CCSD calculations structure

Quantum chemical calculations predict the primary ethylcation, C H/" to have /(-hydrido-bridgcd structure 5 which is 6-8 kcal/mol more stable than the Kekule line-bond structure for the primary cation 4. The ethylcation is not stable enough to be observable directly in superacid media. The NMR chemical shifts were calculated for both isomers 4 and 5 using the GIAO-MP2 method for CCSD optimized structures.23... 

Wiberg KB, Wang Y-G, de Oliveira AE, Perera SA, Vaccaro PH (2005) Comparison of CIS and EOM-CCSD-calculated adiabatic excited states structures. Change in charge density on going to adiabatic excited states. J Phys Chan 109 466-477... 

By assuming additivity in the style of the G2 procedure (Section 5.5), the CCSD(T)/ 6-31G(d,p) results may be combined with the changes due to basis set enlargement to 6-31 lG(2df,2pd) at the MP2 level and the zero-point energy corrections calculated at the MP2/6-31G(d,p) level. The results are shown in Table 11.31. From the observed accuracy of 2 kcal/mol for structures 2-8, the energetics of the species 9-11 may be assumed to be reliable to the same level of accuracy. 

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