Quinone methides characterization

Much attention has been devoted to the development of methods to generate quinone methides photochemically,1,19-20 since this provides temporal and spatial control over their formation (and subsequent reaction). In addition, the ability to photogenerate quinone methides enables their study using time-resolved absorption techniques (such as nanosecond laser flash photolysis (LFP)).21 This chapter covers the most important methods for the photogeneration of ortho-, meta-, and para-quinone methides. In addition, spectral and reactivity data are discussed for quinone methides that are characterized by LFP. 

Wan s group investigated a number of phenyl-substituted hydroxybiphenylbenzyl alcohols in the hope that the a-phenyl quinone methides photogenerated from them might show enhanced absorption and lifetimes, and thus be easier to characterize by LFP.37,38 They were successfully able to photogenerate and characterize quinone... 

Using the same reaction, Cole and Wan later photogenerated mcta-quinone methides 110-112 from the appropriate m-hydroxy-a-phenylstyrenes.78 The three were characterized by LFP, with 110 and 111 showing strong and sharp absorptions at 430 and 450 nm, respectively, similar to those observed for 104 and 105. The dimethoxy-susbstituted 112 showed a much broader absorption centered at 420 nm. Addition of the electron-donating methoxy groups stabilized the quinone methides the lifetimes of 110-112 in 1 1 aqueous acetonitrile were 5-200 times longer than that of 104. 

Quinone methide complexes were characterized by standard spectroscopic techniques. It is possible to elucidate the structural and electronic properties of the QM complexes and also to estimate the reactivity tendencies of the coordinated QM moiety based on IR, NMR, and X-ray diffraction spectroscopes. 

Dyall, L. K. Winstein, S. Nuclear magnetic resonance spectra and characterization of some quinone methides. J. Am. Chem. Soc. 1972, 94, 2196-2199. 

CHARACTERIZING QUINONE METHIDES BY SPECTRAL GLOBAL FITTING AND 13 C LABELING... 

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