Question

In the alkane \(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{2}-\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}-\mathrm{CH}_{2}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\), identify \(1^{\circ}, 2^{\circ}, 3^{\circ}\) carbon atoms and give the number of \(\mathrm{H}\) atoms bonded to each one of these.

Short answer

1° has 3 hydrogens, 2° has 2 hydrogens, 3° has 1 hydrogen per carbon.

Step-by-step solution

Understand Alkane Structure

The given alkane is \( \mathrm{C}_8\) based on the molecular formula. It has linear and branched chains, which we need to analyze to identify the degree of each carbon atom.

Identify Primary (1°) Carbon Atoms

A primary carbon (\(1^{\circ}\)) is a carbon atom bonded to only one other carbon atom. In the given compound, the primary carbons are found at the ends or in the branches connecting to a single carbon atom. Count the primary carbon atoms, which are the first and last carbon atom, as well as the ends of each branch.

Calculate Hydrogen Atoms on 1° Carbons

Each \(1^{\circ}\) carbon is bonded to three hydrogen atoms. Count the number of such carbons and multiply by 3 to get the total hydrogen atoms bonded to \(1^{\circ}\) carbons.

Identify Secondary (2°) Carbon Atoms

A secondary carbon (\(2^{\circ}\)) is bonded to two other carbon atoms. Identify these in the main chain where a carbon atom connects only to two other carbon atoms directly.

Calculate Hydrogen Atoms on 2° Carbons

Typically, each \(2^{\circ}\) carbon is bonded to two hydrogen atoms. Count the number of such carbons and multiply by 2 to find the total hydrogen atoms on \(2^{\circ}\) carbons.

Identify Tertiary (3°) Carbon Atoms

A tertiary carbon (\(3^{\circ}\)) is bonded to three other carbon atoms. These are found at branching points where three other carbon atoms meet. Identify these carbons in the alkane structure.

Calculate Hydrogen Atoms on 3° Carbons

Each \(3^{\circ}\) carbon is bonded to one hydrogen atom. Count the \(3^{\circ}\) carbons and calculate the total hydrogen atoms by considering one hydrogen per tertiary carbon.

Summarize Results

Combine the findings: the number of \(1^{\circ}\), \(2^{\circ}\), and \(3^{\circ}\) carbon atoms and their respective hydrogen counts: 1° carbons with 3 hydrogens, 2° carbons with 2 hydrogens, and 3° carbons with 1 hydrogen.

Key concepts

Primary Carbon Atoms

Primary carbon atoms, denoted as \(1^{\circ}\) carbons, are fundamental components within alkanes. These atoms are characterized by their connection to only one other carbon atom. As such, they are typically located at the terminal ends of the alkane molecule or at the end of a branch when the structure is branched.

In alkanes, primary carbons are vital for determining the molecule's reactivity and properties. For example, in the alkane \( \text{H}_3\text{C}-\text{CH}_2-\text{C}\left(\text{CH}_3\right)_2-\text{CH}_2-\text{CH}\left(\text{CH}_3\right)_2 \), primary carbon atoms can be identified at both ends of the molecule and the ends of any branches.

Each primary carbon typically connects to three hydrogen atoms. Thus, by identifying the number of primary carbon atoms in a given alkane, we can determine the total number of associated hydrogen atoms. This is crucial for calculating the molecular formula and understanding the molecular geometry. Analyzing the presence of primary carbons helps in deducing physical and chemical properties of the molecule.

Secondary Carbon Atoms

Secondary carbon atoms, labeled as \(2^{\circ}\) carbons, play a significant role in the structure of alkanes. These carbons are bonded to exactly two other carbon atoms.

Secondary carbons can be found along the main chain of an alkane or at the junctions within branched alkanes. Their presence in a molecule dictates the overall backbone structure. For instance, in the discussed alkane \( \text{H}_3\text{C}-\text{CH}_2-\text{C}\left(\text{CH}_3\right)_2-\text{CH}_2-\text{CH}\left(\text{CH}_3\right)_2 \), these secondary carbons are located where a transition from one carbon chain to another occurs without branching further.

Typically, each secondary carbon is bound to two hydrogen atoms. By counting the secondary carbons, the total hydrogen count associated with these atoms can be deduced. Understanding the placement of secondary carbons is essential for mapping out the molecule's structure and predicting its reaction behavior.

Tertiary Carbon Atoms

In alkanes, tertiary carbon atoms, represented as \(3^{\circ}\) carbons, are another important component. These are carbon atoms connected to three other carbon atoms.

Tertiary carbons are primarily found at branching points within an alkane chain. These atoms serve as critical junctures in the molecular structure, influencing the shape and flexibility of the alkane. In the illustrated alkane \( \text{H}_3\text{C}-\text{CH}_2-\text{C}\left(\text{CH}_3\right)_2-\text{CH}_2-\text{CH}\left(\text{CH}_3\right)_2 \), tertiary carbons are situated at the branching points where three other carbons meet.

Each tertiary carbon is connected to a single hydrogen atom. Recognizing tertiary carbons helps in predicting the alkane's reactivity patterns, as these carbons often present steric hindrance due to their surrounding carbon atoms. This feature makes them interesting in chemical reactions and syntheses of complex molecules.