Knowledge Bank

The microwave spectrum of seven isotopes of cis-hex-3-ene-1,5-diyne has been observed using a pulsed-nozzle Fourier transform spectrometer. The inertial defect of $0.43(amu-\backslash AA2)$ indicates planarity, as expected for this $\pi$-conjugated system. The $ro$ and $rs$ structures will be discussed and compared to results from ab initio calculations. The evidence for non-linearity in the alkyne arms (CCCH) will be discussed, given that this highly unsaturated molecule is the prototype hydrocarbon which undergoes the Bergman cyclization to benzenoid diradicals.