Electronic spectra of the CH3CNCXY(X, Y=H, Cl) nitrile ylides: an ab initio multiconfigurational second-order quasidegenerate perturbation theory study

Multireference and multistate perturbation theory at second order (MC-QDPT2) based on a CASSCF wavefunction was used to study the electronic spectra of three nitrile ylides: CH3CNCH2, CH3CNCHCl and CH3CNCCl2. These ylides, which have an allene-like structure, present two characteristic transitions of n→π∗ type with λmax>200 nm. The longer-wavelength absorption has low intensity, while the shorter-wavelength absorption has a relatively strong intensity. These absorptions are predicted to occur at 312 and 272 nm (CH3CNCH2), 356 and 283 nm (CH3CNCHCl), and 377 and 305 nm (CH3CNCCl2).