Conformational preferences of 3-(dimethylazinoyl)propanoic acid as a function of pH and solvent; intermolecular versus intramolecular hydrogen bonding.
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.
Nkansah
Richard A
RA
Crellin Laboratory of Chemistry, California Institute of Technology, Pasadena, California 91125, USA.
Liu
Yang
Y
Alley
Olivia J
OJ
Gerken
James B
JB
Drake
Michael D
MD
Roberts
John D
JD
D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008968:Molecular Conformation; D011422:Propionates / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry
D011422:Propionates; D012997:Solvents; C029658:propionic acid