Orbital phase control of conformations of alkyne derivatives

Stable conformers of the alkynes bis-substituted by donor (NH2) and/or acceptor (CHO) groups were predicted by the orbital phase theory and confirmed by the ab initio and density functional calculations. The most stable conformers are planar in the mono-, di-, and triacetylenes substituted by a donor on terminal carbon atom and an acceptor on the other one. The stable conformers of those with donors or acceptors on both terminal carbon atoms are orthogonal. In the most stable conformers of the equatorial isomers of the hypervalent derivatives (RCCSiF4−: RNH2; CHO), the donor (nN) orbital and σSiFeq∗ with same πCC bond orbitals, or the acceptor (πCO∗) orbital and σSiFeq∗ interact with different πCC bond orbitals.