CHM136H1 Lecture Notes - Alkali Metal, Carboxylic Acid, Hydrogen Bond

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Published on 28 Sep 2012
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Carboxylic acid are similar in some respects to both ketones and alcohols
sp2-hybridized
planar with C-C=O and O=C-O
bond angle is about 120 degrees
carboxylic acids are strongly associated because of hydrogen bonding
higher boiling point than the corresponding alcohols
most exist as cyclic dimers held together by two hydrogen bonds
acidic
6+ carbons are only slightly soluble in water
but the alkali metal salts of carboxylic acid are often highly water soluble
purify an acid by extracting its salt into aqueous base, then reacidifying and extracting the pure acid
back into an organic solvent
dissociate slightly
about E-4/-5 <-meaning that it is about 0.1% of the molecules in a 0.1M solution are dissociated
An alcohol dissociates to give an alkoxide ion, in which the negative charge is localized on a single
electronegative atom, however, gives a carboxylate ion, in which the negative charge is delocalized
over two equivalent oxygen atoms.
carboxylate ion is a stabilized resonance hybrid of two equivalent structures.
Since carboxylate ion is more stable than an alkoxide ion, it is lower in energy and more favored in
the dissociation equilibrium.
electrostatic potential map of the format ion also shows how the negative charge (red ) is spread
equally over both oxygen