IGAIM method, chemical shift

The H and chemical shifts of some unsaturated species, their carbanions and the corresponding lithium complexes were calculated by the IGAIM method and compared with experimental values in THF solution. Examples are the lithium salt of the allyl carbanion (102), the dimeric form of the latter (103) and the lithium salt of the bicyclo[3.2.1]octa-3,6-dienyl carbanion (104) . 

Calculations using GIAO and IGAIM methods have enabled the chemical shifts of methyl cation and anion to be determined by gauging the shielding of the nucleus by neighbouring electrons the experimental data for cyclopentadienide ion, benzene, tropylium ion, and cyclooctatetraene dianion have also been reproduced and the data have been correlated by a simple model that also accounts for the large downfield shifts found for carbenes.14... 

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