An-Najah Staff

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 t1leir 'H- and "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 'H- and "C-nmr spectra of phenanthro[3,4-b]thio­phene are reported. Assignments were based on a conventional high resolution 500 MHz 'H-nmr spectrum, autocorrelated two-dimensional 'H-nmr spectra (COSY), two-dimensional 'H-"C chemical shift correlation spectra and a modified version of autocorrelated "C-"C double quantum coherence two-dimensional nmr spectroscopy. From NOE measurements, a separation of 1.99 A between H1 and HII was computed, sugges­ting that phenanthro[3,4-b]thiophene has a pronounced helical conformation in solution.