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

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 1 H‐ and 13 C‐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 1 H‐ and 13 C‐nmr spectra of phenanthro[3,4‐ b ]thiophene are reported. Assignments were based on a conventional high resolution 500 MHz 1 H‐nmr spectrum, autocorrelated two‐dimensional 1 H‐nmr spectra (COSY), two‐dimensional 1 H‐ 13 C chemical shift correlation spectra and a modified version of autocorrelated 13 C‐ 13 C 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.