Radical Identification

As a second example of the use of radical identification in determining electrode reaction mechanisms, we consider the oxidation of triphenylacetic acid in acetonitrile. This was first studied by Kondrikov et who 

Different observations were made by Goodwin and coworkers, using the in situ cell of Bard and Goldberg described in Section 1. Their work was 

The case history of triphenylacetic acid provides a good example of the mechanistic detail that can be obtained from coupling electrochemistry with ESR. At the same time, note should be taken of the possible pitfalls both in cell design and in the interpretation of spectra. 

---

Force-field methods, calculation of molecular structure and energy by, 13,1 Free radical chain processes in aliphatic systems involving an electron-transfer reaction, 23, 271 Free radicals, and their reactions at low temperature using a rotating cryostat, study of, 8. I Free radicals, identification by electron spin resonance, 1, 284... 

Free radicals, identification by electron spin resonance, 1, 284 Gas-phase heterolysis, 3, 91... 

Reactive free radicals also react with the nitrogen of nitroso groups, forming a nitroxide one atom closer to the trapped radical than is the case with nitrone spin traps. This results in ESR spectra containing more chemical structural information. While nitroso spin traps provide radical identification, the resultant adducts are often less stable than those derived from nitrone traps. In particular, nitroso traps are unreliable for oxygen-centered radicals even in vitro. 

ESR is a sensitive tool for detecting free radicals. In addition, ESR represents further improvement over indirect methods normally employed in lignin investigations of free radicals by providing the possibility of specific free radical identification and characterization through spectroscopic detail. The characteristics of an ESR spectrum useful for deductions about physical interactions can be conveniently grouped into the following four parameters (1) g-value, (2) intensity, (3) line shape, and (4) hyperfine structure. 

The g-values of most organic free radicals are within 2% of the free electron value and thus do not provide a potentially powerful criterion for radical identification. However, Norman and Pritchett (115) have noted that substitution of hydroxy or alkoxy groups on the a-carbon in simple hydrocarbon radicals increases the g-value by about 0.001, while a-aldehydic or ketonic groups increase the value still higher, about 0.002. It has already been mentioned in Section II.B.2 that because of large spin-orbit coupling, most radicals with spin localized or heteroatoms, such as oxygen and sulfur, have g-values appreciably different from that of a free electron. These... 

---