The computed value of 39.4 ± 3 kcal/mol18 for the activation energy of formation of 2 from 1 coupled with an A factor esti-mated18 at 1011•5 =*= °•6 gives k= 10-7 sec-1 for the slower diradical mechanism.(18) These parameters were estimated by group additivity methods described by (a) S.
Seven 2′‐hydroxychalcone derivatives with a methyl group on the 5′‐position were synthesized. Infrared absorption spectra of these new compounds are discussed.
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