Iso-chemical shielding surfaces

Kleinpeter and Koch have recently introduced spatial magnetic properties as a measure of homoaromaticity. These are calculated as through-space NMR shieldings (TSNMRS) and visualized as iso-chemical shielding surfaces (ICSF). The structures, the intramolecular flexibility, and the and C NMR chemical shifts are calculated on the MP2/6-311 + G level of theory. TSNMRS of benzene and the cyclopropenylium cation as prototype aromatic molecules published earlier are used as references for homoaromaticity in a number of homoaromatic carbocations. The existence and the degree of homoaromaticity are deduced from the TSNMRSs by comparing the experimental and computed H and NMR NMR chemical shifts. 

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