Structure, vibrational absorption and circular dichroism spectra, and absolute configuration of Troger's Base

The structure of Troger's Base, 1, a heterocyclic amine containing two ster eogenic N atoms, is predicted from ab initio Density Functional Theory (DFT ), using the B3PW91 and B3LYP functionals and the 6-31G* basis set. Vibrati onal unpolarized absorption and vibrational circular dichroism (VCD) spectr a are predicted thence. in the case of VCD, Atomic Axial Tensors (AATs) are calculated using Gauge-invariant Atomic Orbitals (GIAOs). The predicted st ructure is in excellent agreement with the X-ray structure of 1. The predic ted vibrational spectra are in excellent agreement with experimental spectr a of CCl4 and CS2 solutions of 1, supporting the identicalness of the cryst alline and solution conformations of 1. No evidence of additional conformat ions of 1 in solution is found. The VCD spectra require the assignment of t he (R,R)/(S,S) absolute configuration to (-)/(+)-1, opposite to that obtain ed from the electronic circular dichroism spectrum by Mason et al. and in a ccord with that obtained from X-ray crystallography of a salt of 1 containi ng monoprotonated 1, 2, and a chiral anion by Wilen et al. The structure of 2 predicted by DFT is also in excellent agreement with the X-ray structure .