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Stereodynamics of N-tert-Butyl-NJV-dialkylamines. Experimental and Theoretical Evidence for a Common Potential Surface for tert-Butyl Rotation and Nitrogen Inversion C. Hackett Bushweller,* Warren G . Anderson, Philip E. Stevenson, David L. Burkey, and James W. O’Neil Contribution from the Department of Chemistry, Worcester Polytechnic Institute, Worcester, Massachusetts 01609. Received December 26, 1973
Abstract: Examination of the ’H dnmr spectra of a series of N-tert-butyl-N,N-dialkylamines revealed spectral changes consistent with slowing tert-butyl rotation and in appropriate compounds changes corresponding to slowing the nitrogen inversion-rotation process. In each compound where rerr-butyl rotation and nitrogen inversion could be observed simultaneously, the activation parameters for the two processes are identical within experimental error. The experimental results are rationalized on the basis of a common potential surface for tert-butyl rotation and nitrogen inversion and are consistent with intermediate neglect of differential overlap (INDO) calculations.
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ne of the important aspects of conformational analysis is an assessment of the rates of various types of stereomutation (e.g., bond rotation, pyramidal inversion, ring reversal) possible in a molecular system. Particularly in the case of simple systems, microwave,2 infrared, and Raman3 spectroscopy as well as thermodynamic measurements4 have been useful in determining barriers to simple intramolecular rate processes. Recently, dynamic nuclear magnetic resonance (dnmr)h spectroscopy has been applied very successfully to the study of rotation about carbon-carbon single bonds,6 carbon-nitrogen single bonds,7 carbon-phosphorus single bonds,8 and inversion about n i t r ~ g e n . ~ Although extensive experimental and theoretical studies indicate a substantial barrier (-30 kcal/mol) to pyramidal inversion about phosphorus in acyclic trialkylpho~phines,~~ nitrogen inversion in acyclic trialkylamines is a much more facile process (AH* < 9 (1) Alfred P.Sloan Research Fellow, 1971-1974; Camille and Henry Dreyfus Teacher-Scholar, 1972-present. (2) C. C. Lin and J. D. Swalen, Rec. Mod. Phys., 31,841 (1959). (3) J. R.Durig, S. M. Craven, C. W. Hawley, and J. Bragin, J . Chem. Phys., 57,131 (1972),and references therein. (4) I
