Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane
Cyclohexane is an extremely flexible molecule that oscillates, at room temperature, between two clearly distinct and extreme conformations that cannot be distinguished at room temperature; so much so that the NMR spectrum is a single line that includes all 12 protons be they axial or equatorial. Thi...
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todo:paper_10895639_v115_n33_p9207_Bain2023-10-03T16:04:43Z Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane Bain, A.D. Baron, M. Burger, S.K. Kowalewski, V.J. Rodríguez, M.B. Calculation methods Carbon atoms Centrosymmetric Crystalline solids Cyclohexane ring Different solvents Enthalpy of activation Equatorial positions Field intensity Flexible molecules Interconversions Low magnetic fields Low temperatures NMR spectrum Proton NMR Reaction coordinates Room temperature Six-membered rings Small molecules Structure and dynamics Vapor Phase Variable temperature X-ray diffraction studies Behavioral research Bromine Conformations Magnetic fields Molecules Nuclear magnetic resonance Nuclear magnetic resonance spectroscopy Protons Quantum chemistry X ray diffraction Cyclohexane Cyclohexane is an extremely flexible molecule that oscillates, at room temperature, between two clearly distinct and extreme conformations that cannot be distinguished at room temperature; so much so that the NMR spectrum is a single line that includes all 12 protons be they axial or equatorial. This raises the interesting question as to what happens when there are equal substituents at the 1 and 4 carbon atoms of the ring. Therefore substitution in the 1,4-positions in the cyclohexane ring has been the subject of considerable interest because some form of interconversion between extreme conformations could lead to the existence of a rather unusual behavior. To study this problem, the interconversion in (di- or tetra-1,4)-substituted six-membered cyclohexane-type rings, trans-1,4-dibromo-1,4-dicyanocyclohexane, was found to be a particularly suitable candidate. Although X-ray diffraction studies on the crystalline solid found the molecule to be centrosymmetric, it still shows a significant dipole moment μ in solution, as determined with a procedure that leads to the vapor phase values of μ. Furthermore, the low magnetic field proton NMR spectrum at ambient temperature appears as a single line, a situation that changes with increasing field intensity and different solvents. Both these effects are attributed to dynamics, because small distortions can easily disrupt the exact cancellation of the individual dipoles (which are quite strong) associated with each end of the molecule. The molecule can exist in two forms, with both the bromines in an axial geometry or both in an equatorial position. Interconversion between these forms is observed, as in the parent cyclohexane. The single NMR line observed at low magnetic fields is due to fast exchange and requires that the two forms have roughly equal populations. Spectra obtained at low temperature confirm this, and variable-temperature studies allow measurement of the rates, leading to an enthalpy of activation of 62 kJ mol-1. More details of the interconversion are provided by some new calculation methods. Even for a relatively small molecule like this, calculation of a full potential energy surface is prohibitive. However, methods are now available to follow the molecule along the reaction coordinate in quite an efficient way. The results of these calculations lead to an extremely detailed picture of chair-chair interconversion in a di- and tetrasubstituted six-membered ring of the cyclohexane family. © 2011 American Chemical Society. Fil:Baron, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Kowalewski, V.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_10895639_v115_n33_p9207_Bain |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
Calculation methods Carbon atoms Centrosymmetric Crystalline solids Cyclohexane ring Different solvents Enthalpy of activation Equatorial positions Field intensity Flexible molecules Interconversions Low magnetic fields Low temperatures NMR spectrum Proton NMR Reaction coordinates Room temperature Six-membered rings Small molecules Structure and dynamics Vapor Phase Variable temperature X-ray diffraction studies Behavioral research Bromine Conformations Magnetic fields Molecules Nuclear magnetic resonance Nuclear magnetic resonance spectroscopy Protons Quantum chemistry X ray diffraction Cyclohexane |
| spellingShingle |
