Stereodinamics of N-Ethyl-N-methyl-2-aminobutane

Article abstract of DOI:10.1021/ja00230a001

N-Ethyl-N-methyl-2-aminobutane (EMAB) is the simplest acyclic trialkylamine which possesses a chiral carbon bonded to a chiral nitrogen.The chiral carbon is configurationally stable, while the chiral nitrogen is configurationally labile via nitrogen inversion.The 1H dynamic NMR (DNMR) spectra of three selectively deuteriated derivatives of EMAB show a decoalescence into four subspectra with relative populations of 49percent, 22percent, 17percent, and 12percent at 104 K.The DNMR behavior can be simulated in terms of a model which involves a relatively high barrier for interconversion between diastereomers via nitrogen inversion (ΔG<*>=7.3 kcal/mol) and lower barriers for conformational interconversion via isolated rotation (ΔG<*>=6.4 and 5.6 kcal/mol).By using the NMR data and complementary molecular mechanics calculations, the 49percent and 12percent subspectra are assigned to conformations of the R_CR_N and S_CS_N stereoisomers, while the 22percent and 17percent subspectra are assigned to the R_CS_N and S_CR_N stereoisomers.Preferred conformations have the N-ethyl methyl group in one of the two positions gauche to the nitrogen lone pair, the Cl methyl of the 2-butyl group anti to the lone pair, and the C4 methyl of the 2-butyl group syn periplanar to the lone pair.There is no experimental evidence for conformations which have the methine proton or the N-ethyl methyl group anti to the lone pair.