Paris D. Svoronos

CRC handbook of fundamental spectroscopic correlation charts

Ultraviolet-Visible Spectrophotometry Correlation Charts for Ultraviolet-Visible Spectrophotometry Woodwards Rules for Bathochromic Shifts Solvents for Ultraviolet Spectrophotometry Transmittance-Absorbance Conversion Calibration of Ultraviolet-Visible Spectrophotometers Infrared Spectrophotometry Infrared Absorption Correlation Charts Legend for Correlation Charts Aromatic Substitution Bands Carbonyl Absorptions Near-Infrared Absorptions Inorganic Group Absorptions Useful Solvents for Infrared Spectrophotometry Acetonitrile, CH3CN Benzene, C6H6 Bromoform, CHBr3 Carbon Disulfide, CS2 Carbon Tetrachloride, CCl4 Chloroform, CHCl3 Cyclohexane, C6 H12 Dimethyl Sulfoxide, (CH3)2SO 1,4-Dioxane, OCH2CH2OCH2CH2 Ethyl Acetate, CH3COOC2H5 n-Hexane, CH3(CH2)4CH3 Isopropanol, (CH3)2CHOH Methyl Ethyl Ketone, CH3COC2H5 n-Octane, CH3(CH2)6CH3 Tetrahydrofuran, CH2(CH2)2CH2O Toluene, CH3C6H5 Paraffin Oil Fluorolube(TM), Polytrifluorochloroethylene, [-C2ClF3-] Polystyrene Wavenumber Calibration Wavelength-Wavenumber Conversion Table Diagnostic Spectra Nuclear Magnetic Resonance Chemical-Shift Ranges of Some Nuclei Reference Standards for Selected Nuclei 1H and 13C Chemical Shifts of Useful NMR Solvents Proton-NMR Absorptions of Major Functional Groups Some Useful 1H Coupling Constants Additivity Rules in 13C -NMR Correlation Tables 13C -NMR Absorptions of Major Functional Groups 15N Chemical Shifts for Common Standards 15N Chemical Shifts of Major Functional Groups Spin-Spin Coupling to 15N 19F Chemical-Shift Ranges 19F Chemical-Shift Ranges of Some Fluorine-Containing Compounds Fluorine Coupling Constants 31P-NMR Absorptions of Representative Compounds 29Si-NMR Absorptions of Major Chemical Families 119Sn-NMR Absorptions of Major Chemical Families Mass Spectrometry Natural Abundance of Important Isotopes Rules for Determination of Molecular Formula Neutral Moieties Ejected from Substituted Benzene Ring Compounds Order of Fragmentation Initiated by the Presence of a Substituent on a Benzene Ring Chlorine-Bromine Combination Isotope Intensities Reference Compounds Under Electron-Impact Conditions in Mass Spectrometry Major Reference Masses in the Spectrum of Heptacosafluorotributylamine (Perfluorotributylamine) Common Fragmentation Patterns of Families of Organic Compounds Common Fragments Lost Important Peaks in the Mass Spectra of Common Solvents Detection of Leaks in Mass Spectrometer Systems Laboratory Safety Major Chemical Incompatibilities Abbreviations Used in the Assessment and Presentation of Laboratory Hazards Characteristics of Chemical-Resistant Materials Selection of Protective Laboratory Garments Protective Clothing Levels Selection of Laboratory Gloves Selection of Respirator Cartridges and Filters Standard CGA Fittings for Compressed-Gas Cylinders Gas-Cylinder-Stamped Markings Unit Conversions and Physical Constants Unit Conversions Recommended Values of Selected Physical Constants Subject Index Chemical Compound Index

Effect of various acids at different concentrations on the pinacol rearrangement

The acid catalyzed pinacol–pinacolone rearrangement has been well studied for a long time 1 and has served as a standard topic in most undergraduate organic textbooks. With benzopinacol as the diol, tetraphenylethylene oxide was also produced 2 in addition to the expected benzopinacolone. Several non-dehydrative pinacol rearrangements with various Lewis acids have also been reported. 3 More recently, similar rearrangements were observed in the presence of aminium salts. 4 A theoretical study of the mechanism that involves both stepwise and concerted reaction paths has been described by Nakamura and Osamura. 5 Although, the classical pinacol to pinacolone rearrangement is well documented, we were intrigued by some reports 1j that under certain acidic conditions, 2,3-dimethyl-1,3-butadiene becomes the major product in the reaction. This suggests a shift in the mechanistic pathway (Scheme 1) leading to the preferred formation of 2. In order to understand the competing reaction pathways, we evaluated the effect of changing the concentration of various acids as well as the effect of added conjugate base. Our results indicate that although the 1,2-migration is the preferred pathway, the alternative route also competes leading to products 2 and 3 (Scheme 1). The change in the ratio of rearrangement to elimination products described in this work is in agreement with the results obtained in the pinacol–pinacolone rearrangement of 2,3-di-(3-pyridyl)-2,3-butanediol in sulfuric acid and the effect of added water. 6

Chapter 6 Chemistry of Melanins

Publisher Summary This chapter provides a concise, yet comprehensive and up-to-date overview of the field of melanins, with particular emphasis on the chemical, physical, and biosynthetic aspects of these important and ubiquitous pigments. Tyrosinase is known to catalyze the biosynthesis of not only black but also brown, yellow, reddish brown, and carrot-red pigments. Melanin pigmentation is mainly determined by two chemically distinct but biogenetically related types of pigments. One of them is the dark, insoluble eumelanins that are produced from the tyrosinase-catalyzed oxidation of tyrosine, and the other is the alkalisoluble phaeomelanins that originate from an altered eumelanin pathway through the intervention of cysteine. Evidence suggests that certain heavy metal ions, commonly found in pigmented tissues, play an important role in melanogenesis. Of particular interest is the finding that copper and, to a lesser degree, zinc, cobalt, and iron have the ability to catalyze the rearrangement of dopachrome to 5,6-dihydroxyindole(s), which is a key regulatory step in the biosynthesis of eumelanins.