Question

Draw formulas for the first five members of each homologous series beginning with the following compounds. (a) \(\mathrm{H}-\mathrm{COOH}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}\). (c) \(\mathrm{H}-\mathrm{CH}=\mathrm{CH}_{2}\)

Short answer

Identify the functional group and draw formulas based on the homologous series, starting with the given compound.

Step-by-step solution

Identify the Homologous Series for Each Compound

For the compound \( ext{H-COOH}\), identify it as a carboxylic acid series, represented by \( ext{R-COOH}\). For \( ext{CH}_3 ext{COCH}\), identify it as a ketone series, represented by \( ext{R'-CO-R''}\). For \( ext{H-CH=CH}_2\), identify it as an alkene series, represented by \( ext{R-CH=CH}_2\).

Determine the General Formula for Each Series

Carboxylic acids have the general formula \(C_nH_{2n+1}COOH\). Ketones have the formula \(C_nH_{2n}CO\). Alkenes with one double bond have the formula \(C_nH_{2n}\).

Draw Formulas for Carboxylic Acids

For \( ext{H-COOH}\), the first five members based on \(C_nH_{2n+1}COOH\) are: 1. \( ext{H-COOH}\) (formic acid) 2. \( ext{CH}_3 ext{COOH}\) (acetic acid) 3. \( ext{C}_2 ext{H}_5 ext{COOH}\) (propionic acid) 4. \( ext{C}_3 ext{H}_7 ext{COOH}\) (butyric acid) 5. \( ext{C}_4 ext{H}_9 ext{COOH}\) (valeric acid).

Draw Formulas for Ketones

For \( ext{CH}_3 ext{COCH}\), the first five members are: 1. \( ext{CH}_3 ext{COCH}_3\) (acetone) 2. \( ext{C}_2 ext{H}_5 ext{COCH}_3\) (butanone) 3. \( ext{C}_3 ext{H}_7 ext{COCH}_3\) (2-pentanone) 4. \( ext{C}_4 ext{H}_9 ext{COCH}_3\) (2-hexanone) 5. \( ext{C}_5 ext{H}_{11} ext{COCH}_3\) (2-heptanone).

Draw Formulas for Alkenes

For \( ext{H-CH=CH}_2\), the first five members are: 1. \( ext{H-CH=CH}_2\) (ethylene) 2. \( ext{CH}_3 ext{-CH=CH}_2\) (propylene) 3. \( ext{C}_2 ext{H}_5 ext{-CH=CH}_2\) (1-butene) 4. \( ext{C}_3 ext{H}_7 ext{-CH=CH}_2\) (1-pentene) 5. \( ext{C}_4 ext{H}_9 ext{-CH=CH}_2\) (1-hexene).

Key concepts

Carboxylic Acids

Carboxylic acids are a fundamental part of organic chemistry and belong to a homologous series characterized by the functional group \(-COOH\). This group is consistent across all carboxylic acids, giving them similar chemical properties. The general formula for carboxylic acids is \(C_nH_{2n+1}COOH\), where \(n\) begins at 0. Each member of this series differs from the next by a \(CH_2\) unit. This repetitive unit forms the basis for naming and understanding these compounds.

• Formic acid \(H-COOH\): The simplest carboxylic acid with no carbon chain.
• Acetic acid \(CH_3COOH\): Familiar as vinegar, with one carbon in its chain.
• Propionic acid \(C_2H_5COOH\): Found in milk and cheese.
• Butyric acid \(C_3H_7COOH\): Known for its rancid, buttery smell.
• Valeric acid \(C_4H_9COOH\): Used in manufacturing flavors.
  

These acids demonstrate the classic properties of carboxyl groups, such as the ability to donate a hydrogen ion, making them slightly acidic. They are widely used in industries ranging from food manufacturing to pharmaceuticals.

Ketones

Ketones are a group of organic compounds where a carbonyl group \(C=O\) is bonded to two carbon atoms. The typical structure for ketones is represented as \(R'-CO-R''\), indicating varied carbon chains around the carbonyl. The general formula for ketones is \(C_nH_{2n}CO\), symbolizing similar structure but different chain lengths. These compounds often serve as solvents and in the synthesis of plastics and perfumes.

• Acetone \(CH_3COCH_3\): A common solvent and the simplest ketone.
• Butanone \(C_2H_5COCH_3\): Known as methyl ethyl ketone (MEK), also used as a solvent.
• 2-Pentanone \(C_3H_7COCH_3\): Has applications in chemical manufacturing.
• 2-Hexanone \(C_4H_9COCH_3\): Often used in synthetic procedures.
• 2-Heptanone \(C_5H_{11}COCH_3\): Employed for flavor and fragrance production.
  

Ketones are known for their sweet-smelling aromas due to the carbonyl group. Their structures and properties allow them to be effective intermediates in various organic reactions.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon-carbon double bond \(C=C\). This double bond is what sets alkenes apart from alkanes and gives them unique characteristics. Alkenes have the general formula \(C_nH_{2n}\), which allows easy prediction of their molecular structure based on the number of carbon atoms. The simplest alkene is ethylene, which is used widely in the production of polyethylene, a common plastic.

• Ethylene \(H-CH=CH_2\): A building block for various polymers.
• Propylene \(CH_3-CH=CH_2\): Serves as a monomer for polypropylene fabrication.
• 1-Butene \(C_2H_5-CH=CH_2\): Utilized in the synthesis of polybutene and butadiene.
• 1-Pentene \(C_3H_7-CH=CH_2\): An important petrochemical used in chemical additives.
• 1-Hexene \(C_4H_9-CH=CH_2\): Applied in the manufacturing of polyethylene.
  

Alkenes’ double bonds make them reactive and useful in various chemical reactions, such as polymerization and halogenation. They offer a versatile starting point for synthesizing more complex molecules.