Question

2, 3-dimethyl hexane contains .... tertiary.... secondary and \(\ldots \ldots\) primary carbon atoms, respectively. (a) \(2,4,3\) (b) \(3,2,4\) (c) \(4,3,2\) (d) \(2,2,4\)

Short answer

The correct answer is option (d) 2, 2, 4.

Step-by-step solution

Understanding the Structure

The name "2, 3-dimethyl hexane" provides the information needed to draw this molecule. It is a hexane chain with methyl groups attached at the 2nd and 3rd carbon atoms. Start by drawing a straight chain of six carbon atoms (hexane) and then add a methyl group (-CH₃) to the 2nd and 3rd carbon atoms of this chain.

Assigning Carbon Types

In organic chemistry, carbon atoms are classified based on how many other carbon atoms they are bonded to: primary (1 other carbon), secondary (2 other carbons), tertiary (3 other carbons), and quaternary (4 other carbons). Examine each carbon atom in the 2,3-dimethyl hexane structure to determine which category they fall into.

Identifying Primary Carbons

Primary carbons are bonded to only one other carbon. In 2,3-dimethyl hexane, these are the terminal carbons of the hexane chain (the 1st and 6th carbons), each attached only to the next carbon in the chain, as well as the ends of the methyl groups.

Identifying Secondary Carbons

Secondary carbons are bonded to two other carbons. In the hexane chain of 2,3-dimethyl hexane, the 4th and 5th carbons are secondary as they are each bonded to two other carbons in the chain.

Identifying Tertiary Carbons

Tertiary carbons are bonded to three other carbons. The 2nd and 3rd carbons of the hexane chain are each bonded to two carbons in the chain and the extra methyl group, making them tertiary carbons.

Counting Each Type of Carbon

Count the number of each type of carbon based on the identifications: - Primary: 4 (1st and 6th in the chain, plus ends of methyl groups) - Secondary: 1 (4th and 5th in the chain) - Tertiary: 2 (2nd and 3rd carbons) The correct configuration is primary: 4, secondary: 1, tertiary: 2.

Key concepts

Carbon Classification

Carbon classification in organic chemistry revolves around how many other carbon atoms a particular carbon atom is bonded to. Understanding these classifications is crucial because they help predict the reactivity and properties of carbon-containing compounds. Let's break down these classifications:

• Primary Carbon: This carbon atom is bonded to only one other carbon atom and is often located at the end of a chain. They are denoted often as having \(1^\circ\) classification.
• Secondary Carbon: A carbon atom bonded to two other carbons. These are typically found in the middle of a chain and are always \(2^\circ\) carbons.
• Tertiary Carbon: This carbon is attached to three other carbon atoms and has \(3^\circ\) classification. These carbons often have unique reactivity conditions compared to the first two types.
• Quaternary Carbon: Although not present in our original molecule, these are bonded to four other carbon atoms, making them \(4^\circ\) carbons.

In our exercise with 2,3-dimethyl hexane, identifying these different types of carbons helps us ensure we have fully understood their locations and roles in the molecule.

Hydrocarbons

Hydrocarbons are organic compounds composed entirely of hydrogen and carbon atoms. They form the foundational framework for most organic molecules and can be categorized based on their structures:

• Alkanes: Saturated hydrocarbons with single bonds between carbon atoms. They have the general formula \(C_nH_{2n+2}\) and are relatively non-reactive.
• Alkenes: Unsaturated hydrocarbons with at least one carbon-carbon double bond, having the formula \(C_nH_{2n}\).
• Alkynes: These possess one or more carbon-carbon triple bonds, following the formula \(C_nH_{2n-2}\).
• Aromatics: Hydrocarbons that contain one or more benzene rings. They have distinct chemical behavior due to their unique structure.

In the context of 2,3-dimethyl hexane, we are dealing with an alkane, as all the carbon-carbon connections are single bonds, aligning with the typical structure and properties of alkanes.

Naming Organic Compounds

The naming of organic compounds follows systematic rules to ensure every chemist interprets the molecule in the same way. This system is often referred to as the IUPAC (International Union of Pure and Applied Chemistry) nomenclature.

Here’s how we can name a molecule, such as 2,3-dimethyl hexane, in a systematic way:

• Identify the Longest Chain: Start by finding the longest continuous chain of carbon atoms in the molecule. In this case, it’s a six-carbon chain, earning the root name 'hexane'.
• Number the Chain: Number the chain in such a way that the substituents get the lowest possible numbers. Here, methyl groups are on the 2nd and 3rd carbon atoms.
• Identify and Name Substituents: Methyl groups are the substituents, and they are identified before the root name. The prefix 'di-' indicates that there are two identical substituents.
• Combine and Arrange: Combine the names and numbers into a single compound name: 2,3-dimethylhexane.

With these guidelines, organic compounds are named in a way that reveals their structure and is universally understood.