Problem 112 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following compound yields only one product on monobromination? (a) neopentane (b) aniline (c) phenol (d) toluene

Step-by-Step Solution

Answer

Neopentane yields only one product on monobromination.

Step 1: Understanding Monobromination

Monobromination is a substitution reaction where one hydrogen atom in an organic compound is replaced by a bromine atom. The number of products formed depends on the symmetry and structure of the compound undergoing bromination.

Step 2: Option Analysis: Neopentane

Neopentane has a highly symmetrical structure with all hydrogen atoms having the same environment. Upon monobromination, only one distinct product is formed as the bromine has no preference for any particular hydrogen atom.

Step 3: Option Analysis: Aniline

Aniline, with an 9-1H2 group, undergoes bromination primarily at the para position due to the activating effect of the amino group. However, bromination can also occur at the ortho position, leading to multiple products.

Step 4: Option Analysis: Phenol

Phenol has an 9-1H group that directs bromination primarily to ortho and para positions due to electron donation, thus yielding multiple products on monobromination.

Step 5: Option Analysis: Toluene

Toluene undergoes bromination mainly at the ortho and para positions relative to the methyl group because it activates these positions. This results in more than one monobromination product.

Step 6: Conclusion

Based on the analysis, neopentane is the only option that results in a single product on monobromination due to its complete symmetry.

Key Concepts

Substitution Reaction

Substitution reactions are a fundamental concept in organic chemistry, where one atom or group of atoms in a molecule is replaced by another atom or group. In the case of monobromination, a hydrogen atom in an organic compound is replaced by a bromine atom. This is specifically useful in transforming hydrocarbons into more reactive derivatives. These reactions often involve the use of halogen radicals, usually formed in the presence of light or heat. During a monobromination, the molecular structure of the hydrocarbon plays a key role in determining which hydrogen atom will be replaced. Symmetry and electron availability can affect which hydrogen is substituted. Understanding substitution reactions helps in predicting the products and controlling chemical reactions effectively.

Symmetry in Organic Compounds

Symmetry in organic compounds is a significant factor when analyzing possible reactions and their products, especially in reactions like monobromination. A symmetric molecule means that all similar atoms have an identical chemical environment. This property can simplify reactions because it will influence the number of distinct products formed. For example, when a molecule is perfectly symmetric, like neopentane, monobromination results in only one unique product. This is because any hydrogen atom can be replaced by a bromine atom without changing the molecular identity of the remaining structure. Utilizing symmetry helps to predict reaction pathways and simplifies computational chemistry models.

Neopentane

Neopentane is a compound known for its high symmetry. Its chemical structure is denoted as \((CH_3)_4C\). All twelve hydrogen atoms are equivalent due to the tetrahedral symmetry around the central carbon atom. This results in any monobromination targeting a hydrogen atom, producing only one unique product. Neopentane serves as an excellent example of how symmetry influences chemical reactions. This feature makes it unique among many hydrocarbons, which typically can yield multiple products upon reaction. Understanding the structure of neopentane illustrates why its reactions are more predictable and controlled.

Compound Structure Analysis

Compound structure analysis involves examining the molecular arrangement and the spatial configuration of its atoms. For organic chemists, understanding the geometry and symmetry of a compound is crucial to predicting its reactivity and interactions with other molecules. In the context of monobromination, analyzing the compound structure helps to determine where a bromine atom is likely to be substituted. For example, in neopentane, the structure's symmetry ensures that regardless of which hydrogen atom is replaced, the same compound configuration results, thus only a single product is formed. Structure analysis allows chemists to comprehend complex reactions and accurately foresee their outcomes, contributing to more effective synthesis strategies.