Sordo, Jose AngelVarela-Alvarez, AdrianGiani, SamueleVogel, Pierre2010-11-302010-11-302010-11-30200810.1016/j.apcata.2007.07.048https://infoscience.epfl.ch/handle/20.500.14299/61516WOS:000254453100012Protonation of norbom-5-en-2-one gives 6-oxo-2-norbomyl cation (2) as most stable C7H9O+ cation. Quantum calculations at B3LYP/6-31G(d) level (gas phase, 1 atm, 25 degrees C) predict a C-s-structure for 2 that can be represented as an intramolecular pi-complex (Dewar pi-complex model) of an acetylium ion with an alkene (cyclopent-3-enyl moiety). Isomeric 5-oxo-2-norbornyl (1) cation is calculated to be 16.7 kcal/mol less stable than 2. Part of the relatively high stability of 2 arises from the electron-releasing carbonyl group through n(C=O) <-> sigma <-> 2p(C+) hyperconjugation. This effect is also present in more stable 6-oxo-3-oxa (14) and 6-oxo-3-aza-2-norbornyl cation (19) as these ions are calculated to be 7.4 and 3.3 kcal/ mol, respectively, more stable than their 5-oxo isomers. (c) 2007 Elsevier B.V. All rights reserved.carbocationsfrangomeric effecthyperconjugationWagner-Meerwein rearrangement norbornylcationpi-complexesClassical Norbornyl CationThrough-Bond InteractionsDerivatives Naked Sugars2-Norbornyl CationBeta-CarbonylAlpha-PineneNmr-SpectraGas-PhaseAb-InitioLone-Pairtext::journal::journal article::research article