Structural and Electronic Effects Acids and Bases
Structural and electronic effects
Acids and Bases
Acknowledgement
Some material have been sourced from the following websites and books Reference
• http://facstaff.gpc.edu/~matteya/organicppt/Ch2.ppt • http://atom.chem.wwu.edu/dept/facstaff/pavia/351pavia.html • www.fccj.us/chem1212/powerpoint/Ch17_Lewis_B.ppt • CH102 Course book
• Organic Chemistry 7th Edition by John McMurry
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Acids & Base Definitions
Definition #3 – Lewis
• Lewis acid - a substance that accepts an electron pair
• All BrØnsted-Lowry acids are also Lewis acids, but the reverse is not necessarily true. o Any species that is electron deficient and capable of accepting an electron pair is also a Lewis acid. • Common examples of Lewis acids (which are not BrØnstedLowry acids) include BF3 and AlCl3. These compounds contain elements in group 3A of the periodic table that can accept an electron pair because they do not have filled valence shells of electrons.
• Lewis base - a substance that donates an electron pair
3 4
• In a Lewis acid-base reaction, a Lewis base donates an electron pair to a Lewis acid. • One bond is formed and no bonds are broken. This is illustrated in the reaction of BF3 with H2O. H2O donates an electron pair to BF3 to form a new bond.
pKa’s AND ACID STRENGTH pKa - An alternative to Ka to describe acid strength. (A concise way to state the strength of an acid.)
electron pair is not removed from the Lewis base. Instead, it is donated to an atom of the Lewis acid and one new covalent bond is formed.
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1
Acid Strength and pKa
• Acid strength is the tendency of an acid to donate a proton. • The more readily a compound donates a proton, the stronger an acid it is. • Acidity is measured by an equilibrium constant. • When a Brønsted-Lowry acid H—A is dissolved in water, an acid-base reaction occurs, and an equilibrium constant can be written for the reaction.
Because the concentration of the solvent H2O is essentially constant, the equation can be rearranged and a new
Acids and Bases
Acknowledgement
Some material have been sourced from the following websites and books Reference
• http://facstaff.gpc.edu/~matteya/organicppt/Ch2.ppt • http://atom.chem.wwu.edu/dept/facstaff/pavia/351pavia.html • www.fccj.us/chem1212/powerpoint/Ch17_Lewis_B.ppt • CH102 Course book
• Organic Chemistry 7th Edition by John McMurry
2
Acids & Base Definitions
Definition #3 – Lewis
• Lewis acid - a substance that accepts an electron pair
• All BrØnsted-Lowry acids are also Lewis acids, but the reverse is not necessarily true. o Any species that is electron deficient and capable of accepting an electron pair is also a Lewis acid. • Common examples of Lewis acids (which are not BrØnstedLowry acids) include BF3 and AlCl3. These compounds contain elements in group 3A of the periodic table that can accept an electron pair because they do not have filled valence shells of electrons.
• Lewis base - a substance that donates an electron pair
3 4
• In a Lewis acid-base reaction, a Lewis base donates an electron pair to a Lewis acid. • One bond is formed and no bonds are broken. This is illustrated in the reaction of BF3 with H2O. H2O donates an electron pair to BF3 to form a new bond.
pKa’s AND ACID STRENGTH pKa - An alternative to Ka to describe acid strength. (A concise way to state the strength of an acid.)
electron pair is not removed from the Lewis base. Instead, it is donated to an atom of the Lewis acid and one new covalent bond is formed.
5
1
Acid Strength and pKa
• Acid strength is the tendency of an acid to donate a proton. • The more readily a compound donates a proton, the stronger an acid it is. • Acidity is measured by an equilibrium constant. • When a Brønsted-Lowry acid H—A is dissolved in water, an acid-base reaction occurs, and an equilibrium constant can be written for the reaction.
Because the concentration of the solvent H2O is essentially constant, the equation can be rearranged and a new