Stereodynamics of Diethylmethylamine and Triethylamine

Article abstract of DOI:10.1021/ja00387a012

Diethylamine is the simplest acyclic trialkylamine that possesses the requisite symmetry that allows, in principle, the direct observation of both nitrogen inversion and isolated nitrogen-carbon bond rotation using 1H dynamic nuclear magnetic resonance (DNMR) spectroscopy.DNMR studies of diethylmethylamine and two deuterated derivatives complemented by empirical force-field calculations reveal a comprehensive picture of the stereodynamics of this representative acyclic trialkylamine.The DNMR studies show clear evidence for pyramidal inversion at nitrogen.In addition to nitrogen inversion, the results also speak for several "families" of rotamers for diethylmethylamine that undergo very rapid, DNMR-invisible intrafamily conformational exchange via isolated N-CH2 rotation while also undergoing higher barrier DNMR-visible interfamily exchange also via isolated N-CH2 rotation.The DNMR-visible N-CH2 rotation processes involve CCH3/N-alkyl eclipsing in the transition state while the DNMR-invisible processes involve CCH3/lone pair eclipsing.Although the symmetry of triethylamine precludes the DNMR-observation of nitrogen inversion, (1)H DNMR evidence for restricted N-CH2 rotation and empirical force-field calculations reveal stereodynamics for triethylamine that are highly analogous to diethylmethylamine.