Molecular structure of tert-butylazide: A gas-phase electron diffraction and quantum chemical study

The molecular structure of tert-butylazide has been determined by gas-phase electron diffraction and quantum chemical calculations. The HF/6-31G* and B3LYP/6-31G** calculations yielded near C-5, symmetry for the tert-butyl gr oup, anti conformation of the (C)N-N bond with respect to one of the (N)C-C (H-3) bonds, and an essentially free rotation around the (C)N-N(Nr bond wit h a 0.34 kcal/mol energy difference between syn and anti conformations of t he CNNN moiety, the anti being the more stable form. The electron diffracti on analysis was carried out by modeling a mixture of conformational isomers , generated by rotating the terminal nitrogen of the azide group, using a c omputed rotational potential. The data are consistent with C, symmetry for the tert-butyl group. The (C)N-N bond, however, was found to be rotated out of the anti position, with respect to one of the (N)C-CH3 bonds, by 12.5(1 2)degrees. The electron diffraction analysis yielded the following bond len gths (r(g)), bond angles, and torsional angles: C-H 1.111(5) Angstrom, (N-N )(terminal) 1.143(4) Angstrom, (N-N)central 1.240(5) Angstrom, N-C 1.508(5) Angstrom, (C-C)mean 1.534(3) Angstrom, N-N-N 171.8(20)degrees N-N-C 118.6( 10)degrees N-C-C 102.5(6)degrees and 110.5(4)degrees, C-C-H 111.2(4)degrees , C-C-C 110.2(7)degrees and 112.6(7)degrees, N-N-C-C 167.5(12)degrees 50.1( 6)degrees, and -75.2(10)degrees.