Conformational Dynamics of Triple Rotors:  Tris(dimethylamino)methane, Triisopropylamine, and Related Molecules¹

Abstract

NMR spectra and their temperature-dependence are reported for tris(dimethylamino)methane (1), for tris(diethylamino)methane (2), for triisopropylamine (3), and for N,N-diisopropyl-3-pentylamine (4) and are discussed in terms of the conformations adopted and interconversion of these conformations, as indicated by molecular mechanics calculations. Solid state NMR spectra, obtained by freezing the neat liquids at low temperatures, were also used to support the conclusions of the conformational analysis. Proton NMR spectra of protonated forms of 3 and 4 were similarly analyzed. Less crowded triple rotors prefer a gauche, gauche, gauche conformation while more crowded ones adopt an anti, gauche, gauche arrangement.

Non-planar structures of Et3N and Pri3N: a contradiction between the X-ray, and NMR and electron diffraction data for Pri3N

“…These additional data therefore give a definite proof of the pyramidal structure of Pr i 3 N in the crystal and the static nature of the disordering. Our X-ray data for Pr i 3 N to a certain extent contradict earlier GED and NMR measurements 2,7,16 but they agree well with AM1, PM3 and ab initio calculations 9 giving a nonplanar structure for this molecule. However, we cannot totally exclude the possibility that the nonplanar structure of 3 may be enhanced by the crystal field effect.…”

“…This is a GED study of Pr i 3 N by Bock et al 16 [C-N-C = 119.2(3)°, C-N = 1.460(5) Å, C 3 symmetry with C-N-CA-HA = 5.0(18)°.] Although these data are mostly in line with NMR studies of this compound in solution and in the solid state, 2,7 there are some contradictions with the results of quantum chemical calculations of its molecular structure. 9 Thus, AM1 and PM3 methods predict a nonplanar structure (C-N-C = ca.…”

“…The stereodynamics of simple tertiary amines has been the subject of a few reviews 1 and original publications. [2][3][4][5][6][7][8][9] Most of these studies dealt with investigations into the dynamics of the inversion-rotation processes in amines and/or energetic molecular mechanics and quantum calculations. 9b The molecular structures of MeNH 2 , Me 2 NH, Me 3 N and Me 2 EtN were studied by the gas electron diffraction (GED) and microwave techniques, 10 Me 3 N was also studied in the solid state.…”

Conformational Studies by Dynamic NMR. 64.1Stereomutations of Atropisomers and of Conformational Enantiomers in Ethers of Hindered Naphthylcarbinols

“…When the enantiomerization equilibrium brings this tert -butyl back into its previous (hindered) position, the three methyl groups have exchanged their sites by making use of the rate constants k 1 and k 2 . A similar situation, related to the motions of a different molecule, has been recently described …”

Steric Hindrance Underestimated: It is a Long, Long Way to Tri-tert-alkylamines

“…Consequently, studies of the molecular structure were focused on 16 , which should be very nearly planar about nitrogen based on the results of electron diffraction studies . This outcome was claimed to be confirmed by NMR investigations, whereas low-temperature single-crystal X-ray diffraction of 16 led to a height of the NC 3 pyramid (nitrogen at the top) of 0.27–0.29 Å . This value is more than a half of the corresponding height in triethylamine (0.467 Å) .…”