Web Release Date: March 2,
Electronic and Molecular Structure of Aminimides
(1-Acyl-2,2,2-trimethyldiazan-2-ium-1-ide). 1. Formaminimide (HCON-N+Me3)
and
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and Physical Sciences Inc., Andover, Massachusetts 01810
Received: September 28, 2005
In Final Form: January 26, 2006
Abstract:
The electronic structure and geometries of (Z)- and (E)-H-CON-N+(CH3)3 have been examined at two levels
of theory: B3LYP (basis sets 6-311+G(d,p), 6-311++G(d,p), and 6-311G(3df,3pd)) and MP2(full)/6-311++G(d,p). The (Z) conformation about the C(O)-N- bond is thermodynamically preferred over the (E)
configuration. Natural bond orbital calculation locates one lone pair of the N- in the HOMO, which is the pz
natural hybrid orbital (perpendicular to the O=CN-N+ plane). The second lone pair (of lower energy) of N-
occupies the HOMO-3, which is the natural hybrid orbital sp1.12 (sp1.01 for the (E) conformation, sp1.74 in the
rotational transition state). The carbonyl 
bond is the HOMO-2. The charge-transfer ability of the negative
nitrogen in H-CON-N+(CH3)3 is more powerful than that of the neutral amidic nitrogen in dimethylformamide.
The following facts convincingly sustain this view: (1) the higher rotational barrier (stronger C-N- bond)
in the case of H-CON-N+(CH3)3, (2) natural resonance theory analysis predicts almost equal weights for
the (Z)-H-C(=O)N-N+(CH3)3 and the (Z)-H-C(O-)=NN+(CH3)3 canonical resonance structures whereas
the weight of the HCON(CH3)2 structure is almost twice as large as that of HC(O-)=N+(CH3)2, and (3) the
second-order perturbation stabilization, as a result of the donor (N-)/acceptor (carbonyl) interaction, is 101.3
kcal/mol for H-CON-N+(CH3)3 and only 64.4 kcal/mol for dimethylformamide.
Download the full text: PDF | HTML
