Getting a Grip on Nitrogen

Abstract

Chemistry Chirality is associated more with carbon than with nitrogen centers, as the latter atoms tend to invert their configurations fairly rapidly on account of their unbonded electron pair. Recently, relatively slow nitrogen inversion was observed in cyclic oligomers of four or six aza-β3–amino acids (β–amino acids in which nitrogen replaces the traditional carbon at the β position) on account of hydrogen bonding among the substituents. Mocquet et al. now show that swapping in a single analogous residue that is chiral at carbon disrupts the collective inversion mechanism and thereby dramatically stabilizes the chiral nitrogen conformations throughout the ring. A variety of nuclear magnetic resonance and x-ray diffraction studies revealed a stable syndiotactic arrangement of asymmetric nitrogen centers up to temperatures of 413 K. J. Am. Chem. Soc. 131 , 10.1021/ja9058074 (2009).