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| Title: | Structural studies of nonclassical cyclobutylmethyl cations by the ab initio method |
| Author (s): | Reddy, Prakash Rasul, Golam Prakash, G.K. Surya Olah, George A. |
| Department/Lab Affiliations: | Center for Environmental Science and Technology (CEST) Chemistry |
| Keywords: | DFT calculations cyclobutylmethyl cation delocalized species |
| Issue Date: | 2007 |
| Publisher: | American Chemical Society ACS |
| Citation: | Reddy, V. Prakash, Golam Rasul, G.K. Surya Prakash, and George A. Olah. "Structural Studies of Nonclassical Cyclobutylmethyl Cations by the ab initio Method", J. Org. Chem. 2007, 72, 3076-3080. |
| Abstract: | Ab initio calculations at the MP2/cc-pVTZ level show that the cyclobutylmethyl cation is a nonclassical -delocalized species, which is distinct from the global minimum C2-symmetric cyclopentyl cation (Schleyer, P. v. R.; Carneiro, J. W. de M.; Koch, W.; Raghavachari, K. J. Am. Chem. Soc. 1989, 111, 5475). Relatively lower level DFT calculations, on the other hand, show that the primary cyclobutylmethyl cation spontaneously collapses into the cyclopentyl cation (Prakash, G. K. S.; Reddy, V. P.; Rasul, G.; Casanova, J.; Olah, G. A. J. Am. Chem. Soc. 1998, 120, 13362). The secondary 1-cyclobutylethyl cation is also a nonclassical carbocation, as shown by calculations at the MP2/cc-pVTZ level. Two structures having energy minima are identified for the latter cation on the potential energy surface. The conformer in which the methyl group is in the exo orientation is a global minimum and is favored over the corresponding endo conformer by 1.2 kcal/mol at the MP2/cc-pVTZ//MP2/cc-pVTZ +ZPE level of calculations. The tertiary 1-cyclobutyl-1-methylethyl cation, at this level of calculations, also involves substantial nonclassical -delocalization, showing that the nonclassical stabilization is more important for cyclobutylmethyl cations relative to the cyclopropylmethyl cations. The 13C NMR chemical shifts obtained from GIAO-CCSD(T)/tzp/dz calculations further substantiate the nonclassical structures for these carbocations. |
| Type: | Article - Journal text |
| In Title: | Journal of Inorganic Chemistry |
| Copyright Notice: | Pre-print: author cannot archive; Post-print: author cannot archive; This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. FULL COPYRIGHT INFORMATION: |
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| title | Structural studies of nonclassical cyclobutylmethyl cations by the ab initio method |
| contributor.author | Reddy, Prakash |
| contributor.author | Rasul, Golam |
| contributor.author | Prakash, G.K. Surya |
| contributor.author | Olah, George A. |
| contributor.deptlab | Center for Environmental Science and Technology (CEST) |
| contributor.deptlab | Chemistry |
| contributor.sponsor | American Chemical Society Petroleum Research Fund |
| contributor.sponsor | National Science Foundation |
| subject | DFT calculations |
| subject | cyclobutylmethyl cation |
| subject | delocalized species |
| date.issued | 2007 |
| publisher | American Chemical Society ACS |
| identifier.citation | Reddy, V. Prakash, Golam Rasul, G.K. Surya Prakash, and George A. Olah. "Structural Studies of Nonclassical Cyclobutylmethyl Cations by the ab initio Method", J. Org. Chem. 2007, 72, 3076-3080. |
| identifier.pub.URI | |
| description.abstract | Ab initio calculations at the MP2/cc-pVTZ level show that the cyclobutylmethyl cation is a nonclassical -delocalized species, which is distinct from the global minimum C2-symmetric cyclopentyl cation (Schleyer, P. v. R.; Carneiro, J. W. de M.; Koch, W.; Raghavachari, K. J. Am. Chem. Soc. 1989, 111, 5475). Relatively lower level DFT calculations, on the other hand, show that the primary cyclobutylmethyl cation spontaneously collapses into the cyclopentyl cation (Prakash, G. K. S.; Reddy, V. P.; Rasul, G.; Casanova, J.; Olah, G. A. J. Am. Chem. Soc. 1998, 120, 13362). The secondary 1-cyclobutylethyl cation is also a nonclassical carbocation, as shown by calculations at the MP2/cc-pVTZ level. Two structures having energy minima are identified for the latter cation on the potential energy surface. The conformer in which the methyl group is in the exo orientation is a global minimum and is favored over the corresponding endo conformer by 1.2 kcal/mol at the MP2/cc-pVTZ//MP2/cc-pVTZ +ZPE level of calculations. The tertiary 1-cyclobutyl-1-methylethyl cation, at this level of calculations, also involves substantial nonclassical -delocalization, showing that the nonclassical stabilization is more important for cyclobutylmethyl cations relative to the cyclopropylmethyl cations. The 13C NMR chemical shifts obtained from GIAO-CCSD(T)/tzp/dz calculations further substantiate the nonclassical structures for these carbocations. |
| type | Article - Journal |
| type.DCMIType | text |
| rights | Pre-print: author cannot archive; Post-print: author cannot archive; |
| rights | This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. |
| rights.URI | |
| rights.URI | |
| relation.isPartOf | Journal of Inorganic Chemistry |
| date.available | 2008-06-27T16:44:03Z |
| identifier.persist.URI |