The anomeric effect in 1,3-benzodioxole: additional evidence from the rotational, vibration–rotation and rovibronic spectra

Abstract

The millimetre wave pure rotation and vibration–rotation spectrum of 1,3-benzodioxole has been studied and the vibrational spacing between the two lowest vibrational states in the five membered ring puckering potential has been determined with considerable accuracy, at ΔE₀₁ = 259 726.035(10) MHz or 8.663 5280(4) cm⁻¹. In addition, rotationally resolved analysis of two hot bands near the reported origin band in the laser-induced fluorescence spectrum has been carried out and was found to rule out the current literature assignment of this spectrum. The new information has been used to reassign the lowest vibrational transitions in the far-infrared and the Raman spectrum of 1,3-benzodioxole in terms of a one dimensional potential with a central barrier of 108 cm⁻¹, which successfully accounts for all states up to υ = 5, and for the observed variation in rotational constants. Considerable reassignment of the published spectra, as well as new experimental work is still necessary for a confident determination of the low-energy region of the molecular potential of 1,3-benzodioxole.