The use of proton magnetic resonance spectroscopy in assigning the absolute configuration of coordination complexes containing optically active propylenediamine ligands

Steric prohibition of the inversion pathway. Test of the orbital symmetry prediction of the sense of rotation in thermal suprafacial 1,3-sigmatropic rearrangements

“…In reactions proceeding by this rotational mode, the increment of strain energy between the reactant and the transition state caused by methyl-ring repulsions would be larger for the case endo-methyl reactant (3) -* inside methyl transition state (5) than for the case exo-methyl (2) -*• outside methyl (4). Conversely, if the rotations were for some reason contra orbital symmetry (counterclockwise, CCW), the situation would be reversed, since such rotations would relieve methyl-ring repulsive strain in the e/iifo-methyl reactant and increase it in the exo.6…”

Hydroxy acid complexes. I. Complexes containing optically active lactic acid and pantoic acid

“…Nuclear Magnetic Resonance.-Proton magnetic resonance has been well established as a method of studying the conformations of chelate rings and assigning the absolute configurations of cobalt(III) complexes. [23][24][25][26][27][28][29] The nmr data for the reaction products and optically active forms of the complexes are given in Table II and it can be seen that the diastereomers prepared containing optically active lactic and pantoic acids show significant differences in the chemical shifts of the methyl and methine protons. A discussion of the chemical shifts involving the magnetic anisotropy of the C-N single bonds of the ethylenediamine rings would require the postulation of a variable anisotropy, and the differences are better explained in terms of van der Waals interaction29 or steric interactions between atoms.…”