Calculation methods Carbon atoms Centrosymmetric Crystalline solids Cyclohexane ring Different solvents Enthalpy of activation Equatorial positions Field intensity Flexible molecules Interconversions Low magnetic fields Low temperatures NMR spectrum Proton NMR Reaction coordinates Room temperature Six-membered rings Small molecules Structure and dynamics Vapor Phase Variable temperature X-ray diffraction studies Behavioral research Bromine Conformations Magnetic fields Molecules Nuclear magnetic resonance Nuclear magnetic resonance spectroscopy Protons Quantum chemistry X ray diffraction Cyclohexane Bain, A.D. Baron, M. Burger, S.K. Kowalewski, V.J. Rodríguez, M.B. Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| topic_facet |
Calculation methods Carbon atoms Centrosymmetric Crystalline solids Cyclohexane ring Different solvents Enthalpy of activation Equatorial positions Field intensity Flexible molecules Interconversions Low magnetic fields Low temperatures NMR spectrum Proton NMR Reaction coordinates Room temperature Six-membered rings Small molecules Structure and dynamics Vapor Phase Variable temperature X-ray diffraction studies Behavioral research Bromine Conformations Magnetic fields Molecules Nuclear magnetic resonance Nuclear magnetic resonance spectroscopy Protons Quantum chemistry X ray diffraction Cyclohexane |
| description |
Cyclohexane is an extremely flexible molecule that oscillates, at room temperature, between two clearly distinct and extreme conformations that cannot be distinguished at room temperature; so much so that the NMR spectrum is a single line that includes all 12 protons be they axial or equatorial. This raises the interesting question as to what happens when there are equal substituents at the 1 and 4 carbon atoms of the ring. Therefore substitution in the 1,4-positions in the cyclohexane ring has been the subject of considerable interest because some form of interconversion between extreme conformations could lead to the existence of a rather unusual behavior. To study this problem, the interconversion in (di- or tetra-1,4)-substituted six-membered cyclohexane-type rings, trans-1,4-dibromo-1,4-dicyanocyclohexane, was found to be a particularly suitable candidate. Although X-ray diffraction studies on the crystalline solid found the molecule to be centrosymmetric, it still shows a significant dipole moment μ in solution, as determined with a procedure that leads to the vapor phase values of μ. Furthermore, the low magnetic field proton NMR spectrum at ambient temperature appears as a single line, a situation that changes with increasing field intensity and different solvents. Both these effects are attributed to dynamics, because small distortions can easily disrupt the exact cancellation of the individual dipoles (which are quite strong) associated with each end of the molecule. The molecule can exist in two forms, with both the bromines in an axial geometry or both in an equatorial position. Interconversion between these forms is observed, as in the parent cyclohexane. The single NMR line observed at low magnetic fields is due to fast exchange and requires that the two forms have roughly equal populations. Spectra obtained at low temperature confirm this, and variable-temperature studies allow measurement of the rates, leading to an enthalpy of activation of 62 kJ mol-1. More details of the interconversion are provided by some new calculation methods. Even for a relatively small molecule like this, calculation of a full potential energy surface is prohibitive. However, methods are now available to follow the molecule along the reaction coordinate in quite an efficient way. The results of these calculations lead to an extremely detailed picture of chair-chair interconversion in a di- and tetrasubstituted six-membered ring of the cyclohexane family. © 2011 American Chemical Society. |
| format |
JOUR |
| author |
Bain, A.D. Baron, M. Burger, S.K. Kowalewski, V.J. Rodríguez, M.B. |
| author_facet |
Bain, A.D. Baron, M. Burger, S.K. Kowalewski, V.J. Rodríguez, M.B. |
| author_sort |
Bain, A.D. |
| title |
Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| title_short |
Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| title_full |
Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| title_fullStr |
Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| title_full_unstemmed |
Interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| title_sort |
interconversion study in 1,4-substituted six-membered cyclohexane-type rings. structure and dynamics of trans -1,4-dibromo-1,4-dicyanocyclohexane |
| url |
http://hdl.handle.net/20.500.12110/paper_10895639_v115_n33_p9207_Bain |
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