Organic Functional Groups

Identification and Properties of Functional Groups

Organic molecules are classified by the functional groups they contain, which determine their chemical reactivity and physical properties.

• Alcohol: Contains a hydroxyl (-OH) group attached to a carbon atom.

• Amine: Contains a nitrogen atom bonded to one or more alkyl or aryl groups.

• Amide: Contains a carbonyl group (C=O) bonded to a nitrogen atom.

• Carboxylic acid: Contains a carboxyl group (-COOH).

Example: The structure of thienamycin contains alcohol, amine, amide, and carboxylic acid groups. Identifying these groups is essential for understanding the molecule's reactivity.

Solubility of Organic Compounds

Factors Affecting Solubility in Water

The solubility of organic compounds in water depends on the presence of polar functional groups and the ability to form hydrogen bonds.

• Alcohols and carboxylic acids are generally more soluble due to their ability to hydrogen bond with water.

• Increasing the number of hydroxyl (-OH) groups increases solubility.

Example: HOCH2CH2OH (ethylene glycol) is more soluble than CH3CH2OH (ethanol) due to two hydroxyl groups.

Oxidation of Alcohols

Types of Alcohols and Their Oxidation Products

Alcohols are classified as primary, secondary, or tertiary based on the number of alkyl groups attached to the carbon bearing the hydroxyl group.

• Primary alcohols oxidize to aldehydes, then to carboxylic acids.

• Secondary alcohols oxidize to ketones.

• Tertiary alcohols generally do not undergo oxidation under mild conditions.

Equation:

Organic Nomenclature

IUPAC Naming of Organic Compounds

The International Union of Pure and Applied Chemistry (IUPAC) system provides rules for naming organic molecules based on their structure.

• Identify the longest carbon chain containing the principal functional group.

• Number the chain to give the lowest possible numbers to substituents.

• Name and number substituents as prefixes.

• Assign the appropriate suffix for the functional group (e.g., -ol for alcohols, -one for ketones, -oic acid for carboxylic acids).

Example: The IUPAC name for dimethyl ketone is propanone (commonly known as acetone).

Common Organic Molecules

Recognizing and Naming Small Molecules

Students should be familiar with the structures and names of common organic molecules, including:

• Formic acid, acetic acid, propionic acid, butyric acid

• MEK (methyl ethyl ketone), acetone

• Diethyl ether, ethanol, methanol

• Glycine, alanine, acetaldehyde, formaldehyde

Example: Butanoic acid is a four-carbon carboxylic acid with the formula CH3CH2CH2COOH.

Acidity and Acid Strength

Comparing Acid Strengths Using Ka Values

The strength of an acid is measured by its acid dissociation constant (Ka). A higher Ka value indicates a stronger acid.

• Strong acids have higher Ka values and lower pKa values.

• Weak acids have lower Ka values and higher pKa values.

Example Table:

Additional info: Trichloroacetic acid is the strongest acid in the list due to its highest Ka value.

Organic Reactions

Major Types of Organic Reactions

Organic compounds undergo various reactions, including oxidation, reduction, substitution, and elimination.

• Dehydration of alcohols: Produces alkenes via elimination of water.

• Oxidation of alcohols: Converts alcohols to aldehydes, ketones, or carboxylic acids.

• Hydrolysis of esters: Produces alcohol and carboxylic acid (acid hydrolysis) or alcohol and carboxylate ion (base hydrolysis).

Equation:

Amines and Amides

Classification and Reactions of Amines

Amines are classified as primary (1°), secondary (2°), or tertiary (3°) based on the number of alkyl groups attached to the nitrogen atom.

• Primary amine: One alkyl group attached to nitrogen.

• Secondary amine: Two alkyl groups attached.

• Tertiary amine: Three alkyl groups attached.

• Amines can form intermolecular hydrogen bonds, especially primary and secondary amines.

Example: Ethyl phenyl amine is a primary amine with an ethyl and a phenyl group attached to nitrogen.

Buffers and pH

Choosing Buffers for Specific pH Values

Buffers are solutions that resist changes in pH upon addition of small amounts of acid or base. The best buffer for a given pH is one whose pKa is close to the desired pH.

• Formic Acid: pKa = 3.74

• Acetic Acid: pKa = 4.74

• Phosphoric Acid: pKa = 2.15

• Ascorbic Acid: pKa = 4.10

• Trichloroacetic Acid: pKa = 0.64

Example: For a pH 4.0 buffer, ascorbic acid (pKa = 4.10) is most suitable.

Phosphate Esters

Preparation and Properties

Phosphate esters are formed by the reaction of phosphoric acid with alcohols, carboxylic acids, or amines.

• Phosphoric acid + alcohol → phosphate ester

• Phosphoric acid + amine → phosphate amide

Example: Phosphate esters are important in biochemistry, such as in ATP and DNA.

Summary Table: Functional Groups and Their Properties

Additional info:

• Students should be able to predict products of reactions such as oxidation, hydrolysis, and elimination.

• Practice drawing structures and naming compounds using IUPAC rules.

• Understand the relationship between structure and properties, such as solubility and acidity.