A. Haaland, H. Thomassen, Yngve Stenstr∅m
Dec 2, 1991
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Influential Citations
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Journal
Journal of Molecular Structure
Abstract
Abstract The molecular structure of trimethylamine N -oxide has been determined by gas electron diffraction with a nozzle temperature of 150° C and the structure and bonding investigated by HF MO calculations at the 6–31 G*level. Structure parameters from experiment ( r a ,∠ α ) and calculations ( r e ,∠ e ) are: NO, r a =137.9(3), r e =137.0 pm; CN, r a =149.6(2), r e =147.3 pm; ∠ α CNO=108.9 (2) °; ∠ e =108.7°. The uncertainties are estimated 2σ values. A scaled quantum mechanical force field has been derived. The calculated energy of the reaction Me 3 NO+pyr→Me 3 N+pyr·O; Δ U ° 298 =−7.1 kJ mol −1 , combined with the experimental NO bond dissociation enthalpy of pyridine N-oxide yields a NO dissociation enthalpy of Δ H ° 298 =295±6 kJ mol −1 in Me 3 NO. Comparison with the NO bond distances and bond energy terms in H 2N OH and XNO, X = H, Cl or F, shows that the NO bond strength in Me 3 NO is intermediate between normal single and double NO bonds. Population analysis indicates that if the O atom in the valence state (1s) 2 (2s) 2 (2p x ) 2 (2p y ) 2 is taken as the point of departure, NO bond formation is accompanied by donation of 0.84 electrons into the vacant pσ (2p z ) orbital and back donation of 0.08 electrons from each of the two pπ (2p x , 2p y ) orbitals.