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Acids and Bases

Article ID: 26
Last updated: 25 Jan, 2012
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In Organic Chemistry, both acids and bases are usually thought of by their ability to act as acids. The pKa unit is the most common way to compare acidic (even if very poorly acidic) protons on different molecules. Two molecules that are more than 3 pKa units apart will result in almost complete dissociation of the stronger acid (lower pKa).  Remember that acidity and basicity are based on the same reversible chemical reaction (but looking at it from opposite sides). In the following generic example the base, B, removes a proton from the acid, H-A:

 

 

There are three definitions of acids and bases that Organic Chemists use that you should be familiar with: the Arrenhius, Bronsted, and Lewis definitions, which are summarized below (it is crucial to commit this table to memory):

 

 

Acids

Bases

Arrenhius

Ionize to give H+ in H2O

Ionize to give HO- in H2O

Bronsted-Lowry

A proton donor

A proton acceptor

Lewis

An electron pair acceptor

An electron pair donor

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Use arrows to show the mechanism and products formed when the Lewis basic molecule below is reacted with boron trifluoride?

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Department of Chemistry & Chemical Biology