Polar vs. bde effects on aldehydic hydrogen atom transfer reactions of benzaldehydes by t-butoxy radicals.

Chemistry of Acyl Radicals

“…The Arrhenius expression for the hydrogen abstraction from PhCHO by tert -butoxyl radicals was found to be log( k /M -1 s -1 ) = 8.8 − 1.3/θ, where θ = 2.3 RT kcal mol -1 . Relative rate constants for H-atom abstraction from substituted benzaldehydes ( p -Me, m -Me, p -Cl, m -Cl, p -Br, m -F, m -CF 3 , and m -CN) have also been reported, and a ρ + value of −0.32 was rationalized in terms of a polar contribution to the transition state. , …”

“…46 Relative rate constants for H-atom abstraction from substituted benzaldehydes (p-Me, m-Me, p-Cl, m-Cl, p-Br, m-F, m-CF 3 , and m-CN) have also been reported, and a F + value of -0.32 was rationalized in terms of a polar contribution to the transition state. 101,102 Some rate constants for the reaction of HOO • , RC(O)OO • , and ROO • radicals with a variety of aldehydes have been obtained from studies on the oxidation of aldehydes. [103][104][105] The reactivities of the aldehydes toward a HOO • radical decrease by 1 order of magnitude along the series t-BuCHO > c-C 6 H 11 -CHO > n-C 6 H 13 CHO > C 6 H 5 CHO, and this trend has been attributed to the inductive effect of the R group attached to the CHO moiety.…”

“…Early work on the cyclization of 6-heptenoyl radicals was conducted by Cekovic who studied the reaction of citronelloyl chloride (99) with tributyltin hydride (Scheme 106) and obtained a 43% yield of an unspecified mixture of menthone and isomenthone (101). 238 Bachi and Denenmark studied the identical reaction several years later and obtained an 85% yield of cyclized products with a 60/40 menthone/ isomenthone ratio.…”

Photoinduced Generation of Acyl Radicals from Simple Aldehydes, Access to 3-Acyl-4-arylcoumarin Derivatives, and Evaluation of Their Antiandrogenic Activities

“…Competing experiments with p -anisaldehyde 2c and 4-fluorobenzaldehyde 2e were performed to reveal the electronic effect of the aldehyde. As a result, coumarin 3ac , which was generated by reaction with 2c , was observed as a major product, and the electron-rich aldehyde was superior to the electron-poor aldehyde, as reported previously . To evaluate the role of BPO, the reaction was performed without catalyst (eq 5).…”