Typical Proton Coupling Constants

Typical one-bond phosphorus-proton coupling constants... 

Although single bond carbon-13 proton coupling constants (Vch) show a dependency on the geometry of the ring, a value of 200 Hz is considered typical for a carbon attached to oxygen in a heteroaromatic system (B-72MI22203). Values for 2- and 4-pyranone and furan are presented in Table 11. 

In the C NMR spectrum two signals with unusually small shift values [(07/2)2 5c = 7.7 CH 5c = 10.6] and remarkably large CH coupling constants Jch= 161.9 and 160.1 Hz) indicate a mono-substituted cyclopropane ring A. The protons which belong to this structural unit at = 0.41 (AA ), 0.82 BB ) and 1.60 (M) with typical values for cis couplings 8.1 Hz) and trans couplings 4.9 Hz) of the cyclopropane protons can be identified from the CH COSY plot. 

The keto-carbonyl C signal at 5c = 200.9 would only fit the aflatoxins B, and M,. In the C NMR spectrum an enol ether-C// fragment can also be recognised from the chemical shift value of 5c = 145.8 and the typical one-bond coupling constant Jch = 196 Hz the proton involved appears at Sh = 72, as the CH COSY plot shows. The H triplet which belongs to it overlaps with a sing-... 

The multiplets and coupling constants of the axial) protons at = 3.15, 3.50 and 4.08 moreover confirm the equatorial positions of all three OH groups, as can be seen in formula B. Here the couplings from 10.0 to 11.5 Hz, respectively, identify vicinal protons in diaxial configurations, whilst values of 4.5 and 5.0 Hz, respectively, are typical for axial-equatorial relationships. As the multiplets show, the protons at 5 = 3.50 and 4.08 couple with two axial and one equatorial proton (triplet of doublets) respectively, whereas the proton at = 3.15 couples with one axial and one equatorial proton (doublet of doublets). 

First the five protons (integral) of the //NMR spectrum (Sfj = 7.50 - 7.94) in the chemical shift range appropriate for aromatics indicate a monosubstituted benzene ring with typical coupling constants 8.0 Hz for ortho protons, 1.5 Hz for meta protons.). The chemical shift values especially for the protons which are positioned ortho to the substituent Sn = 7.94) reflect a -M effect. Using the CH COLOC plot it can be established from the correlation signal hclS = 66.AI7.94 that it is a benzoyl group A. 

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