Photochemistry of the vitamin D series. I. Kinetics and quantum yields in ergosterin irradiation by lambda = 253,7 nm

Irradiation of Δ^5,7-9α, 10β-steroids in solution with λ = 253,7 nm yielded no Δ^5,7-9β, 10α-steroids and vice versa. No back reaction from precalciferol₂ to ergosterol could be detected by kinetic measurements. This leads to the conclusion that with the mercury resonance line only ring opening and 6,7-cis/trans isomerization but no ring closure occurs.