Question

The number of possible isomeric compounds that can be formed by substitution of two hydrogen atoms of propane by two chlorine atoms is (a) 2 (b) 3 (c) 4 (d) 5

Short answer

Answer: 4

Step-by-step solution

Propane Structure

First, let's recall the structure of propane. Propane is an alkane with three carbon atoms, so its formula is C3H8. The structure of propane can be represented as follows: CH3-CH2-CH3

Identify Possible Substitution Sites

Next, we need to determine the possible positions where two hydrogen atoms can be replaced by two chlorine atoms. In propane, there are two types of carbons: the end carbons (1 and 3) and the middle carbon (2). Each of these carbons has different numbers of hydrogen atoms attached to them. Carbon 1 and 3: CH3 Carbon 2: CH2

Replace Hydrogen Atoms with Chlorine Atoms

Now, we will create isomers by replacing two hydrogen atoms with two chlorine atoms at different carbon positions. 1. Two chlorine atoms at Carbon 1: ClCH2-CH2-CH3 - This isomer is called 1,1-dichloropropane 2. Two chlorine atoms at Carbon 2: CH3-CCl2-CH3 - This isomer is called 2,2-dichloropropane 3. One chlorine atom at Carbon 1 and one chlorine atom at Carbon 2: ClCH2-CHCl-CH3 - This isomer is called 1,2-dichloropropane 4. One chlorine atom at Carbon 1 and one chlorine atom at Carbon 3: ClCH2-CH2-CH2Cl - This isomer is called 1,3-dichloropropane After drawing all possible isomers, we can conclude that there are 4 different isomeric compounds that can be formed when two hydrogen atoms of propane are replaced by two chlorine atoms. Therefore, the correct answer is (c) 4.

Key concepts

Propane Structure

Understanding the structure of propane is foundational in organic chemistry. Propane, a member of the alkane family, is a simple hydrocarbon with the molecular formula \( C_3H_8 \). Imagine it as a chain of three carbon atoms, each bonded to sufficient hydrogen atoms to satisfy carbon's valency of four. The end carbons form three bonds with hydrogen, creating the \(CH_3\) groups, while the central carbon forms two bonds with hydrogen, producing a \(CH_2\) group. This gives us an overall structure of \(CH_3-CH_2-CH_3\).

This straightforward skeleton is essential for understanding how propane reacts, especially when it engages in a substitution reaction, which leads to the formation of various isomeric compounds.

Importance of Carbon Bonding

The nature of carbon to form four bonds makes it versatile and allows for numerous compounds with distinct properties. In propane's case, the way hydrogen atoms are arranged opens up the possibilities for isomer formation through their replacement with other atoms or groups.

Substitution Reaction

Substitution reactions are a crucial concept in organic chemistry where one atom or group of atoms is replaced by another atom or group. Focus on alkanes like propane: a substitution reaction often involves the replacement of hydrogen atoms with halogens.

Imagine a substitution reaction as a formal dance where dancers swap partners. In this molecular dance, a halogen 'taps out' a hydrogen atom and takes its place on the carbon skeleton. This process changes the molecule's structure and can create isomers, molecules with the same molecular formula but with different arrangements of atoms.

Consideration of Reactive Sites

In the case of propane, the end carbons have hydrogen atoms that are more accessible, making them more likely candidates for substitution. The central carbon, while also a potential substitution site, will lead to a different kind of isomer when its hydrogens are replaced.

Halogen Derivatives of Alkanes

Halogen derivatives of alkanes, such as chlorinated propane, are a group of compounds where one or more halogen atoms (like chlorine, fluorine, bromine, or iodine) have replaced hydrogen atoms in an alkane. The result is a vast array of compounds with diverse chemical and physical properties. Halogenation, the process of introducing a halogen atom into an organic compound, is a type of substitution reaction.

The variability in bonding sites for the halogens produces isomers, each with unique characteristics.

Exploration of Isomerism

Each possible arrangement of halogen atoms on the propane chain results in a different isomer. For instance, in dichloropropane isomers, their physical properties such as boiling points and densities can vary, which is significant in industrial applications. Understanding the principles of how these derivatives form and relate to each other not only helps in synthesis but also in the development of materials and pharmaceuticals.