Hydrogen bond, carboxylic acid-pyridine

T.R. Shattock, K.K. Arora, P. Vishweshwar, M.J. Zaworotko, Hierarchy of supramolecular synthons persistent carboxylic acid pyridine hydrogen bonds in cocrystals that also contain a hydroxyl moiety, Cryst. Growth Des. 8 (2008) 4533M545. 

Figure 4 Macrocyclic complexes connected via carboxylic acid-pyridine hydrogen bonds.

Solvents with strong hydrogen bonding (alcohols, carboxylic acids, pyridine, water, glycols, amines)... 

Langner. R. Zundel, C. FTIR investigation of polarizable hydrogen bonds in carboxylic acid-pyridine complexes in... 

Figure 4 Rodlike mesogenic complexes 3-5 prepared by using carboxylic acid/pyridine hydrogen bonding.

Figure 2.1 Hydrogen-bonded units within the co-crystals (a) terephthalic acid pyridine (1 2) and (b) butanoic acid pyrazine (2 1). The carboxylic acid-pyridine hydrogen-bond motif forms a common theme throughout this chapter.

In the course of this study, the authors determined /Lvalues for dibenzyl, methyl phenyl, methyl p-nitrophenyl, di-p-tolyl, di-isopropyl and tetramethylene sulphoxides and for diethyl, dipropyl and dibutyl sulphites. The /Lscales are applied to the various reactions or the spectral measurements. The /Lscales have been divided into either family-dependent (FD) types, which means two or more compounds can share the same /Lscale, family-independent (FI) types. Consequently, a variety of /Lscales are now available for various families of the bases, including 29 aldehydes and ketones, 17 carboxylic amides and ureas, 14 carboxylic acids esters, 4 acyl halides, 5 nitriles, 10 ethers, 16 phosphine oxides, 12 sulphinyl compounds, 15 pyridines and pyrimidines, 16 sp3 hybridized amines and 10 alcohols. The enthalpies of formation of the hydrogen bond of 4-fluorophenol with both sulphoxides and phosphine oxides and related derivatives fit the empirical equation 18, where the standard deviation is y = 0.983. Several averaged scales are shown in Table 1588. 

Hydrogen bond donor solvents are simply those containing a hydrogen atom bound to an electronegative atom. These are often referred to as protic solvents, and the class includes water, carboxylic acids, alcohols and amines. For chemical reactions that involve the use of easily hydrolysed or solvolysed compounds, such as AICI3, it is important to avoid protic solvents. Hydrogen bond acceptors are solvents that have a lone pair available for donation, and include acetonitrile, pyridine and acetone. Kamlet-Taft a and ft parameters are solvatochromic measurements of the HBD and HBA properties of solvents, i.e. acidity and basicity, respectively [24], These measurements use the solvatochromic probe molecules V, V-die lliy I -4-n i in tan iline, which acts as a HBA, and 4-nitroaniline, which is a HBA and a HBD (Figure 1.17). 

The crystal structure of CdL py -py (LH = 4-hydroxybenzoic acid) has been reported, and the metal shown to be in an octahedral environment 786,787 one of the carboxylate anions is bidentate, but the other is monodentate and hydrogen-bonded to one of the pyridine molecules. The remaining three pyridine molecules are coordinated to the metal. 

The low value for oS30 undoubtedly arises from intramolecular hydrogen bonding stabilizing the neutral form of the acid (4), a circumstance also occurring in the pyridine-2-carboxylic and -2-hydroxamic acids as well as 2-hydroxypyridine. 

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