Resonance methoxyphenol

In an attempt to delineate the degree of preservation of lignin in pre-Tertiary coal, we examined numerous coalified wood samples ranging in age from Carboniferous to Cretaceous. The samples were initially screened by solid-state l C nuclear magnetic resonance to detect the possible presence of methoxyl carbon. Once such carbons were detected, the samples were subjected to analytical pyrolysis to determine the relative yields of methoxyphenols which would provide an indication of the state of preservation of the lignin-derived structu units. We report here on the identification of lignin-derived methoxyphenols in the coalified wood samples selected for analytical pyrolysis. 

Hammett s equation was also established for substituted phenols from the elementary hydroxyl radical rate constants. The Hammett resonance constant was used to derive a QSAR model for substituted phenols. The simple Hammett equation has been shown to fail in the presence of electron-withdrawing or electron-donating substituents, such as an -OH group (Hansch and Leo, 1995). For this reason, the derived resonance constants such as o°, cr, and o+ were tested in different cases. In the case of multiple substituents, the resonance constants were summed. Figure 5.24 demonstrates a Hammett correlation for substituted phenols. The least-substituted compound, phenol, was used as a reference compound. Figure 5.24 shows the effects of different substituents on the degradation rates of phenols. Nitrophenol reacted the fastest, while methoxyphenol and hydroxyphenol reacted at a slower rate. This Hammett correlation can be used to predict degradation rate constants for compounds similar in structure. 

Antioxidants, such as 2,6-di-te/ /-butyl-4-mcthylphenol (also known as butylated hydroxytoluene or BHT) and 2-/ert-butyl-4-methoxyphenol (also known as butylated hydroxyanisole or BHA), are added to many organic materials to prevent autoxidation. They function by interfering with the autoxidation chain reaction. When a radical encounters an antioxidant molecule, such as BHA, it abstracts a hydrogen to produce a resonance-stabilized radical ... 

A tunable pulsed laser Raman spectrometer for time resolved Raman studies of radiation-chemical processes is described. This apparatus utilizes the state of art optical multichannel detection and a-nalysis techniques for data acquisition and electron pulse radiolysis for initiating the reactions. By using this technique the resonance Raman spectra of intermediates with absorption spectra in the 248-900 nm region, and mean lifetimes > 30 ns can be examined. This apparatus can be used to time resolve the vibrational spectral o-verlap between transients absorbing in the same region, and to follow their decay kinetics by monitoring the well resolved Raman peaks. For kinetic measurements at millisecond time scale, the Raman technique is preferable over optical absorption method where low frequency noise is quite bothersome. A time resolved Raman study of the pulse radiolytic oxidation of aqueous tetrafluoro-hydroquinone and p-methoxyphenol is briefly discussed. 

Figure 5. Resonance Raman spectra (1400-1700 cm ) of transient intermediates produced in the pulse radiolysis of a 2 mM aqueous solution of p-methoxyphenol (N20 saturated pH 11). Key a-d, the spectra obtained at different times (At) after the electron pulse d, the spectrum of p-benzosemiquinone anion (marked A) and e, the spectrum of tp-methoxyphenoxy radical (marked B) obtained after subtracting dfrom a. This figure illustrates the use of time-resolved resonance Raman spectroscopy to time-resolve the spectral overlap between transients decaying at different time scales.

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