Intra and Intermolecular Hydrogen Bonding

The melting and boiling points of carboxylic acids are much higher than would be expeeted on the basis of their molecular weights. The usual explanation is that they form weak intramolecular bonds. 

Display an electrostatic potential map iot acetic acid. Where are the most electron-rich sites Where are the most electron-poor sites Propose a structure for the dimer of acetic acid based on favorable electrostatic interactions between electron-rich and electron-poor sites. Compare your structure to that for acetic acid dimer. What is another name for the types of interactions that hold the two acetic acid molecules together (See also Chapter 2, Problem 2). 

The melting points of open-chain dicarboxylic acids, H20C(CH2)nC02H, alternate with length of the intervening methylene chain. 

One after the other, examine structures for octane-1,8-dioic acid, nonane-1,9-dioic acid djud decane-1,10-dioic acid. Is there any difference (in structure or conformation) between the diacids with lower and higher melting points Which, if any, of the acids adopt structures similar to that of acetic acid dimer Account for the variation in melting points of these three compounds. 

156 Chapter 10 Carboxylic Acid Derivatives. Nucleophilic Substitution 

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Instead, particular solvents interact rather specifically with the reactants and the transition state by intra- and intermolecular hydrogen bonding . ... 

The structure of the norbomylsiloxane 64 has been determined, but the x-ray data are of poor quality and do not permit a detailed picture of the hydrogen bonding to be made. However, as all of the hydroxy groups seem to point towards each other and there are broad absorptions at 3403 and 3243 cm-1 in the IR spectrum (KBr disk), it seems likely that both intra- and intermolecular hydrogen bonds are present (297). 

The differences in time-dependent adsorption behavior between 99% PVAC at 25° and 50°C demonstrate the influence of intra- and intermolecular hydrogen bonding in the adsorption process. The limiting surface pressure of the hydrophobic water-soluble polymer appears to be 33 mN/m, approximately 7 mN/m below that of commonly used surfactants. The rate of attainment of equilibrium surface pressure values is faster if there is uniformity of the hydrophobic segments among the repeating units of the macromolecule. 

In polypeptide blends, the balance of intra- and intermolecular hydrogen bond interactions in two kinds of polypeptide chains play an important role for the conformational stability and the blend miscibility. The observation of the 13 C NMR chemical shifts and relaxation times, and the two-dimensional... 

Pigment Red 177 [4051-63-2] has the chemical structure of 4,4 -diaminol,l -dianthraquinonyl and is prepared by intermolecular copper-catalyzed debromination of l-amino-4-bromoanthraquinone-2-sulfonic acid followed by desulfonation. It is the only known pigment with unsubstituted amino groups which are involved in both intra- and intermolecular hydrogen bonding (19). The bluish red pigment is used in plastics, industrial and automotive paints, and specialized inks (see Dyes, ANTHRAQUINONE). 

Figure 7. Structures of a-chitin with statistical hydrogen bonding network the shaded atoms represent half (06) oxygens oriented to form intra- and intermolecular hydrogen bonds ((a) ac projection (b) ab projection)...

An X-ray stmcture of diethyl 3,4-dihydroxythiophene-2,5-dicarboxylate 246 shows that the hydroxy groups lie in the plane of the molecules. This planarity leads to a larger number of potential intra- and intermolecular hydrogen bonds each hydroxy group is involved in one intra- and one intermolecular contact <2004AXCo338>. 

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