</ce:sup></ce:cross-ref></ce:author><ce:affiliation id="AFF1"><ce:label>a</ce:label><ce:textfn>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</ce:textfn></ce:affiliation><ce:affiliation id="AFF2"><ce:label>b</ce:label><ce:textfn>Département de Physique de la Faculté des Sciences, Université Chouaib Doukkali, El-Jadida, Morocco</ce:textfn></ce:affiliation><ce:affiliation id="AFF3"><ce:label>c</ce:label><ce:textfn>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</ce:textfn></ce:affiliation><ce:affiliation id="AFF4"><ce:label>d</ce:label><ce:textfn>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</ce:textfn></ce:affiliation><ce:affiliation id="AFF5"><ce:label>e</ce:label><ce:textfn>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</ce:textfn></ce:affiliation><ce:correspondence id="CORR1"><ce:label>*</ce:label><ce:text>Corresponding author</ce:text></ce:correspondence></ce:author-group><ce:date-received day="4" month="7" year="2000"></ce:date-received><ce:abstract><ce:section-title>Abstract</ce:section-title><ce:abstract-sec><ce:simple-para>The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P<math altimg="si18.gif"><ovl type="bar">1</ovl></math> and <ce:italic>Z</ce:italic>=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C<ce:inf>3h</ce:inf> symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the C<ce:inf>ar</ce:inf>–C<ce:inf>ar</ce:inf>–C<ce:inf>me</ce:inf> angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.</ce:simple-para></ce:abstract-sec></ce:abstract></head></converted-article></istex:document></istex:metadataXml><mods version="3.6"><titleInfo><title>Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><subTitle>II. Protonated tribromomesitylene</subTitle></titleInfo><titleInfo type="alternative" contentType="CDATA"><title>Structure of trihalogenomesitylenes and tunneling of the methyl groups protons</title><subTitle>II. Protonated tribromomesitylene</subTitle></titleInfo><name type="personal"><namePart type="given">J.</namePart><namePart type="family">Meinnel</namePart><affiliation>E-mail: meinnel.j@wanadoo.fr</affiliation><affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</affiliation><description>Corresponding author</description><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Mani</namePart><affiliation>Département de Physique de la Faculté des Sciences, Université Chouaib Doukkali, El-Jadida, Morocco</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">A.</namePart><namePart type="family">Cousson</namePart><affiliation>Laboratoire Léon Brillouin, C.E. de Saclay, F-91191, Gif-sur-Yvette, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">F.</namePart><namePart type="family">Boudjada</namePart><affiliation>Groupe Matière Condensée et Matériaux, Université de Rennes 1, UMR CRNS 6626, F-35042 Rennes, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">W.</namePart><namePart type="family">Paulus</namePart><affiliation>Laboratoire de Chimie du Solide et Inorganique Moléculaire, UMR CRNS-6511, Université de Rennes 1, F-35042 Rennes, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><name type="personal"><namePart type="given">M.</namePart><namePart type="family">Johnson</namePart><affiliation>Institut Laue-Langevin, Avenue des Martyrs, F-38042 Grenoble, France</affiliation><role><roleTerm type="text">author</roleTerm></role></name><typeOfResource>text</typeOfResource><genre type="research-article" displayLabel="Full-length article"></genre><originInfo><publisher>ELSEVIER</publisher><dateIssued encoding="w3cdtf">2000</dateIssued><copyrightDate encoding="w3cdtf">2000</copyrightDate></originInfo><language><languageTerm type="code" authority="iso639-2b">eng</languageTerm><languageTerm type="code" authority="rfc3066">en</languageTerm></language><physicalDescription><internetMediaType>text/html</internetMediaType></physicalDescription><abstract lang="en">The crystal structure of protonated 1,3,5-tribromo-2,4,6-trimethyl benzene is studied at 295 and 14 K by single-crystal neutron diffraction. In this temperature range, the structure is always triclinic: P1 and Z=2. All atoms are in the plane of the aromatic ring except two staggered protons of each methyl group. Consequently, deviation from C3h symmetry is negligible for the whole molecule. In the aromatic ring, a significant shortening of the C–C bond facing the eclipsed C–H bond is observed, while the Car–Car–Cme angle is increased to 123.3°. The apparent conformation of the proton density in the methyl groups varies drastically as a function of temperature. At 14 K, the proton density shows three maxima for each methyl group, located on a circle of radius 1.006 Å. Solving the Schrödinger equation, we have found the potentials compatible with the excitations measured in the incoherent inelastic neutron scattering spectrum. The eigenvectors corresponding to the two lower states allowed us to calculate a proton density very close to that measured by neutron diffraction at 14 K. These results establish a strong correlation between coherent and incoherent neutron scattering, for methyl groups treated as uniaxial rotors. However, at 295 K, four maxima of proton density were found, which were attributed to a complex coupling between the methyl rotor and various motions of the molecule. Therefore, the anisotropic spreading of proton density at low temperature is basically of quantum nature while, at higher temperatures, the apparent deformation of the methyl group is the result of complex thermal motions.