Wikibooks: Structural Biochemistry/Organic Chemistry/Organic Functional Group/Carboxyl

• Format: Book
• Language: English
• Subjects: Carbonic acid
• Online Access: https://en.wikibooks.org/wiki/Structural_Biochemistry/Organic_Chemistry/Organic_Functional_Group/Carboxyl

=Introduction= A carboxyl group consists of a carbon double bonded to an oxygen and also bonded to a OH group. Compounds with carboxyl groups are called carboxylic acids or organic acids. The carboxyl group can act as an acid when by donating a proton (H + ) to a solution and becoming ionized. Under biological conditions at pH~7 carboxyl groups are usually deprotonated meaning they lose a H + and become negatively charged. An example of a carboxyl group in the body would be carbonic acid formed from the hydration of a carbon dioxide. Under biological conditions carbonic acid usually dissociates into bicarbonate ion. =Properties= Carboxyl groups have an electronegative oxygen atom double bonded to a carbon atom. This carbon oxygen bond is very polar and the fact that its a double bond increases the polarity of the bond. As a result of the polarity compounds containing carboxyl groups usually have higher melting points boiling points and have hydrophilic centers. Moreover the higher melting point and higher boiling point can be attributed to the fact that they can form hydrogen bonds both in the liquid and solid state. [[Fatty acids]] are examples of compounds that have hydrophilic centers due to their carboxyl groups. Also carboxyl groups especially when present in molecules with a low molecular weight tend to be highly volatile and therefore tend to have strong odors. The pKa of carboxyl groups usually range from 4 5. =Nomenclature= In naming organic molecules with multiple functional groups the carboxyl group takes precedence in naming over any other functional group. Therefore when naming a molecule such as an alkane that contains a carboxyl group the e on the alkane is replaced by oic acid. Also when numbering the chain of the organic molecule that contains a carboxyl group the carboxy carbon is labeled as the number 1 carbon. Molecules with two carboxyl groups would use instead the dioic suffix. =Bonding= The polarity of the carbon oxygen bond makes the carbon very susceptible to nucleophilic attack. Upon ...