Problem 69 - General Chemistry

Question

Identify each of the following compounds. a. A gas with a sweetish odor that promotes the ripening of green fruit. b. An unsaturated compound of the formula \(\mathrm{C}_{7} \mathrm{H}_{8}\) that gives a negative test with bromine in carbon tetrachloride. c. A compound with an ammonia-like odor that acts as a base; its molecular formula is \(\mathrm{CH}_{5} \mathrm{~N}\). d. An alcohol used as a starting material for the manufacture of formaldehyde.

Step-by-Step Solution

Answer

a. Ethylene, b. Toluene, c. Methylamine, d. Methanol.

Step 1: Identify the Gas with a Sweetish Odor

The gas with a sweetish odor that promotes the ripening of green fruit is known as ethylene. Ethylene is a simple alkene with the formula \( \text{C}_2\text{H}_4 \) and is widely recognized for its role as a plant hormone that accelerates the ripening process.

Step 2: Identify the Unsaturated Compound

The compound with a formula \( \text{C}_7\text{H}_8 \) that gives a negative test with bromine in carbon tetrachloride is toluene. Toluene is an aromatic compound (a methyl group attached to a benzene ring) and does not react with bromine in the absence of light, which is why it gives a negative test with bromine.

Step 3: Identify the Compound with Ammonia-like Odor

The compound \( \text{CH}_5\text{N} \) with an ammonia-like odor that acts as a base is methylamine. Methylamine is a simple aliphatic amine that is known for its strong, ammonia-like smell and basic properties.

Step 4: Identify the Alcohol for Formaldehyde Production

The alcohol that is used as a starting material for the manufacture of formaldehyde is methanol. Methanol is a simple alcohol that, when oxidized, forms formaldehyde, which is utilized in numerous industrial processes.

Key Concepts

Alkenes

Alkenes are a fascinating class of organic compounds that are defined by the presence of at least one carbon-carbon double bond. This double bond makes alkenes unsaturated hydrocarbons, which means they have fewer hydrogen atoms than the maximum possible for the number of carbons. Ethylene, with the formula \(\text{C}_2\text{H}_4\), is a simple alkene. It is a gas with a sweetish smell and is particularly famous for its natural role in promoting the ripening of fruits. This property is due to its function as a plant hormone.

Alkenes are generally more reactive than their alkane counterparts due to the presence of the double bond. This bond can participate in a variety of addition reactions.

• Addition of halogens (like bromine) to form dihaloalkanes.
• Hydration to form alcohols.
• Hydrogenation to form alkanes.

These reactions make alkenes incredibly useful in chemical manufacturing and synthesis.

Aromatic Compounds

Aromatic compounds are a unique group of organic molecules known for their stable ring structures and pleasant odors. One classic example is toluene, which is a methyl group attached to a benzene ring. It has the molecular formula \( \text{C}_7\text{H}_8 \), illustrating its aromatic nature. Toluene's aromaticity is evidenced by its lack of reaction with bromine in carbon tetrachloride. This stability is a hallmark of aromatic compounds.

Aromatic compounds generally have several key properties:

• High stability due to delocalized electrons within the ring.
• Commonly undergo substitution reactions rather than additions.
• Have characteristic absorption of ultraviolet light.

Beyond toluene, aromatic compounds are used extensively in industry, often in the manufacture of dyes, pharmaceuticals, and even explosives, thanks to their diverse chemical behavior.

Amines

Amines are organic compounds that contain a nitrogen atom bonded to one or more alkyl groups. These compounds are derivatives of ammonia, \(\text{NH}_3\), and they retain a similar structure. Methylamine, \(\text{CH}_5\text{N}\), is a simple amine noted for its sharp, ammonia-like smell. It's an example of a primary amine, where one hydrogen atom in ammonia is replaced by a methyl group.

Amines are classified according to their structure:

• Primary amines have one substituent attached to the nitrogen.
• Secondary amines have two substituents.
• Tertiary amines have three substituents.

Amines act as bases, capable of accepting protons due to their lone pair of electrons on nitrogen. Their basic nature contributes to their role in pharmaceuticals, where they often aid in drug action through their interactions with biological systems.

Alcohols

Alcohols are organic compounds featuring a hydroxyl group (\(-\text{OH}\)) attached to a saturated carbon atom. Methanol, \(\text{CH}_3\text{OH}\), is a prototypical alcohol, widely used in the industry for its capacity to be converted into formaldehyde. This conversion is crucial in the production of a variety of materials, including plastics and resins.

The properties of alcohols include:

• Being polar, thus forming hydrogen bonds, which affects their boiling and melting points.
• Varied reactivity, including oxidation to form aldehydes, ketones, and acids.
• The capability to undergo substitution and elimination reactions.

In summary, alcohols such as methanol are foundational in both industrial applications and scientific research, proving indispensable across numerous fields.