AA BB spin system

The preference for conformer 5e has also been established for 3-alkyl-3-aryl thietane oxides194, based mainly on the analysis of the AA BB spin system of the ring hydrogens in the NMR spectrum. 

The 1H NMR spectrum of the four central protons of 48h was analyzed as an AA BB spin system. The coupling constants between II7/II7 and the deuterium nuclei on C6/C6 (ca 2 Hz) were taken into account as first-order perturbations. In all cases coupling constants over four (—0.58 to —0.87 Hz) and five (+0.32 to +0.69 Hz) bonds were also considered in performing the spectral analysis. Chemical shifts and vicinal coupling constants for 48a-f are reported in Table 14. 

P and 13C NMR data are more informative. Thus the 31P ttj NMR spectrum of the complex is a sharp singlet at 50°C, which converts into a pattern of lines characteristic of an AA BB spin system upon cooling at -40°C. On the other hand the P NMR of a sample of the complex, approximately 50% enriched in C02, clearly shows the three central lines of the 1 4 6 4 1 quintet expected for an isotopic mixture of the three possible isotopomers, while the C spectrum of this enriched sample displays a quintet at S 206 ppm (2Jcp=18Hz) due to the C02 ligands. A full description of these NMR properties can be found elsewhere (Alvarez et al, 1986). From these data, structure A can be proposed for this... 

Figure 23. (A) Aromatic region of the convolution difference H-NMR spectrum at 360 MHz of a BPTl solution in HjO, pD = 7.8 = 26°. (B) Double-resonance irradiation at 7.07 ppm causes the collapse of a doublet at 7.33 ppm. (C) Irradiation at 7.33 ppm causes the collapse of a doublet at 7.07 ppm. The assignment of this AA BB spin system to residue 10 is from Reference 67. From [68].

Tribenzocyclyne is a bright yellow solid which decomposes at 215-220°C. The NMR spectrum (CDCI3) exhibits multiplets centered at 7.32 (6H) and 7.17 S (6H) typical of an AA BB spin system. The NMR spectrum (CDCI3) exhibits peaks at 132.0, 128.6, 126.7, and 92.9 5. A very weak C=C stretch is observed at 2217cm in the IR spectrum. Mass spectroscopic evidence indicates a parent ion at mje = 300. 

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