Study of the conformational equilibria of some 2-(2?-hydroxyphenyl)-4-aryl-3H-1,5-benzodiazepines using1H,13C, and15N NMR spectroscopy
摘要:
Variable temperature H-1 NMR experiments of 2-(2'-hydroxyphenyl)-4-phenyl-3H-1,5-benzodiazepine (5a) and its derivatives 5d and 5e were carried out in order to investigate the conformational behaviour of these compounds. The Delta G* values for the ring inversion barriers of 5a and 5d are ca. 52 kJ/mol, i.e. they do not differ significantly as compared to analogous compounds without phenolic OH group(s). This indicates that the hydrogen bond has not to be opened during the inversion process. In 5e the barrier is about 2-3 kJ/mol higher which can be explained by steric interference between the additional methoxy group and the H-3 atoms during ring inversion. (NNMR)-N-15 data which can be discussed in terms of hydrogen bond strength support this interpretation.