“…C 7 H 9 + 6 . The bishomo square-pyramidal ion 6 was originally prepared by Masamune et al in superacid SbF 5 −SO 2 ClF solution at −110 ° C. The MP2/6-31G* optimized structure of 6 is given in Figure . We also searched for minimum-energy trishomocyclopropenium-type structure (Scheme ).…”
Section: Resultsmentioning
confidence: 99%
“…Although the parent cation (CH) 5 + has not yet been observed experimentally, a variety of similar structures − have been identified under stable ion conditions using 13 C and 1 H NMR spectroscopy. The pentagonal-pyramidal structure was observed for the (CCH 3 ) 6 2+ dication: …”
Section: Introductionmentioning
confidence: 99%
“…Although the parent cation (CH) 5 + has not yet been observed experimentally, a variety of similar structures [6][7][8][9][10] have been identified under stable ion conditions using 13 C and 1 H NMR spectroscopy. The pentagonal-pyramidal structure was observed for the (CCH 3 ) 6 2+ dication: 11 The (CH) 5 + cation has also been a subject of many theoretical studies first by semiempirical and later by ab initio methods.…”
The structures of hypercoordinate square-pyramidal carbocations were calculated at the correlated MP2/6-31G* level. The 13 C NMR chemical shifts of the cations were also calculated using IGLO and GIAO-MP2 methods. The IGLO calculated data show only a reasonable correlation with the experimental 13 C NMR chemical shifts. The correlated GIAO-MP2 calculated 13 C NMR shifts, however, showed significant improvements over the SCF IGLO calculated chemical shifts. It was also found that among the C 8 H 9 + isomers, the bishomo square-pyramidal cation 7 is only 0.2 kcal/mol more stable than the trishomocyclopropeniumtype ion 8 at the MP4(SDQ)/6-31G*//MP2/6-31G* + ZPE level. Almost a calculated 1:2 equilibrium mixture of ions 7 and 8 seems to best represent the experimental NMR spectrum of C 8 H 9 + at -80 °C. The structures and 13 C NMR chemical shifts for the elusive (CH) 5 + 1 and its monomethyl-substituted analogues 2 and 3 were also computed.
“…C 7 H 9 + 6 . The bishomo square-pyramidal ion 6 was originally prepared by Masamune et al in superacid SbF 5 −SO 2 ClF solution at −110 ° C. The MP2/6-31G* optimized structure of 6 is given in Figure . We also searched for minimum-energy trishomocyclopropenium-type structure (Scheme ).…”
Section: Resultsmentioning
confidence: 99%
“…Although the parent cation (CH) 5 + has not yet been observed experimentally, a variety of similar structures − have been identified under stable ion conditions using 13 C and 1 H NMR spectroscopy. The pentagonal-pyramidal structure was observed for the (CCH 3 ) 6 2+ dication: …”
Section: Introductionmentioning
confidence: 99%
“…Although the parent cation (CH) 5 + has not yet been observed experimentally, a variety of similar structures [6][7][8][9][10] have been identified under stable ion conditions using 13 C and 1 H NMR spectroscopy. The pentagonal-pyramidal structure was observed for the (CCH 3 ) 6 2+ dication: 11 The (CH) 5 + cation has also been a subject of many theoretical studies first by semiempirical and later by ab initio methods.…”
The structures of hypercoordinate square-pyramidal carbocations were calculated at the correlated MP2/6-31G* level. The 13 C NMR chemical shifts of the cations were also calculated using IGLO and GIAO-MP2 methods. The IGLO calculated data show only a reasonable correlation with the experimental 13 C NMR chemical shifts. The correlated GIAO-MP2 calculated 13 C NMR shifts, however, showed significant improvements over the SCF IGLO calculated chemical shifts. It was also found that among the C 8 H 9 + isomers, the bishomo square-pyramidal cation 7 is only 0.2 kcal/mol more stable than the trishomocyclopropeniumtype ion 8 at the MP4(SDQ)/6-31G*//MP2/6-31G* + ZPE level. Almost a calculated 1:2 equilibrium mixture of ions 7 and 8 seems to best represent the experimental NMR spectrum of C 8 H 9 + at -80 °C. The structures and 13 C NMR chemical shifts for the elusive (CH) 5 + 1 and its monomethyl-substituted analogues 2 and 3 were also computed.
“…In fact, ion 622 could be synthesized by reacting 620 with triflic acid. 1096 The obtained 1 H and 13 C NMR data could be explained with the intermediacy of the bishomo square pyramidal ion 631, although no conclusive distinction could be made between rapidly equilibrating systems of 630 and 631 structures. ð3:148Þ Although experimental work on the parent square pyramidal (CH) 5 þ ion has not been reported, a dimethyl-substituted derivative 623 of the pyramidal ion 615, however, has been prepared by Masamune et al 1095,1096 and studied by 1 H and 13 C NMR spectroscopy.…”
mentioning
confidence: 91%
“…The calculated bond distance for 621 is 1.36 Å and 1.351 Å (reported by Lambert et al 1089 and by M€ uller, 1091 respectively). ð3:148Þ Although experimental work on the parent square pyramidal (CH) 5 þ ion has not been reported, a dimethyl-substituted derivative 623 of the pyramidal ion 615, however, has been prepared by Masamune et al 1095,1096 and studied by 1 H and 13 C NMR spectroscopy. In the synthesis performed by Lambert, cation 622 was most probably formed by protonation of some acid impurity.…”
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