The 353 nm nπ* transition of 4H-pyran-4-one and a deuterated derivative

Abstract

The 353 nm vapour absorption of 4H-pyran-4-one, and its 3,5-d2 derivative, has been measured and assigned to a forbidden, 1A2 (nπ*)–1A1 electronic transition, with electronic origin near 28 360 cm−1, made allowed by vibrations involving out-of-plane ring and C—H motions. Although the molecule remains planar upon excitation, other effects of conjugation on the nature of the excited state are less marked than in 2-cyclopenten-1-one.