Determination of the Rate Constant for H Atom Abstraction by Phenyl Radicals for THF and CH3CN
Abstract
Phenyl radicals are known to rapidly abstract hydrogens and add to double bonds and H-abstraction, particularly from the deoxyribose rings of DNA, is known to have biological significance. However, rate constants for H-abstraction (kH) by phenyl radicals from biomolecules are largely unknown. This research used p-fluorophenyl radicals generated by the photolysis of p-fluorophenylazoisobutyronitrile (FPAIN), to allow for product yields to be measured using F-19 NMR. Specifically, the rate constant for phenyl radical iodine abstraction from a 3-iodobenzotrifluoride (kI= 2.2 x 108 M-1 s-1) measured previously in our lab was used as a kinetic reference point for determining kH for hydrogen abstraction from tetrahydrofuran (THF) and acetonitrile (CH3CN). Thus, when FPAIN was photolyzed in the presence of THF or CH3CN and 3-iodobenzotrifluoride (ArI) at 23 °C the product yield ratio of p-hydro- to p-iodofluorobenzene ([FPhH]/[FPhI]) gave an excellent linear correlation (R2= 0.9985 and R2 = 0.9655) with the reactant concentration ratio ([THF]/[ArI]) and ([CH3CN]/[ArI]). The slope of the trendline (slope = 0.048 and slope = 0.0024) gives the relative rate constants kH/kI, which in conjunction with the previously determined kI = 2.2 x 108 M-1 s-1, gives kH. The THF result, kH = 1.1 x 107 M-1 s-1 at 23 °C compares favorably to the literature value kH = 4.8 x 106 M-1 s-1. The CH3CN preliminary results determined kH = 5.08 x 105 M-1s-1 which is compared to literature values reported by Galli (kH = 6.7 x 106 M-1 s-1) and Bridger and Scaiano (kH = 4.0 x 105 M-1 s-1).
College
College of Science & Engineering
Department
Chemistry
Campus
Winona
First Advisor/Mentor
Thomas Nalli
Start Date
4-19-2023 2:00 PM
End Date
4-19-2023 3:00 PM
Presentation Type
Poster Session
Format of Presentation or Performance
In-Person
Session
2b=2pm-3pm
Poster Number
36
Determination of the Rate Constant for H Atom Abstraction by Phenyl Radicals for THF and CH3CN
Phenyl radicals are known to rapidly abstract hydrogens and add to double bonds and H-abstraction, particularly from the deoxyribose rings of DNA, is known to have biological significance. However, rate constants for H-abstraction (kH) by phenyl radicals from biomolecules are largely unknown. This research used p-fluorophenyl radicals generated by the photolysis of p-fluorophenylazoisobutyronitrile (FPAIN), to allow for product yields to be measured using F-19 NMR. Specifically, the rate constant for phenyl radical iodine abstraction from a 3-iodobenzotrifluoride (kI= 2.2 x 108 M-1 s-1) measured previously in our lab was used as a kinetic reference point for determining kH for hydrogen abstraction from tetrahydrofuran (THF) and acetonitrile (CH3CN). Thus, when FPAIN was photolyzed in the presence of THF or CH3CN and 3-iodobenzotrifluoride (ArI) at 23 °C the product yield ratio of p-hydro- to p-iodofluorobenzene ([FPhH]/[FPhI]) gave an excellent linear correlation (R2= 0.9985 and R2 = 0.9655) with the reactant concentration ratio ([THF]/[ArI]) and ([CH3CN]/[ArI]). The slope of the trendline (slope = 0.048 and slope = 0.0024) gives the relative rate constants kH/kI, which in conjunction with the previously determined kI = 2.2 x 108 M-1 s-1, gives kH. The THF result, kH = 1.1 x 107 M-1 s-1 at 23 °C compares favorably to the literature value kH = 4.8 x 106 M-1 s-1. The CH3CN preliminary results determined kH = 5.08 x 105 M-1s-1 which is compared to literature values reported by Galli (kH = 6.7 x 106 M-1 s-1) and Bridger and Scaiano (kH = 4.0 x 105 M-1 s-1).
