Cyclopropyl Semidiones

Acidities and homolytic bond dissociation enthalpies of 4‐substituted‐2,6‐di‐tert‐butylphenols

“…(Examination of the ESR spectrum of hybrid radicals of this type has shown that the spin density of the odd electron resides principally on carbon. 14) The BDEs of the 0-H bonds in 4-methyl-2,6-ditert-butylphenol, 4-methoxy-2,6-di-tert-butylphenol and a-tocopherol of 80.1, 79.6 and 80.9 kcal, respectively (Table l), are in good agreement with the recently reported values of 80.7, 7 7 6 and 78.9 kcal, respectively, obtained by equilibrations with 2,4,6-tri-tertbutylphenol, BDE = 81.2 kcal, as a ~tandard. '~ Examination of Table 1 shows that a-tocopherol is less acidic than 4-methoxy-2,6-di-tert-butylphenol by 2 pK,, units, and is evidently less subject to steric inhibition of solvation.…”

Conformational studies of acyclic semidiones

“…However, the ketyl is unstable, and the signal disappears after thirty minutes, Dicyclopropyl ketyl (Figure 11c) gives the strongest signal of the series, a triplet of 5.5 gauss (46,55,57 This represents a a^/a^ equal to 6.2 and is consistent with a normal ratio of 6.5 (68).…”

“…The radical was generated in greater than 50^ yield from the acyloin as compared with a diphenylpicrylhydrazyl standard and was stable for days. This un usual stability may be connected with deloealized structures such as A and B in diagram 25 (46 …”

Semidiones in the bicyclo [3.1.0] hexane system

“…The most stable conformation of cyclopropyl semidiones (10) has been shown to have the a cyclopropyl hydrogen in the nodal plane of ,the semidione "IT system 5- The latter may result from 1,3 cr-Vf interaction 12.…”