H-1-NMR AND C-13-NMR STUDY OF NAPHTHO[2,1-B]THIOPHENE AND NAPHTHO[2,1-B]FURAN DERIVATIVES

A series of four substituted naphtho[2,1-b]thiophenes 1-4 and a series of five substituted naphtho[2,1-b] furans 5-9 have been studied using one-and two-dimensional H-1- and C-13-NMR methods. Chemical shifts of protons could not be assigned on the basis of the homonuclear correlation (COSY) spectra only, but two-dimensional nuclear Overhauser (NOESY) spectroscopy had to be used. The cross-peak between H1 and H9 enabled unequivocal assignation of the H6-H9 four proton spin system. On the bases of NOE measurements of the naphtho[2,1-b]thiophene 3, it was possible to estimate the interatom distances between H1 and H9 protons of 209 pm, and between H1 and H2 of 244 pm, respectively. Chemical shifts of substituted carbons were assigned using two-dimensional H-1/C-13 heteronuclear correlation (HETCOR) spectra. The substitution effect and the effect of solvent on the chemical shifts of the furan and thiophene analogues are reported, and the coupling constants (n)J(H,H) were determined.