Molecular structure and photochemical reactivity. Part 7.—Vapor-phase photochemistry of cyclopropane carboxaldehyde

Abstract

Irradiation of cyclopropane carboxaldehyde in the vapour phase at 3130 Å and 120°C gives crotonaldehyde (Φ= 0.35), propylene (Φ= 0.25), and carbon monoxide (Φ= 0.30) as major products, with a variety of hydrocarbons in minor amounts. Experimental conditions were : temperature 100–200°C, light intensity 0.6 × 10¹⁴ to 1.1 × 10¹⁶ quanta absorbed cm^–3 sec^–1 and total pressure 17–154 mm. Cyclopropane is a major product at high temperatures (Φ= 0.76 at 200°C) or low light intensities (Φ= 0.23 at 120°C and 0.6 × 10¹⁴ quanta absorbed cm^–3 sec^–1). A mechanism is proposed involving reactions from two excited states. It is suggested that cyclopropane is formed in a free radical chain originating from one excited state and propylene is produced in a primary process from the other; crotonaldehyde is formed from both excited states. The ratio of radical to non-radical products is 1/3.