Methyl orange resonance

Another simple example of the connexion between resonance and colour is shown by the indicator methyl orange, and at the same time the mode of action of the azo group chromophore is demonstrated. In the presence of alkali it exists in the form (12),... 

Nuclear Magnetic Resonance Spectra of Cyclodextrin Monomers, Derivatives and their Complexes with Methyl Orange... 

Methyl-4-phenyl-l,2,5-thiadiazole 1,1-dioxide 21 suffers proton abstraction in basic nonaqueous media to give a resonance stabilized anion 43, neutralization of which using anhydrous TFA gives the orange tautomer 4-methylene-3-phenyl-l,2,5-thiadiazoline 1,1-dioxide 44 (Scheme 3) <2001JP0217>. The tautomeric equilibrium is practically displaced toward 21 in acetonitrile and toward 44 in DMF. 

Tris(tri-o-toIyI phosphite)nickel(O) is a bright red-orange solid which decomposes above ca. 125-140°. The 407-nm. peak has e = 5.0 x 103 cm.-1 M 1 and the 450-nm. shoulder has e = 3.7 x 103 cm.-1 M-1. The n.m.r. signal of the methyl hydrogens in free tri-o-tolyl phosphite is at 2.11 p.p.m. down field from internal tetramethylsilane in benzene solution, while the methyl resonance of coordinated tri-o-tolyl phosphite is only 1.96 p.p.m. down field. 

Fig. 11 Sequence-specific resonance assignments of two proteins obtained with the APSY CA-CB-CM strategy [51], Data is shown for two proteins, the 15-kDa protein A (panels a-c) and the 22-kDa protein kRas (panels d-f). Selected sample parameters are indicated. The amide resonance assignments are shown in blue on 2D [ N, H]-HSQC spectra (panels a and d), with their central regions shown enlarged (panels b and e). The methyl group assignments are indicated in orange on 2D [ C, H]-HMQC spectra (panels c and f). Adapted with permission from [51]...

Carbon stable isotope ratio (CSIR) analysis of sugar utilizing an isotope ratio mass spectrometer (IRMS) is routinely used to detect the addition of cane sugar and corn syrup to most juices with the exception of pineapple. The inability of CSIR analysis to detect beet sugar in orange and apple juices because of metabolic similarities between adulterant and authentic products has required alternative methods, e.g., combination of IRMS and nuclear magnetic resonance (NMR) spectroscopy. The method requires the determination of five isotope ratios after fermentation of the juice the H/ H and iSq/ISo ratios of the fermentation water plus the total C/ C and H/ H ratios on the methyl and methylenic groups of the alcoholic distillate. 

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