Science Essays Carboxylic acids (RCO2H) are one of t

Carboxylic acids (RCO2H) are one of the most abundant organic compounds in nature. Their common structural feature is that they contain an acyl group bonded to an electronegative atom or substituent that acts as a leaving group in substitution reactions. They consist of acid halides (RCOX), acid anhydrides (RCO2COR'), amides (RCONH2), esters (RCO2R), and nitriles R-C=N), with the active group replacing the -OH group of the acid. Carboxylic acids are weaker than mineral acids (e.g. HCl), but more acidic than alcohols because carboxylate anions are more stable than alkoxide ions. They usually have a pKa around 5. This is because in a carboxylate ion, the negative charge is shared by both oxygen atoms, leaving them stabilized in resonance hybrid structures, whereas in the alkoxide, the negative charge is localized in one oxygen atom. Because acid dissociation is an equilibrium process, the presence of an electron-withdrawing group favors dissociation and increased acidity. For instance chloracetic acid, an acid halide, is stronger than acetic acid by a factor of 75, and dichloracetic acid is stronger by 3000 times.

The chemistry of all carboxylic acid derivatives is similar and there is a single dominant reaction type known as the nucleophilic acyl substitution reaction. This occurs by the addition of as nucelophile to the polar carbonyl group of the acid derivative. This is followed by expulsion of the leaving group. The most important nucleophiles whic

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ed by reaction with alkyl halides. Primary and secondary amines can also be alkylated by nucleophilic acyl substitution reactions with acid chlorides. Cyclic organic compounds are carbocycles or heterocycles, depending on whether they contain only carbon atoms or other atoms as well. Heterocyclic amines have the same chemistry as their open chain counterparts. Pyrrole is a 5-membered aromatic heterocycle and pyridine is a 6-membered aromatic heterocycle analog of benzene. Fused-ring heterocycles have a benzene ring and a heterocyclic ring sharing a common bond. Naturally occurring plant amines are known as alkaloids and are the source of many drugs, e.g. reserpine, ephedrine, atropine and cocaine. Chapter 13 Three main spectroscopic techniques are used to determine the structure of organic molecules: Infrared spectroscopy is used to determine what functional groups are present; Ultraviolet spectroscopy is used to determine if a conjugated pi electron system is present; and Nuclear Magnetic Resonance spectroscopy is used to look at the carbon-hydrogen framework of the molecule. When infrared (IR) energy is used to irradiate a molecule, frequencies of light which correspond to the energies of molecular stretching and bon

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