Carboxylic acid covalent structure

The transformation of the hydrophobic periphery composed of bromo substituents into a hydrophilic wrapping of carboxylic acid functions was achieved by reacting 31 with (i) n-butyllithium and (ii) carbon dioxide. The polymer-analogous transformation provides water soluble, amphiphilic derivatives of 31 which constitute useful covalently bonded unimolecular models for micellar structures. 

Amino acids and the structure of the polypeptide chain. Polypeptides are composed of L-amino acids covalently linked together in a sequential manner to form linear chains, (a) The generalized structure of the amino acid. The zwitterion form, in which the amino group and the carboxyl group are ionized, is strongly favored. (b) Structures of some of the R groups found for different amino acids, (c) Two amino acids become covalently linked by a peptide bond, and water is lost, (d) Repeated peptide bond formation generates a polypeptide chain, which is the major component of all proteins. 

There are many kinds of capsules but few have the capacity to position co-guests in predictable orientations. We used the ability of 1.24.1 to do so, and applied it to evaluate hydrogen-bonding interactions between boronic acids, carboxylic acids, and primary amides [52], The phenyl boronic acids are useful as components of covalently self-assembled systems [53], and we found that the p-methyl, methoxy, ethyl, and isopropyl derivatives all fit as symmetrical dimers inside I.24.I. The structure of the boronic acid dimer has been debated but a recent theoretical study found the doubly hydrogen-bonded exo/endo conformer (Fig. 10) to be lowest in... 

The functional groups of heparin suitable for formation of a covalent bond include the alcohol, carboxylic acid, and amino groups. The structure of heparin is shown in Figure 1. The amino groups readily react with... 

The use of transition metals or transition metal clusters to act as nodes for the modular self-assembly of diamondoid networks that are sustained by coordinate covalent bonds is also well established. Such architectures are of more than aesthetic appeal. Indeed, such structures have resulted in a class of compound with very interesting bulk and functional properties. Metal-organic diamondoid structures in which the spacer moiety has no center of inversion are predisposed to generate polar networks since there would not be any inherent center of inversion. Pyridine-4-carboxylic acid is such a ligand and bis(isonicotinato)zinc exists as a three-fold diamondoid structure that is thermally stable and inherently polar.33... 

A different type of crown ether used to separate enantiomers is the one derived from 18-crown-6 tetracarboxylic acid, covalently immobilized on silica gel via reaction between 18-crown-6 tetracarboxylic acid and amino propyl silica gel [76]. The structure of 18-crown-6 tetra carboxylic is presented in Figure 22-18 [77]. The enantioselectivity on this chiral phase is improved by the addition of triethylamine into the mobile phase and operating at high methanol concentrations however, enhanced selectivity may come at the expense of greatly increased retention times [78]. 

In contrast to this equal propensity toward formation of a H-bond, there is a definite preference for a proton to locate on the syn side when coming much closer and forming a covalent bond. That is, the syn conformer of RCOOH is more stable than the anti structure by about 5 kcal/mol in the gas phase. If this is the case, why then is there so little apparent pK difference between the syn and anti structures The answer to this question resides in solvation phenomena. The presence of the polarizable medium preferentially stabilizes the anti conformer of the carboxylic acid due to its higher dipole moment. 

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