Conformational preferences of 3-(dimethylazinoyl)propanoic acid as a function of pH and solvent; intermolecular versus intramolecular hydrogen bonding.
J Org Chem
; 74(6): 2344-9, 2009 Mar 20.
Article
em En
| MEDLINE
| ID: mdl-19245202
ABSTRACT
The conformational equilibrium of 3-(dimethylazinoyl)propanoic acid (DMAPA, azinoyl = N(+)(O(-)) has a weak pH-dependence in D(2)O, with a slight preference for trans in alkaline solutions. The acid ionization constants of the protonated amine oxide and carboxylic functional groups as determined by NMR spectroscopy were 7.9 x 10(-4) and 6.3 x 10(-6), respectively. The corresponding value of K(1)/K(2) of 1.3 x 10(2) is not deemed large enough to provide experimental NMR evidence for a significant degree of intramolecular hydrogen bonding in D(2)O. Conformational preferences of DMAPA are mostly close to statistical (gauche/trans = 2/1) in other protic solvents, e.g., alcohols. However, the un-ionized form of DMAPA appears to be strongly intramolecularly hydrogen-bonded and gauche in aprotic solvents.
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Base de dados:
MEDLINE
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Propionatos
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Ligação de Hidrogênio
Idioma:
En
Revista:
J Org Chem
Ano de publicação:
2009
Tipo de documento:
Article
País de afiliação:
Estados Unidos