Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes
The form of molecular vibrations, and changes in these, give valuable insights into geometric and electronic structure upon electronic excitation or ionization, and within families of molecules. Here, we give a description of the phenyl-ring-localized vibrational modes of the ground (S₀) electronic...
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Elsevier
2017
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| Online Access: | https://eprints.nottingham.ac.uk/47620/ |
| _version_ | 1848797590554935296 |
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| author | Tuttle, William D. Gardner, Adrian M. Andrejeva, Anna Kemp, David Wakefield, Jonathan C.A. Wright, Timothy G. |
| author_facet | Tuttle, William D. Gardner, Adrian M. Andrejeva, Anna Kemp, David Wakefield, Jonathan C.A. Wright, Timothy G. |
| author_sort | Tuttle, William D. |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | The form of molecular vibrations, and changes in these, give valuable insights into geometric and electronic structure upon electronic excitation or ionization, and within families of molecules. Here, we give a description of the phenyl-ring-localized vibrational modes of the ground (S₀) electronic states of a wide range of ortho-disubstituted benzene molecules including both symmetrically- and asymmetrically-substituted cases. We conclude that the use of the commonly-used Wilson or Varsányi mode labels, which are based on the vibrational motions of benzene itself, is misleading and ambiguous. In addition, we also find the use of the Mi labels for monosubstituted benzenes [A. M. Gardner and T. G. Wright. J. Chem. Phys. 135 (2011) 114305], or the recently-suggested labels for para-disubstituted benzenes [A. Andrejeva, A. M. Gardner, W. D. Tuttle, and T. G. Wright, J. Molec. Spectrosc. 321, 28 (2016)] are not appropriate. Instead, we label the modes consistently based upon the Mulliken (Herzberg) method for the modes of ortho-difluorobenzene (pDFB) under Cs symmetry, since we wish the labelling scheme to cover both symmetrically- and asymmetrically-substituted molecules. By studying the vibrational wavenumbers from the same force field while varying the mass of the substituent, we are able to identify the corresponding modes across a wide range of molecules and hence provide consistent assignments. We assign the vibrations of the following sets of molecules: the symmetric o-dihalobenzenes, o-xylene and catechol (o-dihydroxybenzene); and the asymmetric o-dihalobenzenes, o-halotoluenes, o-halophenols and o-cresol. In the symmetrically-substituted species, we find a pair of in-phase and out-of-phase carbon-substituent stretches, and this motion persists in asymmetrically-substituted molecules for heavier substituents. When at least one of the substituents is light, then we find that these evolve into localized carbon-substituent stretches. |
| first_indexed | 2025-11-14T20:06:18Z |
| format | Article |
| id | nottingham-47620 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| last_indexed | 2025-11-14T20:06:18Z |
| publishDate | 2017 |
| publisher | Elsevier |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-476202020-05-04T19:13:14Z https://eprints.nottingham.ac.uk/47620/ Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes Tuttle, William D. Gardner, Adrian M. Andrejeva, Anna Kemp, David Wakefield, Jonathan C.A. Wright, Timothy G. The form of molecular vibrations, and changes in these, give valuable insights into geometric and electronic structure upon electronic excitation or ionization, and within families of molecules. Here, we give a description of the phenyl-ring-localized vibrational modes of the ground (S₀) electronic states of a wide range of ortho-disubstituted benzene molecules including both symmetrically- and asymmetrically-substituted cases. We conclude that the use of the commonly-used Wilson or Varsányi mode labels, which are based on the vibrational motions of benzene itself, is misleading and ambiguous. In addition, we also find the use of the Mi labels for monosubstituted benzenes [A. M. Gardner and T. G. Wright. J. Chem. Phys. 135 (2011) 114305], or the recently-suggested labels for para-disubstituted benzenes [A. Andrejeva, A. M. Gardner, W. D. Tuttle, and T. G. Wright, J. Molec. Spectrosc. 321, 28 (2016)] are not appropriate. Instead, we label the modes consistently based upon the Mulliken (Herzberg) method for the modes of ortho-difluorobenzene (pDFB) under Cs symmetry, since we wish the labelling scheme to cover both symmetrically- and asymmetrically-substituted molecules. By studying the vibrational wavenumbers from the same force field while varying the mass of the substituent, we are able to identify the corresponding modes across a wide range of molecules and hence provide consistent assignments. We assign the vibrations of the following sets of molecules: the symmetric o-dihalobenzenes, o-xylene and catechol (o-dihydroxybenzene); and the asymmetric o-dihalobenzenes, o-halotoluenes, o-halophenols and o-cresol. In the symmetrically-substituted species, we find a pair of in-phase and out-of-phase carbon-substituent stretches, and this motion persists in asymmetrically-substituted molecules for heavier substituents. When at least one of the substituents is light, then we find that these evolve into localized carbon-substituent stretches. Elsevier 2017-10-21 Article PeerReviewed Tuttle, William D., Gardner, Adrian M., Andrejeva, Anna, Kemp, David, Wakefield, Jonathan C.A. and Wright, Timothy G. (2017) Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes. Journal of Molecular Spectroscopy, 344 . pp. 46-60. ISSN 0022-2852 Vibrations Frequencies Ground electronic state ortho-Disubstituted Benzenes http://www.sciencedirect.com/science/article/pii/S0022285217304034?via%3Dihub doi:10.1016/j.jms.2017.10.011 doi:10.1016/j.jms.2017.10.011 |
| spellingShingle | Vibrations Frequencies Ground electronic state ortho-Disubstituted Benzenes Tuttle, William D. Gardner, Adrian M. Andrejeva, Anna Kemp, David Wakefield, Jonathan C.A. Wright, Timothy G. Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title | Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title_full | Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title_fullStr | Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title_full_unstemmed | Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title_short | Consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| title_sort | consistent assignment of the vibrations of symmetric and asymmetric ortho-disubstituted benzenes |
| topic | Vibrations Frequencies Ground electronic state ortho-Disubstituted Benzenes |
| url | https://eprints.nottingham.ac.uk/47620/ https://eprints.nottingham.ac.uk/47620/ https://eprints.nottingham.ac.uk/47620/ |