Chiral Induction from Allenes into Twisted 1,1,4,4-Tetracyanobuta-1,3-dienes (TCBDs): Conformational Assignment by Circular Dichroism Spectroscopy

The mechanism of chiral induction in an optically pure 1,3-diethynylallene, from the central chiral allene moiety into directly adjacent TCBD chromophores, was confirmed and clarified. Only one low-energy conformer is found in calcns. of the potential energy surface, which closely resembles the X-ray crystal structure. Simulations of the CD spectrum by time-dependent DFT showed a total agreement, in terms of position and sign, for all Cotton effects when compared to the exptl. spectrum