How do ring currents affect (1)h NMR chemical shifts?
Conventional explanations of proton NMR chemical shifts need fundamental revisions. Ab initio (IGLO) analyses reveal that the downfield delta (1)H of benzene is not due to deshielding ring current effects; the shielding is less than the pi contribution to vinyl delta (1)Hs. Enhanced deshielding sigma CC influences are responsible for the more downfield delta (1)Hs of the inner protons of naphthalene and anthracene. Double pi effects shield ethynyl Hs; there is no evidence for a special "ring current influence."
Wannere
Chaitanya S
CS
Department of Chemistry, Computational Chemistry Annex, University of Georgia, Athens, Georgia 30602, USA.
Schleyer
Paul Von Ragué
PV