Autocorrelated 13c‐13c double quantum coherence two‐dimensional nmr spectroscopy: Utilization of a modified version of the technique as an adjunct in the total assignment of the 1h‐ and 13c‐nmr spectra of the mutagen phenanthro[3,4‐b]thiophene

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Abstract
Development of successively higher field nmr spectrometers has facilitated the study of increasingly more complex molecules, although smaller molecules such as phenanthro[3,4‐b]thiophene still offer very substantial assignment problems because of the highly congested nature of their 1H‐ and 13C‐nmr spectra. Assignments of such spectra, if they are to be unequivocal, frequently require the utilization of two‐dimensional nmr spectroscopic techniques. Total assignments of the 1H‐ and 13C‐nmr spectra of phenanthro[3,4‐b]thiophene are reported. Assignments were based on a conventional high resolution 500 MHz 1H‐nmr spectrum, autocorrelated two‐dimensional 1H‐nmr spectra (COSY), two‐dimensional 1H‐13C chemical shift correlation spectra and a modified version of autocorrelated 13C‐13C double quantum coherence two‐dimensional nmr spectroscopy. From NOE measurements, a separation of 1.99 Å between H1 and H11 was computed, suggesting that phenanthro[3,4‐b]thiophene has a pronounced helical conformation in solution.