Phenolic proton

NMR The H NMR signals for the hydroxyl protons of phenols are often broad and their chemical shift like their acidity lies between alcohols and carboxylic acids The range is 8 4-12 with the exact chemical shift depending on the concentration the solvent and the temperature The phenolic proton m the H NMR spectrum shown for p cresol for example appears at 8 5 1 (Figure 24 4)... 

Coelenterazine (A) is oxidized into dehydrocoelenterazine (D) by MnC>2 in a mixed solvent of ethanol and ether (Inoue et al., 1977b). Dehydrocoelenterazine (C26H19O3N3) can be obtained as dark red crystals. It does not have the capability of chemiluminescence. The ultraviolet absorption spectrum (Fig. 5.6) shows its absorption maxima at 425 nm (e 24,400) and 536 nm (g 12,600) in ethanol. An addition of NaOH significantly increases the 536 nm peak at the expense of the 425 nm peak. Dehydrocoelenterazine can take a tautomeric structure of quinone type (not shown), in which the phenolic proton on the 2-substituent is shifted onto the N(7) of the imida-zopyrazinone ring. Dehydrocoelenterazine can be readily reduced to... 

Steadman, J., and Syage, J. A. (1991). Time-resolved studies of phenol proton transfer in clusters. 3. solvent structure and ion-pair formation. J. Phys. Chem. 95 10326-10331. 

The conjugate base of phenol is stabilized by resonance. This explains why phenolic protons are more acidic than typical alcoholic protons. 

The 2-(2 -hydroxyphenyl)benzotriazole derivatives, for example, are capable of forming intramolecular hydrogen bonds between a nitrogen atom on the triazole ring and the phenolic proton. This hydrogen bond facilitates the occurrence of a very rapid excited-state... 

The formation of (39) provides examples of a rearrangement where the rate is related to the acidity of the phenolic proton. 

INTRINSIC AND EXTRINSIC FLUORESCENCE. Intrinsic fluorescence refers to the fluorescence of the macromolecule itself, and in the case of proteins this typically involves emission from tyrosinyl and tryptopha-nyl residues, with the latter dominating if excitation is carried out at 280 nm. The distance for tyrosine-to-tryp-tophan resonance energy transfer is approximately 14 A, suggesting that this mode of tyrosine fluorescence quenching should occur efficiently in most proteins. Moreover, tyrosine fluorescence is quenched whenever nearby bases (such as carboxylate anions) accept the phenolic proton of tyrosine during the excited state lifetime. To examine tryptophan fluorescence only, one typically excites at 295 nm, where tyrosine weakly absorbs. [Note While the phenolate ion of tyrosine absorbs around 293 nm, its high pXa of 10-11 in proteins typically renders its concentration too low to be of practical concern.] The tryptophan emission is maximal at 340-350 nm, depending on the local environment around this intrinsic fluorophore. 

On the basis of the results cited above, we propose that the species in humic acids responsible for its paramagnetism is a charge transfer complex as described in Figure 11. The presence of an easily ionizable phenolic proton... 

The /wentfo-macrocyclic structure is also present in the solid state forms of some free ligands. [62] Overall, these are less planar than their 4-coordinate metal complexes, having a step conformation to reduce the repulsion between the central phenolic protons. Nevertheless, they are apparently well organized for complex formation and donor cavity sizes [63] give a good fit for divalent copper. [62]... 

The pKa value for pentazocine listed in general texts as 8. 6 (24) or 8.95 (2) is the tertiary amine protonation constant. Borg and Mikaelsson however have shown that two ionizations for pentazocine should be considered. First the pentazocinium ion loses the proton from the nitrogen and then the phenolic proton is lost at higher pH. This is pictured in Scheme 3 where two separate intermediates are possible the neutral pentazocine base (III) and a zwitterionic form (II). 

The large upfield shifts of 1.6 ppm for both phenolic protons which are located between rings B and C of the anthra-cycline ring chromophore demonstrates that the anthracycline ring intercalates into the nucleic acid duplex and experiences ring current contributions from adjacent base pairs. This in turn requires that anthracycline rings B and C overlap with adjacent base pairs at the intercalation site. 

The end product on treating phenol with D30+ simply has certain H atoms replaced by deuterium atoms. We say certain H atoms but exactly which ones The most acidic proton is the phenolic proton, the OH (pfCa about 10) this will rapidly be exchanged. The other protons that will be replaced will be the ones in the 2, 4, and 6 positions (that is, the ortho and para positions). Below is a reminder of the names we give to the positions around a benzene ring relative to any substituent. 

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