Molecular structure and dynamics, gas phase nuclear magnetic resonance spectroscopy, microwave spectroscopy, inter- and intramolecular energy transfer. Our research efforts are aimed at elucidating and understanding the structures, potential functions and dynamics of molecules which execute large amplitude motions such as internal rotations, ring inversions and pseudorotation. Toward this end we have developed powerful gas phase nuclear magnetic resonance and low resolution microwave spectroscopic techniques to address specific problems in these areas.
At UC Davis we have developed the use of pressure dependent gas phase NMR spectroscopy as a probe of conformational dynamics in the gas phase. Our present capabilities allow spectral acquisition at sample pressures as low as 0.1 torr. With these capabilities we are able to pursue studies which address both the accumulation and disposal of intramolecular and intermolecular vibrational energy in simple molecules undergoing structural exchange. Currently, gas phase NMR studies have been initiated on several other systems such as PF5, ethers and alkyl nitrites, and cyclic amines. Since, for many of these systems, it is possible to obtain rate data in the bimolecular kinetic region, we can probe intermolecular energy transfer efficiencies accompanying these processes. We also plan NMR studies of molecules in molecular beams.
Our current microwave studies are aimed at characterizing intramolecular vibrational redistribution in moderately sized molecules at low internal energies. We are also interested in obtaining potential functions for large amplitude vibrations such as internal rotation of large molecules. Recently, we determined the internal rotation potential function for benzyl fluoride by obtaining and analyzing the very high resolution microwave spectrum of this molecule.
Education, Awards and Professional Highlights
- Sloan Fellow (1986-1988)
- Presidential Young Investigator (1984-1989)
- Appointed to UC Davis faculty (1980)
- Postdoctoral Associate, Cornell University (1979-1980)
- Postdoctoral Associate, University of London (1978-1979)
- B.S.; Ph.D. University of Connecticut (1973; 1977)
- Taha, A.N., S.M. Neugebauer-Crawford, and N.S. True. 1998. Gas-phase 1H NMR studies of internal rotation activation energies and conformer stabilities of asymmetric N,N-disubstituted formanides and trifluoroacetamides. J. Phys. Chem. A, 102, 1425-1430.
- Taha, A.N., S.M. Neugebauer-Crawford, and N.S. True. 1998. Determination of the internal rotation barrier of 15N formamide from gas-phase NMR spectra. J. Amer. Chem. Soc., 120, 1934-1935.
- Neugebauer-Crawford, S.M., A.N. Taha, N.S. True, and C.B. LeMaster. 1997. Gas-Phase NMR studies of N, N-dimethylthioamides. Influence of the thiocarbonyl substituent on the internal rotation activation energies. J. Phys. Chem. A, 101, 4699-4706.
- Bohn, R.K., S.A. Sorenson, N.S. True, T. Brupbacher, M.C.L. Gerry, and W. Jager. 1997. The conformation and internal rotation barrier in benzyl fluoride from its microwave spectrum. J. Mol. Spectrosc., 184, 167-171.
- True, N.S. 1996. "Gas phase NMR studies of chemical exchange processes." In Encyclopedia of NMR. D.M. Grant and R.K. Harris, eds., John Wiley and Sons, 2173-2178.
- Suarez, C., M. Tafazzoli, N.S. True, S. Gerrard, C.B. LeMaster, and C.L. LeMaster. 1995. Gas phase 1H NMR study of N-ethyl methyl amides: Torsional barrier and conformer equilibria around the peptide bond. J. Phys. Chem., 99, 8170-8176.
- True, N.S. and C. Suarez. 1995. "Gas phase NMR studies of conformational processes." In Advances in Molecular Structure Research, Vol. 1. JAI Press, Inc., 115-155.
- Tafazzoli, M., C. Suarez, N.S. True, C.B. LeMaster, and C.L. LeMaster. 1994. The ring inversion of gaseous N-methylpiperazine. Pressure and temperature dependent 1H NMR Studies. J. Mol. Struct., 317, 137-145.
- Bohn, R.K., S.A. Sorenson and N.S. True. 1992. Rotational spectra of p-isopropyl-benzaldehyde. Assignment of two conformers and observation of torsionally excited states. J. Mol. Struct., 268, 97-106.
- Bohn, R.K., M.S. Farag, C.M. Ott, J. Radhakrishnan, S.A. Sorenson, and N.S. True. 1992. Rotational spectra of p-ansialdehyde. Assignment of the planar conformers and observation of torsionally excited states. J. Mol. Struct., 268, 107-121.
- Tafazzoli, M., S. Gerrard, N.S. True, and C.B. LeMaster. 1994. Gas and solution phase NMR studies of N-ethylmorpholine: Intra- and intermolecular effects on ring inversion rate constants. J. Mol. Struct., 317, 131-136.
- Sorenson, S.A., N.S. True, C.M. Ott, R.K. Bohn, and M.S. Farag. 1992. Temperature-dependent low-resolution microwave studies of m-iodoanisole, m-bromoanisole, m-nitroanisole and m-anisaldehyde. J. Mol. Struct., 268, 123-133.
- Tafazzoli, M., C. Suarez, N.S. True, C.B. LeMaster, and C.L. LeMaster, 1992. Pressure- and temperature-dependent 1H NMR studies of N-methylipiperidine ring inversion in the gas phase. J. Phys. Chem., 96, 10201-10205.
- Moreno, P.O., C. Suarez, M. Tafazzoli, N.S. True, and C.B. LeMaster. 1992. Gas-phase NMR study of the degenerate cope rearrangement of Bullvalene. J. Phys. Chem., 96, 10206-10212.
- Suarez, C., M. Tafazzoli and N.S. True. 1992. Gas-phase NMR spectra of cyclohexene are consistent with a barrier to ring inversion of less than 30 kj mol-1. J. Mol. Struct., 271, 89-94.