Ring inversion process for a series of 3,5-dialkyl-1-oxa-3,5- diazacyclohexanes: ~1H DNMR study and semiempirical calculations

摘要

The ring inversion process for a series of 3,5-dialkyl-1-oxa-3,5- diazacyclohexanes was studied using proton dynamic nuclear magnetic resonance (~1H DNMR) spectroscopy in conjunction with semiempirical calculations. At low temperature, the ring methylene protons decoalesced into two AB spin systems in a 2:1 ratio. Lineshape simulations of the DNMR spectra provided first-order rate constants for magnetic exchange. The energy barrier for each inversion reaction was calculated from the respective rate constants. In general, as the size of the N-alkyl group increased, the barrier to ring inversion decreased. A similar trend was seen in semiempirical calculations that modeled the ring inversion process.