Question

(a) What is a functional group? (b) What functional group characterizes an alcohol? (c) With reference to Exercise \(2.75\), write a structural formula for 1 -butanol, the alcohol derived from butane, by making a substitution on one of the end carbon atoms.

Short answer

(a) A functional group is a specific group of atoms within a molecule responsible for the characteristic chemical reactions of that molecule. It is the chemically reactive part of the molecule that undergoes transformations in chemical reactions. (b) The functional group characterizing an alcohol is the hydroxyl group (-OH), represented by the general formula R-OH, where R is an alkyl group. (c) The structural formula for 1-butanol, derived from butane (C₄H₁₀) with a substitution on one of the end carbon atoms by a hydroxyl group, is CH₃CH₂CH₂CH₂OH: H H H | | | H-C-C-C-C-H | OH

Step-by-step solution

(a) Define functional group

A functional group is a specific group of atoms within a molecule that is responsible for characteristic chemical reactions of that molecule. Functional groups are the chemically reactive part of the molecule that undergoes transformations in chemical reactions.

(b) Identify the alcohol functional group

The functional group that characterizes an alcohol is the hydroxyl group (-OH). An alcohol can be represented by the general formula R-OH, where R is an alkyl group.

(c) Draw the structural formula for 1-butanol

To draw the structural formula for 1-butanol, we need to start with the structure of butane, which has the formula C₄H₁₀. Butane has a linear structure with four carbon atoms in a row: H H H H | | | | C-C-C-C | | | | H H H H To derive 1-butanol from butane, we need to substitute one of the hydrogen atoms on an end carbon atom (in this case, the first carbon atom) with the hydroxyl group (-OH). The structural formula for 1-butanol is: H H H | | | H-C-C-C-C-H | OH Thus, the structural formula for 1-butanol is CH₃CH₂CH₂CH₂OH.

Key concepts

Understanding Alcohols

Alcohols are a class of organic compounds that play an important role in various biological and chemical processes. They are characterized by the presence of at least one hydroxyl group (-OH) attached to a saturated carbon atom. This means that the carbon atom, also known as the **alkyl group**, is saturated with hydrogen atoms and has single bonds with other atoms. The general formula for an alcohol is represented as R-OH, where R is the alkyl group.

Key features of alcohols include:

• **Polar Nature**: The hydroxyl group is polar, which often makes alcohols soluble in water due to hydrogen bonding.
• **Versatile Uses**: Alcohols are widely used in industry as solvents and as intermediates in the synthesis of other compounds.
• **Common Examples**: Ethanol, used in alcoholic beverages; isopropanol, used as a disinfectant.

Understanding the structure and properties of alcohols is fundamental for studying organic chemistry.

Exploring 1-Butanol

1-Butanol is a type of alcohol derived from butane. Butane is a hydrocarbon with four carbon atoms connected in a chain and is represented by the formula C₄H₁₀. To obtain 1-butanol from butane, a hydroxyl group is substituted for a hydrogen atom on the first carbon atom of the chain. This transformation is crucial because it changes the compound from an alkane to an alcohol.

The structural formula for 1-butanol is written as CH₃CH₂CH₂CH₂OH and visually depicted as:

• H H H
• | | |
• H-C-C-C-C-H
• |
• OH

This arrangement helps illustrate the linearity of the molecule with the hydroxyl group at one end, which is typical for primary alcohols like 1-butanol. 1-Butanol serves various functions, including use as a solvent and in the manufacture of plastics and rubber.

The Role of Hydroxyl Groups

The hydroxyl group (-OH) is the defining functional group for alcohols and is responsible for numerous chemical properties. Each hydroxyl group consists of an oxygen atom bonded to a hydrogen atom and linked to the carbon framework of the molecule.

The presence of the hydroxyl group provides several important characteristics:

• **Hydrogen Bonding**: Hydroxyl groups engage in hydrogen bonding, which contributes to higher boiling points compared to other molecules of similar molecular weight.
• **Reactivity**: The -OH group can participate in various chemical reactions, forming esters, ethers, and more.
• **Solubility**: Compounds with hydroxyl groups tend to be more soluble in water due to their ability to form hydrogen bonds.

The hydroxyl group's ability to interact with both polar and nonpolar substances makes alcohols versatile, influencing their behavior in chemical reactions and their utility in different applications.