Photochromic Reactions, Substituent Effects and Fatigue Resistance of Phenyl Fulgides

Photochromic Reaction, Substituent Effects, and Fatigue Resistance of Phenyl Fulgides 

8a-DHNs undergo irreversible side reactions that include thermal disrotatory ring opening, a thermal 1,5-hydrogen shift to yield 1,2-dihydronaphtha-lene derivatives (1,2-DHNs), and in some cases, oxidation to the fully aromatic compound. 

The rate constants for the thermal disrotatory ring opening and 1,5-H shift reactions of some l,8a-DHNs (compounds 26 and 27) are listed in Tables 4.3 and 4.4, respectively. 

From the relationships between temperature and rate constants, the activation energy for the 1,5-H shift process in compound 27 has been calculated to be 33 kJ mol-1.21 

The side reactions of l,8a-DHNs were due to the 8a-hydrogen. Replacement of the 8a-hydrogen by a methyl group can eliminate the //-shift reactions and prevent the thermal disrotatory ring opening reaction. However, the photocyclization and photo-opening reaction are little affected, based on their conrotatory reaction 

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