Calculations of the molecular interactions in 1,3-dibromo-2,4,6-trimethyl-benzene: which methyl groups are quasi-free rotors in the crystal?
| Autor: | Fanni Juranyi, Jean Meinnel, Abdou Boucekkine, Colin Carlile, Mourad Mimouni, Soria Zeroual, Mohammed Sadok Mahboub, Imad Hamadneh, Ali Boudjada |
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| Přispěvatelé: | Institut des Sciences Chimiques de Rennes (ISCR), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université d'El-Oued, Paul Scherrer Institute (PSI), Uppsala University, The University of Jordan (JU), Université Mentouri Constantine [Algérie] (UMC), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Ecole Nationale Supérieure de Chimie de Rennes (ENSCR)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Université frères Mentouri Constantine I (UMC) |
| Jazyk: | angličtina |
| Rok vydání: | 2021 |
| Předmět: |
Materials science
010304 chemical physics Spin states General Physics and Astronomy 010402 general chemistry 01 natural sciences Molecular physics Inelastic neutron scattering 0104 chemical sciences Crystal [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry Delocalized electron symbols.namesake 0103 physical sciences symbols [CHIM.CRIS]Chemical Sciences/Cristallography Molecule [CHIM]Chemical Sciences Density functional theory Physical and Theoretical Chemistry van der Waals force Monoclinic crystal system |
| Zdroj: | Physical Chemistry Chemical Physics Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2021, ⟨10.1039/d1cp02581c⟩ Physical Chemistry Chemical Physics, 2021, 23 (37), pp.21272-21285. ⟨10.1039/d1cp02581c⟩ |
| ISSN: | 1463-9076 1463-9084 |
| DOI: | 10.1039/d1cp02581c⟩ |
| Popis: | International audience; Dibromomesitylene (DBMH) is one of the few molecules in which a methyl group is a quasi-free rotor in the crystal state. Density functional theory calculations - using the Born-Oppenheimer approximation (BOa) - indicate that in isolated DBMH, Me4 and Me6 are highly hindered in a 3-fold potential V-3 > 55 meV while Me2 symmetrically located between two Br atoms has a small 6-fold rotation hindering potential: V-6 similar to 8 meV. Inelastic neutron scattering studies have shown that this is also true in the crystal, the Me2 tunneling gap being 390 mu eV at 4.2 K and V-6 similar to 18 meV. In the monoclinic DBMH crystal, molecules are packed in an anti-ferroelectric manner along the oblique a axis, favoring strong van der Waals interactions, while in the corrugated bc planes each molecule has a quasi hexagonal environment and weaker interactions. This results in the nearby environment of Me2 only being composed of hydrogen atoms. This explains why the Me2 rotation barrier remains small in the crystal and mainly 6-fold. Using the same potentials in the Schrodinger equation for a -CD3 rotor has allowed predicting a tunneling gap of 69 mu eV for deuterated Me2 in very good agreement with inelastic neutron scattering measurements. Therefore, because of a rare and unexpected local symmetry in the crystal, the Me2 rotation barrier remains small and 6-fold and hydrogen nuclei are highly delocalized and not relevant to the Born-Oppenheimer approximation. This and the neglect of spin states explain the failure of density functional theory calculations for finding the rotation energy levels of Me2. |
| Databáze: | OpenAIRE |
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