Problem 17 - General Chemistry: Principles and Modern Applications

Question

Identify the functional group in each compound (i.e., alcohol, amine, etc.). (a) \(\mathrm{CH}_{3} \mathrm{CHBrCH}_{2} \mathrm{CH}_{3}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CHO}\) (c) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{OH})_{2}\).

Step-by-Step Solution

Answer

(a) The functional group is an Alkyl Halide. (b) The functional group is an Aldehyde. (c) The functional group is a Ketone. (d) The functional group is a Phenol.

Step 1: Identify the Functional Group in (\mathrm{CH}_{3} \mathrm{CHBrCH}_{2} \mathrm{CH}_{3})

Identifying the functional group involves looking for the distinctive group of atoms. Here, the Bromine (Br) atom attached to the carbon chain indicates that this molecule is an Alkyl Halide.

Step 2: Identify the Functional Group in (\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CHO})

In this molecule, the distinctive functional group is the \(\mathrm{CHO}\) group at the end of the carbon chain, which is indicative of an Aldehyde.

Step 3: Identify the Functional Group in (\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3})

The \(\mathrm{CO}\) group in the middle of the carbon chains suggests that this molecule is a Ketone, since ketones have a carbonyl functional group (\(\mathrm{C=O}\)) within the carbon chain.

Step 4: Identify the Functional Group in (\mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{OH})_{2})

The presence of the two Hydroxyl (\(\mathrm{OH}\)) groups in the compound is a distinctive feature of a Phenol, a special kind of Alcohol where the hydroxyl group is directly attached to a benzene ring.

Key Concepts

Alkyl Halides

In organic chemistry, identifying functional groups is crucial for understanding a compound's properties and reactivity. An alkyl halide, also known as haloalkane, features a halogen atom bonded to an alkyl group. This halogen can be fluorine, chlorine, bromine, or iodine. In our specific example

• The compound is \( \mathrm{CH}_{3} \mathrm{CHBrCH}_{2} \mathrm{CH}_{3} \)
• Bromine (\( \mathrm{Br} \)) acts as the halogen atom.

The presence of bromine indicates that the compound belongs to the alkyl halides family. Understanding this group's chemistry helps in predicting reactions, like nucleophilic substitutions, which are common with alkyl halides.

Aldehydes

Aldehydes are characterized by the presence of the carbonyl group (\( \mathrm{C=O} \)) at the end of a carbon chain. This position distinguishes them from ketones, where the carbonyl group is positioned within the chain. In the molecule

• \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CHO} \),
• The functional group \( \mathrm{CHO} \) represents an aldehyde.

Aldehydes are versatile in organic synthesis, commonly oxidized to carboxylic acids or reduced to alcohols. The aromatic ring in our example adds more stability and affects the typical reactions aldehydes undergo.

Ketones

Ketones are another class of carbonyl-containing compounds but with the carbonyl group (\( \mathrm{C=O} \)) located between two carbon atoms. This internal position is what sets them apart from aldehydes. Our compound

• \( \mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3} \)
• has a central \( \mathrm{CO} \) group.

Due to their symmetrical structure, ketones do not easily oxidize, contrasting with aldehydes. This stability makes them useful in various industrial applications, like in the production of solvents.

Phenols

Phenols are a special kind of alcohol where the hydroxyl group (\( \mathrm{OH} \)) is directly attached to a benzene ring. This unique structure gives phenols distinctive properties compared to regular alcohols. For instance,

• The compound is \( \mathrm{C}_{6} \mathrm{H}_{4}(\mathrm{OH})_{2} \)
• It contains two hydroxyl groups, which suggests it's a dihydroxy derivative.

Phenols are more acidic than regular alcohols, due to the stabilization of the phenolate ion by the aromatic ring. This property makes them significant in disinfection and in the synthesis of various chemical compounds.