Question

The number of possible open chain (acyclic) isomeric compounds for molecular formula \(\mathrm{C}_{5} \mathrm{H}_{10}\) would be (a) 5 (b) 6 (c) 7 (d) 4

Short answer

The number of open-chain isomers for \(\mathrm{C}_5\mathrm{H}_{10}\) is 5.

Step-by-step solution

Understand the Problem

We need to determine how many different isomeric open-chain (acyclic) compounds can be formed with the molecular formula \(\mathrm{C}_5\mathrm{H}_{10}\). The formula indicates that the compounds are alkenes, as the general formula for alkenes is \(\mathrm{C}_n\mathrm{H}_{2n}\).

Identify Basic Alkene Structure

For open-chain alkenes (acyclic), we start with the simplest alkene having 5 carbon atoms. The basic structure starts with a double bond between any two carbons, which affects how we count isomers.

Arrange Double Bond

For a 5-carbon alkene, the double bond can be placed between different sets of carbon atoms: between C1 and C2, C2 and C3, and C3 and C4, leading potentially to different isomers. Placing the bond between C4 and C5 would be the same as C1 and C2 due to symmetry, and similar logic applies for others, so we focus on 3 main possibilities.

Consider Chain Branching

We can also create branched isomers. By placing branches like methyl groups, we can form additional unique isomers. The key possible branches are: - 2-methyl-1-butene - 3-methyl-1-butene - 2-methyl-2-butene Each represents a distinct compound.

Count Isomers

List the valid structures: 1. Pent-1-ene 2. Pent-2-ene 3. 2-Methylbut-1-ene 4. 3-Methylbut-1-ene 5. 2-Methylbut-2-ene As shown, there are 5 distinct structures.

Key concepts

Alkanes

Alkanes are a significant group of hydrocarbons that contain only carbon and hydrogen atoms, held together by single bonds. These single bonds are known as sigma bonds and they allow the carbon atoms in alkanes to form long chains or branched structures. This makes alkanes saturate hydrocarbons, meaning they have the highest number of hydrogen atoms possible bonded to the carbon chain. The general formula for alkanes is \(\mathrm{C}_n\mathrm{H}_{2n+2}\), where \( n \) is the number of carbon atoms.
Alkanes are generally unreactive, but they can combust in the presence of oxygen to form carbon dioxide and water. This lack of reactivity makes alkanes useful as fuels. While alkanes are generally not involved in forming isomers with a molecular formula of \(\mathrm{C}_{5}\mathrm{H}_{10}\), understanding the basic structure of alkanes is crucial in organic chemistry.

Alkenes

Alkenes are hydrocarbons similar to alkanes, but with at least one carbon-carbon double bond. This double bond is key to their reactivity and affects their structural possibilities, allowing them to form isomers. The general formula for open-chain (acyclic) alkenes is \( \mathrm{C}_n\mathrm{H}_{2n} \).
Due to the presence of the double bond, alkenes exhibit what is known as "cis-trans" isomerism or "geometric" isomerism. In alkenes with more than three carbon atoms, the location of the double bond, as well as chain branching, contributes to the possible number of isomeric structures.
For a molecule like \( \mathrm{C}_5\mathrm{H}_{10} \), which is an alkene, potential isomers include variations in the placement of the double bonds and the addition of methyl groups, leading to branched structures such as 2-methylbut-1-ene and 3-methylbut-1-ene.

Molecular Structure

Molecular structure in chemistry refers to the three-dimensional arrangement of atoms in a molecule. It encompasses how atoms are connected, the angles between bonds, and the spatial orientation of these bonds.
Understanding molecular structure is crucial for predicting the properties and reactivity of the compound. Variations in bond angles and geometry can lead to entirely different isomers that may have distinct chemical and physical properties. In hydrocarbons, particularly alkenes, slight changes in the structure, such as the position of a double bond or the presence of branches, result in different isomers.
For the molecular formula \( \mathrm{C}_5\mathrm{H}_{10} \), understanding the molecular structure is key to identifying the different isomers. These include ensuring that the double bond is properly placed and considering all possible branch points, influencing the compound's identity and properties.

Organic Chemistry

Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds. These compounds are the building blocks of life and comprise a myriad of substances, from a simple alkane to complex biomolecules.
In organic chemistry, understanding the concept of isomerism is fundamental. Isomers are molecules with the same molecular formula but different arrangements of atoms in space. Isomerism is especially prevalent in organic compounds due to carbon's versatility in forming chains and rings.
The study of alkenes and their isomers, such as those described by the molecular formula \( \mathrm{C}_5\mathrm{H}_{10} \), is a typical topic in organic chemistry. This involves examining how molecules can have the same atoms but differ in the geometry of the double bond or the branching of the carbon chain. Comprehending these variations deepens one's understanding of how molecular structure influences chemical behavior and reactivity in organic compounds.