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[摘要]：Uncatalyzed thermal decomposition (TD) and charge-transfer-induced decomposition (CTID) of dioxetanes were investigated to determine their thermodynamic characteristics. The dioxetanes examined were a series of 1-[4-(benzothiazol-2-yl)-3-hydroxyphenyl]-4,4-dimethyl-2,6,7-trioxabicy clo-[3.2.0]heptanes, 1a-d, bearing an alkyl substituent R, methyl, ethyl, isopropyl, or tert-butyl, at the 5-position and a parent dioxetane 1e with R = H. X-ray single crystallographic analysis was achieved for 1a-d. Both free energies of activation. Delta G double dagger(TD) and Delta G double dagger(CTID), increased in the order 1a <= 1b < 1c < 1d. The free energy difference Delta Delta G double dagger = Delta G double dagger(TD) - Delta G double dagger(CTID) was ca. 27 kJ mol(-1) regardless of the substituent R. However, the use of Taft's dual-substituent parameter suggested that CTID was more sensitive to the polarity of the substituent R than TD. The entropy term for CTID, Delta S double dagger(CTID), decreased from zero to a large negative value in the order of /err-butyl, isopropyl, ethyl, and methyl, whereas Delta S double dagger(TD) did not show a similar tendency. |
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