Knowledge Bank

Heptafulvene $(C8H8)$ is a nonalternant aromatic hydrocarbon with a seven-membered ring and an exocyclic double bond. Its microwave spectrum has been investigated in the frequency range from 26 to 40 GHz. A computer controlled microwave spectrometer was used to enhance the sensitivity for measuring a weak spectrum of an unstable compound. The rotational constants and electric dipole moment have been determined. The molecule was found to the planar. A series of excited states of a low frequency out-of-plane vibrational mode has also been observed.