</abstract><note type="content">Fig. 1: Orthogonal projection on to the plane perpendicular to the (100) plane which contains the a axis.</note><note type="content">Fig. 2: Orthogonal projection onto the (100) plane.</note><note type="content">Fig. 3: (a) Mean conformation from neutron diffraction at 14 K (solid) and (b) conformation calculated with mopac–pm3 (isolated molecule).</note><note type="content">Fig. 4: Variation of the potential energy for a rotation of a probe molecule around an axis perpendicular to the plane of the benzene ring: (exp, −6) and Coulomb contributions.</note><note type="content">Fig. 5: Proton probability density for each methyl group: (a) methyl 7, (b) methyl 8, and (c) methyl 9.</note><note type="content">Fig. 6: Graphs of the tunneling splitting as a function of the hindering potential, for various components V3 and V6 with q=V3/(V3+V6) and two values of the phase φ6 (0°,180°). For the three tunnel frequencies of TBM9H, torsional transitions E01 are indicated by grey squares in the region 5–10 meV and transitions E02 by grey lines in the region 16–22 meV.</note><note type="content">Fig. 7: Tunneling excitations of the three methyl groups of TBM9H recorded on the backscattering spectrometer IN10c (KCl (2,0,0) monochromator.</note><note type="content">Fig. 8: Variation of the intensity of the tunneling excitations versus the modulus Q of the impulse vector (TBM9H tunneling energies in μeV: A=48.1, B=13.6, and C=24.5).</note><note type="content">Fig. 9: Proton probability density for the three methyl groups in TBM9H. The open squares correspond to the result of neutron diffraction, the curves are calculated from the wave functions of Table 6.</note><note type="content">Fig. 10: Rotational hindering potential of methyl groups determined by mopac-am1.</note><note type="content">Fig. 11: Protons probability density for the three methyl groups in TBM9H: experimental Fourier difference maps at 295 K: (a) Methyl 7, (b) Methyl 8, and (c) Methyl 9.</note><note type="content">Table 1: Atomic positions given in fraction of the cell parameters and isotropic thermal motion factors U(iso) for TBM9H at 14 K</note><note type="content">Table 2: Individual isotropic and anisotropic thermal motion factors at 14 K</note><note type="content">Table 3: Refined bond lengths at 14 K, mean value for equivalent bonds and results of PM3 calculations</note><note type="content">Table 4: Refined bond angles at 14 K, mean value for equivalent angles and results of PM3 calculations</note><note type="content">Table 5: Coefficients of the Buckingham potential used to calculate the lattice modes of TBM9H</note><note type="content">Table 6: Hindering potentials, tunneling and torsional excitations and resulting wave functions for the three methyl groups of TBM9H</note><note type="content">Table 7: Total binding energies, Vb, between atomic cores and valence electrons among mopac–am1 and pm3</note><note type="content">Table 8: Atomic positions (fractions of the cell parameters) and isotropic thermal motion factors Uiso for TBM9H at 295 K</note><note type="content">Table 9: Individual anisotropic thermal motion factors Uij at 295 K</note><note type="content">Table 10: Refined bond lengths at 295 K, mean values at 295 and 14 K for equivalent bonds</note><note type="content">Table 11: Bond angles (°) at 295 K</note><relatedItem type="host"><titleInfo><title>Chemical Physics</title></titleInfo><titleInfo type="abbreviated"><title>CHEMPH</title></titleInfo><genre type="journal">journal</genre><originInfo><dateIssued encoding="w3cdtf">20001101</dateIssued></originInfo><identifier type="ISSN">0301-0104</identifier><identifier type="PII">S0301-0104(00)X0144-9</identifier><part><date>20001101</date><detail type="volume"><number>261</number><caption>vol.</caption></detail><detail type="issue"><number>1–2</number><caption>no.</caption></detail><extent unit="issue pages"><start>1</start><end>274</end></extent><extent unit="pages"><start>165</start><end>187</end></extent></part></relatedItem><identifier type="istex">ABE834553FC3872CDD0DDC05FD0DD91C964A9229</identifier><identifier type="DOI">10.1016/S0301-0104(00)00242-1</identifier><identifier type="PII">S0301-0104(00)00242-1</identifier><accessCondition type="use and reproduction" contentType="copyright">©2000 Elsevier Science B.V.</accessCondition><recordInfo><recordContentSource>ELSEVIER</recordContentSource><recordOrigin>Elsevier Science B.V., ©2000</recordOrigin></recordInfo></mods></metadata><serie></serie></istex></record>Pour manipuler ce document sous Unix (Dilib)
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