Carboxylic acids chemical shifts

Kubicki JD, Blake GA, Apitz SE (1999a) Molecular models of benzene and selected PAHs in the gas, aqueous, and adsorbed states. Env Toxicol Chem 18 1656-1662 Kubicki JD, Sykes D, Apitz SE (1999b) Ab initio calculation of aqueous aluminmn and aluminum-carboxylate NMR chemical shifts. J Phys Chem A 103 903-915 Kubicki JD, Itoh MJ, Schroeter LM, Nguyen BN, Apitz SE (1999c) Attenuated total reflectance Fourier-transform infrared spectroscopy of carboxylic acids adsoibed onto mineral surfaces. Geochim Cosmochim Acta 63 2709-2725... 

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)... 

The impact of a carboxylic acid function upon the chemical shift of a CF2H group is almost indistinguishable from the impact of a ketone, whereas secondary CF2 groups next to an acid or ester function are slightly deshielded relative to those next to a ketone or aldehyde (Scheme 4.35). 

With regard to carboxylic derivatives, there is generally little difference in chemical shift among the various trifluoroacetic acid derivatives, as exemplified by the examples in Scheme 5.25. Also, the effect of moving the CF3 farther from the carboxylic acid function is similar... 

Shi et al.71 have assigned the backbone and side-chain chemical shifts for 103 of 238 residues of proteorhodopsin using solid state NMR spectroscopy. Analysis of the chemical shifts has allowed determination of protonation states of several carboxylic acids as well as boundaries and distortions of trans-membrane a-helices and secondary structure elements in the loops. It has been shown that internal Asp227, making a part of the counterion, is ionised, while Glul42 located close to the extracellular surface is neutral. 

The synthesis of lanthanide chemical shift reagents has been the objective of many groups owing to their effect on NMR spectra simplification. A drawback of the commonly used reagents is their sensitivity to water or acids. Tris(tetraphenylimido diphosphinatojpraseodymium [Pr(tpip)3] has been developed as a CSR for the analysis of carboxylic acids.17 Furthermore, it has been found that dinuclear dicarboxylate complexes can be obtained through reactions with ammonium or potassium salts of carboxylic acids, and these compounds can be used to determine the enantiomer composition of carboxylic acids.18... 

Methods for the A-acylation of similar heterocycles, such as simple thiazolidinethiones, have been reported since 1977, namely acyl chlorides in miscellaneous conditions,586 or carboxylic acids under DCC-activation.60,61 However the easiest and most effective method involves acyl chlorides or carboxylic anhydrides in the presence of an amine.47 Applying that procedure on carbohydrate scaffolds Rollin and co-workers62 reported the synthesis of diverse /V-acylated OZTs. The reactions were performed with good yields and the /V-selective acylation was ascertained by NMR— namely the thiocarbonyl 13C chemical shift (Scheme 41). Thanks to the dual nature of the carbanion drifting in the reaction,596 60 no competitive formation of the thioester, as mentioned by Plusquellec el al. in the case of benzothiazole, was observed. 

OH protons in alcohols, phenols or carboxylic acids -SH protons in thiols -NH protons in amines or amides do not have reliable chemical shift ranges (see page 49). 

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