Nuclear Resonance in the Solid Methylamines. I

Abstract

Proton NMR lines have been studied in solid NH2CH3, NH(CH3)2, and N(CH3)3 from 4.2°K to the respective melting points. All the lines show a line-narrowing transition beginning, on warming, at about 40°, 65°, and 105°K, respectively. Second moments as well as peak-to-peak linewidths and line shapes have been measured in an attempt to determine the physical situation responsible for these transitions. Pure quadrupole resonances of 14N have also been observed in these compounds from 4.2°K to their melting points and the coupling constants and asymmetry parameters determined. A first-order phase change was detected in monomethylamine. This transition occurs at 55° ± 2°K on cooling and at 105° ± 2°K on warming. Two pairs of lines were seen in dimethylamine indicating two chemically inequivalent sites. Coupling constants (and asymmetry parameters) at 4.2°K are: monomethylamine 4.0180 MHz (0.3697), dimethylamine 4.6810 MHz (0.3339) and 4.6452 MHz (0.3228), and trimethylamine 5.2377 MHz (0).