Stable carbocations. 208. Carbon-13 nuclear magnetic resonance spectroscopic study of alkyl cations. The constancy of carbon-13 nuclear magnetic resonance methyl substituent effects and their application in the study of equilibrating carbocations and the mechanism of some rearrangements

Protonated tert-pentyl dication (C5H122+, isopentane dication)

“…The tert-pentyl cation can readily be obtained from the ionization of corresponding tert-pentyl halides in superacidic medium as reported by Olah and Donovan. 16 The structure of the cation in superacid solution was characterized by 1 H and 13 C NMR spectroscopy. 16 Two structures of the tert-pentyl cation, C-C hyperconjugatively stabilized 1 and C-H hyperconjugatively stabilized 2, were found to be minima at the ab initio MP2/6-31G* level as reported by Schleyer et al 17 At the MP4(SDTQ)/6-31G**//MP2/6-31G* + ZPE level the structure 1 was computed to be only 0.03 kcal mol −1 more stable than the structure 2.…”

Reactions in Zeolites

“…No peak in the area of 330 ppm was seen, thereby ruling out a carbenium ion resonating in the area reported by Olah. 6 Furthermore, no line shifts were evident with changes in temperature, thereby ruling out exchange. A small resonance at 123 ppm from carbon-carbon double bonds was observed.…”

Computational NMR of charged systems

“…The intriguing isopropyl cation, "a small persistent secondary carbocation generated in superacidic solution," was theoretically studied by Rasul et al [39] In the related experimental studies, the authors reported a doublet at 5.03 ppm and a septuplet at 13.5 ppm corresponding to the methyl and methine groups in the 1 H NMR spectrum [40] and resonances at 320.6 ppm for the carbocationic carbon and 51.5 ppm for the methyl groups in the corresponding 13 C NMR spectrum. [41] In the relevant calculations, [39] five stationary points 1a-1e were found for 1 that are shown in Figure 1 with the most stable conformation, 1c, having C 2 symmetry. All geometry optimizations were performed at the MP2/cc-pVTZ level while 1 H and 13 C NMR chemical shifts were calculated at the SCF, MP2, and CCSD(T) levels using TZP and TZ2P basis sets both for carbons and hydrogens.…”