Spectroscopic Analysis of Phenols

The ready reversibility of this reaction is essential to the role that quinones play in cellular respiration, the process by which an orgaitism uses molecular oxygen to convert its food to carbon dioxide, water, and energy. Electrons are not transferred directly from the substrate molecule to oxygen but instead are transferred by way of an electron transport chain involving a succession of oxidation-reduction reactions. A key component of this electron transport chain is the substance known as ubiquinone, or coenzyme Q  

The name ubiquinone is a shortened form of ubiquitous quinone, a term coined to describe the observation that this substance can be found in all cells. The length of its side chain varies among different organisms the most common form in vertebrates has n = 10, and ubiquinones in which n = 6 to 9 are found in yeasts and plants. 

Another physiologically important quinone is vitamin K. Here K stands for koagulation (Danish) because this substance was first identified as essential for the normal clotting of blood. 

Some vitamin K is provided in the normal diet, but a large proportion of that required by humans is produced by their intestinal flora. 

Intestinal flora is a general term for the bacteria, yeast, and fungi that live in the large intestine. 

NMR Compared with C—H, the carbon of C—O in a phenol is deshielded by about 25 ppm. In the case of m-cresol, for example, the C—O carbon gives the signal at lowest field. 

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Notice, too, that the most shielded carbons of the aromatic ring are the ones that are jhe cNMR spectrum of 

UV-VIS Just as with arylamines (Section 22.20), it is informative to look at the UV-VIS behavior of phenols in terms of how the OH group affects the benzene chromophore. 

An OH group affects the UV-VIS spectrum of benzene in a way similar to that of an NH2 group, but to a smaller extent. In basic solution, in which OH is converted to 0 , however, the shift to longer wavelengths exceeds that of an NH2 group. 

Mass Spectrometry A peak for the molecular ion is usually quite prominent in the mass spectra of phenols. It is, for example, the most intense peak in phenol. 

Phenol is both an important industrial chemical and the parent of a large class of compounds widely distributed as natural products. Although ben-zenol is the systematic name for CgHsOH, the lUPAC rules permit phenol to be used instead. Substituted derivatives are named on the basis of phenol as the parent compound. 

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Oxidation of Phenols Quinones 932 Spectroscopic Analysis of Phenols 933 Summary 935... 

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