ChemInform Abstract: The Molecular Structure of Di-t-butylamine, NH(C(CH3)3)2, as Determined by Gas-Phase Electron Diffraction: an Exceptionally Sterically Hindered Amine.

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Abstract Gaseous di-t-butylamine, NHBut2, has been studied by electron diffraction at a nozzle temperature of ca. 293 K. The diffraction data reveal that this amine is exceedingly hindered. Repulsive steric interactions between the But groups are mainly relieved by an opening of the CNC valence angle to 135(3)°. Evidence of steric strain may also be found in the non-zero tilts (2–3°) of the But groups, defining the angle of rotation of these groups about axes through the N-bonded carbon atoms orthogonal to the NC2 plane. The NC and CC bonds, 1.467(13) and 1.561(6) A, respectively, are on the other hand relatively unstrained. Other principal geometrical parameters are unexceptional: CH = 1.103(10) A, ∠NCC = 111.3(1.5)° (mean value) and ∠CCH = 106(2)°. The position of the N-bonded hydrogen atom relative to the NC2 plane could not be determined. The torsional positions of the But groups, with respect to the NC bonds, could not be derived from least-squares refinements. A large number of models with But groups in various fixed positions were considered; the best fit between the observed and theoretical intensity data was obtained with one But group being twisted 19° away from the position typified by one CC bond of this group being anti to the remote NC bond, and the other But group similarly twisted by 30°. When viewed along the NC bonds, the But groups are twisted in the same direction. Viewed along the C(N)C axis, these groups come close to being staggered with respect to each other. The values of the above bond distances are those of ra parameters. Parenthesized values denote error limits, being least-squares standard deviations multiplied by a factor of three.