Organic and biochemistry Assistancce Lecturer Amjad Ahmed Jumaa  Basicity of aromatic amines.  Concept the carbanions.  Methods of generated of the carbanions.  Reactions involving carbanions. 1

Basicity of aromatic amines:  The electron-releasing groups increases the basicity of aromatic amines, because the unshared-electron pair are more available to the proton and thus more stabilize the cation. In contract, the electron-withdrawing groups decrease the basicity of the aromatic amines because the unshared-electron pairs are unavailable to the proton and thus less stabilize the cation. Basicity of aromatic amines:  The electron-releasing groups increases the basicity of aromatic amines, because the unshared-electron pair are more available to the proton and thus more stabilize the cation. In contract, the electron-withdrawing groups decrease the basicity of the aromatic amines because the unshared-electron pairs are unavailable to the proton and thus less stabilize the cation.

Problem: which of the following amines are more basic? Ethyl amine; diethyl amine; aniline; p-nitroaniline. Solution: Diethyl amine > Ethyl amine > aniline > p-nitroaniline. Problem: arrange the following aromatic amines according in increase in basicity: p-chloroaniline; m-methoxyaniline; p-nitroaniline; p- aminoaniline. Solution: p-aminoaniline > m-methoxyaniline > p-chloroaniline > p- nitroaniline. Solution: Diethyl amine > Ethyl amine > aniline > p-nitroaniline. Problem: arrange the following aromatic amines according in increase in basicity: p-chloroaniline; m-methoxyaniline; p-nitroaniline; p- aminoaniline. Solution: p-aminoaniline > m-methoxyaniline > p-chloroaniline > p- nitroaniline.

 Some important organic chemical reactions:  Concepts of the carbanions: The carbanion is the carbon atom that bears a negative charge.  Some important organic chemical reactions:  Concepts of the carbanions: The carbanion is the carbon atom that bears a negative charge.  Methods of generated of the carbanions:  One of the methods to obtain carbanions is the ionization of a α-hydrogen which attached to the α-carbon (C-1) in the carbonyl compounds (aldehydes and ketones). Ionization achieved by a base.

o The carbanion (I) is a resonance hybrid of two structures (II) and (III).  Also the carbonyl group affects the acidity of α-hydrogen in just the way it affects the acidity of carboxylic acid; by helping to accommodate the negative charge of the anion:

 The carbonyl group undergoes nucleophilic attack this is due to the ability of oxygen to accommodate the negative charge that develops as a result of the attack:

 Reactions involving carbanions:  The carbanions are highly basic. In their reactions they behave as nucleophiles. They can attack carbon to form carbon-carbon bonds.  Reactions involving carbanions:  The carbanions are highly basic. In their reactions they behave as nucleophiles. They can attack carbon to form carbon-carbon bonds. Halogenation of ketones:

Example: Problem: in the reaction of the acetone with bromide gas (Br 2 ) in the basic medium (OH - ); expect the product. Solution:

Follow problem: write balanced equations, naming all organic products for the chlorination in the basic medium for the following compounds. 1- Phenyl acetaldehyde 2- methyl ethyl ketone 3- acetophenone. 4- (3-pentanone). Follow problem: write balanced equations, naming all organic products for the chlorination in the basic medium for the following compounds. 1- Phenyl acetaldehyde 2- methyl ethyl ketone 3- acetophenone. 4- (3-pentanone).