Rotations- und Inversionsprozesse in organischen Molekulen geben sich durch die Temperaturabhangigkeit der NMR-Spektren zu erkennen. Das Studium der Substituenteneffekte auf die Aktivierungsbarrieren solcher Prozesse gestattet die Aufklarung von Reaktionsmechanismen, ferner lassen sich die Stabilitatsgrenzen von Isomeren ermitteln. Die Kenntnis der Stabilitatsgrenzen ist notwendig, um gezielt stabile Rotamere und Invertomere synthetisieren zu konnen.

Nachweis gehinderter Rotationen und Inversionen durch NMR‐Spektroskopie

1H-Nmr was used to measure the rate of cis–trans interconversion of X-Pro bonds in linear and cyclic oligopeptides. k(cis → trans) = 2.5 × 10−3 s−1 at 25°C was found for the zwitterionic form of H-Ala-Pro-OH, in good agreement with earlier measurements. Replacement of Ala by Phe, Tyr, or Trp resulted in a 10-fold slower interconversion rate, whereas after substitution of Ala by His or Glu, the rate decreased only slightly. Independent of the residues X, the interconversion rate was increased by a factor of ca. 20 when the peptide chain was elongated by addition of Ala to the C-terminal Pro. An additional increase by a factor of 6 was observed when going from the protected linear peptide CF3CO-Gly-Gly-Pro-Ala-OCH3 to the closely related cyclic compound c[-Gly-Gly-Pro-Gly-Ala-]. These data are evaluated with regard to their possible use in future studies on the role of X-Pro cis–trans isomerization in the kinetics of protein folding.

Nmr studies of the rates of proline cis–trans isomerization in oligopeptides

Recent Advances in Atropisomerism

The Study of Intramolecular Rate Processes by Dynamic Nuclear Magnetic Resonance

Recent advances in atropisomerism

Studies of chemical exchange by nuclear magnetic resonance. III. Internal rotation in N,N-dimethylacetamide-d2 and a structure-reactivity correlation for the rotation reaction of amides

Effect of hydrogen bonding on the barrier to rotation about amide bonds

Chemical exchange by nuclear magnetic resonance. IV. Concentration dependence of the nuclear magnetic resonance spectral properties of some N,N-dimethylamides and -thioamides

Studies of chemical exchange by nuclear magnetic resonance. IX. Rotation about the amide bond in N,N-dimethylformamide

Studies of chemical exchange by nuclear magnetic resonance. X. Inherent carbon-nitrogen rotational barriers in amides, thioamides, and amidinium ions

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