Carboxylate anion structure

Xanthine anions structure, 5, 509 Xanthine-8-carboxylic acid synthesis, 3, 308, 322 Xanthine oxidase... 

Fig. 1 a Crystal structure of the carboxylate anion portion of the (R)-(+)-l-phenylethyl-amine salt of keto-acid 37a before irradiation, and b after 70% conversion to the corresponding cyclobutanol (ionic chiral auxiliary not shown)... 

This generalized structure was mimicked by a very simplified artificial molecule 1. The hydrophilic core part 2 was substituted simply by an oligoether carboxylate anion. The carboxylate may act as the polar ionic head group outside the membrane and the ether part of the molecule may be located in the interior part of the membrane to make an ion-conducting pathway. The molecular lengths were adjusted to fit the lipid monolayer in an extended or a helical conformation, with n being 2 or 3 in 1. The hydrophobic exterior was substituted by dioctadecyldimethyl-ammonium cation, which was ion-paired with the carboxylate. 

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 stabilization energy of the carboxylate anion is substantially greater than that of the acid, because the anion is a resonance hybrid of two energetically equivalent structures, 2a and 2b, whereas the acid is represented by a hybrid of nonequivalent structures, 1a through 1c ... 

The rules for resonance stress that the greatest stabilization is expected when the contributing structures are equivalent (Section 6-5B). Therefore we can conclude that the resonance energy of a carboxylate anion should be... 

Nitro compounds are a very important class of nitrogen derivatives. The nitro group, —N02, like the carboxylate anion, is a hybrid of two equivalent resonance structures ... 

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