Problem 16 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{C} \equiv \mathrm{N}\) and \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N} \sqsupseteq \mathrm{C}\) are which type of isomers? (a) tautomerism (b) position (c) functional (d) linkage

Step-by-Step Solution

Answer

The compounds are functional isomers.

Step 1: Identify the compounds

The compounds given in the question are \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{C} \equiv \mathrm{N} \) and \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N} \sqsupseteq \mathrm{C} \). The first formula denotes a nitrile group (\( -C \equiv N \)), where carbon is triple-bonded to nitrogen. The second formula denotes an isocyanide group (\( -N \equiv C \)), where nitrogen is triple-bonded to carbon.

Step 2: Understand functional groups involved

In these compounds, we have two functional groups: the nitrile group, where the carbon is attached to a nitrogen atom via a triple bond, and the isocyanide group, where the nitrogen atom is attached to a carbon atom via a triple bond. These involve the same atoms (C and N) arranged differently.

Step 3: Determine isomer type

Since both compounds involve the same atoms arranged differently in forms of their functional groups, they correspond to different functional groups (nitrile and isocyanide). This means these are functional isomers, as they fall into the category of having the same molecular formula but different types of functional groups.

Key Concepts

Nitrile Group

The nitrile group is a functional group commonly represented as \(-C \equiv N\). This means that a carbon atom is triple-bonded to a nitrogen atom. The triple bond is a characteristic feature, contributing to the physical and chemical properties of the compounds containing this group. These compounds are typically known as nitriles.

Nitriles often appear in a variety of organic compounds and are known for their distinct properties:

• Polar nature: The electronegativity difference between carbon and nitrogen creates a polar bond.
• Solubility: Nitriles are generally soluble in polar solvents due to their polarity.
• Reactivity: The triple bond can undergo various types of chemical reactions, allowing for diverse applications in organic synthesis.

Nitriles are versatile in organic chemistry, often used as intermediates in the synthesis of other compounds. They can be hydrolyzed to form carboxylic acids, thus playing a significant role in organic transformations.

Isocyanide Group

The isocyanide group, also known as the isonitrile group, is represented as \(-N \equiv C\). This involves a nitrogen atom triple-bonded to a carbon atom, the opposite of the nitrile group. Despite being similar in appearance, isocyanides and nitriles have different properties and reactivities.

Key characteristics of isocyanides include:

• Distinctive smell: Isocyanides are notorious for their pungent odor, which is quite different from the related nitriles.
• Chemical reactivity: Isocyanides can participate in unique reactions, such as the Passerini and Ugi multicomponent reactions, which are valuable in drug synthesis.
• Structural variance: Unlike nitriles, the electronic environment of isocyanides allows for different reactivity patterns despite the similar initial functional group representation.

Isocyanides are less common than nitriles but provide unique pathways in synthetic organic chemistry, particularly in the construction of complex molecules.

Triple Bond

A triple bond is a type of covalent bond where three pairs of electrons are shared between two atoms. In organic chemistry, triple bonds occur prominently in alkynes and nitriles, significantly influencing the molecular geometry and reactivity.

Here are important features of triple bonds:

• Linear geometry: The linear arrangement around the triple bond contributes to distinct spatial and electronic properties.
• High strength: Triple bonds are stronger than single or double bonds due to the multiple shared electron pairs, requiring more energy to break.
• Short bond length: Triple bonds are shorter than single and double bonds, reflecting their strong and multi-electron sharing nature.

Triple bonds enable various reactions in organic synthesis, such as addition reactions, which contribute to building more complex molecular architectures. Their presence is critical in defining the chemical properties and reactivity profiles of compounds containing them.