QUANTITATIVE FIELD DESORPTION MASS-SPECTROMETRY .18. POLAR [4+2]-PHOTOCYCLOADDITIONS AND [4+4]-PHOTOCYCLOADDITIONS - EFFECTS OF HYBRIDIZATION IN DIRADICALS

The control of photochemical reactions by polar substituents is of value for preparative applications. For example, anthracene 1a reacts with butadiene to give the [4+2]‐ 2a and the [4+4] adduct 3a in the ratio of 20:1. The carbonitrile 1b, on the other hand, leads to (2b), (3b), and 4 (secondary product of a 3b‐isomer) in the ratio of 1:3.2:13.3. The polar substituent thus suppresses the [4 + 2] reaction (a: X  H; b: X  CN). (Figure Presented.) Copyright © 1979 by Verlag Chemie, GmbH, Germany