Stereochemical effects on H-1 chemical shifts in 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) and related molecules

摘要

H-1-NMR spectra of DBH (1), DBO (2) and of the synthetic precursor to 1, 1,4-phenyl-2,4,6-triazatricyclo[5.2.1.0(2,6)]heptane-3,5-dione (5), were recorded in acetone-d(6) and C6D6 at 500 MHz. Assignment was aided by complete resolution of signals of 1 and 2 in C6D6 by aromatic solvent-induced shifts (ASIS). The effect of the change fi om phenyltriazolinedione to a diazene functional group on the chemical shifts of the exo,endo and syn,anti protons was investigated. The chemical shifts of the exo,endo protons of 1 are exceptionally sensitive to the functional group at the heterosubstituted bridge in the DBH skeleton. However, the relative chemical shift of the syn,anti proton pair is independent of the nature of the functional group. The role of stereochemical effects on these chemical shifts is discussed. [References: 21]