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Conformational Equilibria of β-Alanine and Related Compounds as Studied by NMR Spectroscopy

Gregoire, Françoise and Wei, Sindy H. and Streed, Erik W. and Brameld, Kenneth A. and Fort, Diana and Hanely, Linda J. and Walls, Jamie D. and Goddard, William A. and Roberts, John D. (1998) Conformational Equilibria of β-Alanine and Related Compounds as Studied by NMR Spectroscopy. Journal of the American Chemical Society, 120 (30). pp. 7537-7543. ISSN 0002-7863. http://resolver.caltech.edu/CaltechAUTHORS:20151001-101405448

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Abstract

The vicinal proton−proton couplings of the dipolar form of β-alanine in water, alcohol−water, and dimethyl sulfoxide−water solutions indicate little conformational preference and are consistent with an essentially statistical equilibrium of the gauche or trans conformations. The position of the equilibrium is only slightly affected, over a temperature range of about 130°, by changes in dielectric constants ranging from 30 to 80 or by massive changes in ionic strength. Quantum-mechanical calculations at the HF/6-31G^(**) and LMP2/cc-pVTZ levels were found to give rather good parallels with experiment, although suggesting the gauche conformation to be 2−3 kcal/mol more stable in water or methanol than actually observed. A number of related compounds, such as N,N,N-trimethyl-β-alanine and N,N-diethyl-β-alanine, as well as the conjugate acid and conjugate base of β-alanine, also show no significant conformational preference in water solution. In conformity with these results, the zwitterionic form of piperidine-3-carboxylic acid (nipecotic acid) has about the same preference for equatorial carboxylate as cyclohexanecarboxylic acid itself. Taurine shows no significant conformational preference except in basic solution, where the couplings indicate about 53% of the gauche conformation. In contrast, N,N,N-trimethyltaurine is predominantly trans in acidic or neutral solution. The conformational equilibria of the N,N,N-trimethyltaurine species are most likely governed by steric hindrance, because there are rather large tetrahedral groups at each end of the ethano chains. Yet, even here the energy difference between gauche and trans is only about 1.2 kcal.


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http://dx.doi.org/10.1021/ja974311uDOIArticle
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Additional Information:© 1998 American Chemical Society. Received December 22, 1997. Revised Manuscript Received May 13, 1998. Publication Date (Web): July 16, 1998. is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for support of this research. We are also deeply indebted to the Summer Undergraduate Research Fellowship Program (SURF), the Beckman Institute of the California Institute of Technology, the E. I. Du Pont Company, and Dr. and Mrs. Chester M. McCloskey for their helpful financial assistance. Helpful suggestions were supplied by Professor J. D. Dunitz. The quantum chemistry calculations reported here were funded by DOE-BCTR (DE-FG36-93CH10581, David Boron). The facilities of the MSC are also supported by grants from NSF (CHE 95-22179 and ASC 92-100368), Chevron Petroleum Technology Co., Saudi Aramco, Asahi Chemical, Owens-Corning, Exxon, Chevron Chemical Co., Chevron Research and Technology Co., Avery-Dennison, Hercules, BP Chemical, and the Beckman Institute.
Funders:
Funding AgencyGrant Number
American Chemical Society Petroleum Research FundUNSPECIFIED
Caltech Summer Undergraduate Research Fellowship (SURF)UNSPECIFIED
E. I. Du Pont CompanyUNSPECIFIED
Dr. and Mrs. Chester M. McCloskeyUNSPECIFIED
Department of Energy (DOE)DE-FG36-93CH10581
NSFCHE 95-22179
NSFASC 92-100368
Chevron Petroleum Technology Co.UNSPECIFIED
Saudi AramcoUNSPECIFIED
Asahi ChemicalUNSPECIFIED
Owens-CorningUNSPECIFIED
ExxonUNSPECIFIED
Chevron Chemical CoUNSPECIFIED
Chevron Research and Technology Co.UNSPECIFIED
Avery-DennisonUNSPECIFIED
HerculesUNSPECIFIED
BP ChemicalUNSPECIFIED
Caltech Beckman InstituteUNSPECIFIED
Record Number:CaltechAUTHORS:20151001-101405448
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20151001-101405448
Official Citation:Conformational Equilibria of β-Alanine and Related Compounds as Studied by NMR Spectroscopy Françoise Gregoire, Sindy H. Wei, Erik W. Streed, Kenneth A. Brameld, Diana Fort, Linda J. Hanely, Jamie D. Walls, William A. Goddard, and John D. Roberts Journal of the American Chemical Society 1998 120 (30), 7537-7543 DOI: 10.1021/ja974311u
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:60662
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:02 Oct 2015 16:12
Last Modified:02 Oct 2015 16:12

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