Elsevier

Tetrahedron

Volume 24, Issue 3, 1968, Pages 1407-1414
Tetrahedron

Solvent effects in NMR Spectroscopy : Solvent shifts of methoxyl resonances in flavones induced by benzene; an aid to structure elucidation

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Abstract

The position and relative orientation of OMe groups in methoxyflavones can be inferred from benzene-induced solvent shifts of the OMe resonances. OMe groups at C-5, C-7, C-10 and C-12 exhibit large positive Δ values (Δ = δCDC13 - δC6H6 ⋍ 0·5 to 0·8 ppm) in the absence of substituents ortho to these groups. In contrast, OMe groups at C-3, or those flanked by two ortho-OMe functions (or one ortho-OH and one orthoOMe function) show small positive or negative Δ values. An OMe at C-5 suffers a drastic algebraic decrease in solvent shift upon the introduction of an OMe group at C-6. Electronic and conformational factors which may account for these differences are considered.

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Present address: Department of Organic Chemistry, Adelaide, South Australia.

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