Problem 16 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The IUPAC name of the compound \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2}\) is (a) 1,1 -dimethyl \(-2\)-propene (b) 3-methyl-1-butene (c) 2-vinylpropane (d) 1-isopropylethylene

Step-by-Step Solution

Answer

The IUPAC name is (b) 3-methyl-1-butene.

Step 1: Determine the Longest Carbon Chain

The first step in IUPAC naming is to identify the longest carbon chain in the compound. In this structure, we have a total of four carbon atoms in the longest chain: two from the double bond (from CH2=CH) and two from the side chain (from the CH(CH3)2). This makes it a butane derivative because the longest chain consists of four carbon atoms.

Step 2: Identify the Functional Group and Its Position

The compound contains a carbon-carbon double bond, which takes priority in naming. The double bond affects the suffix of the base name, and its position must be identified. Here, the double bond starts at carbon 1 when numbering from the end closest to the double bond, thus contributing to the name 'butene' with a 1-position for the double bond: '1-butene'.

Step 3: Identify Substituents

We have a methyl group (CH3) as a side chain on the second carbon of the main chain. Count the carbon atoms starting from the end closest to the double bond. The substituent is on the third carbon of the main chain (when counting from the end opposite the double bond), thus making it a 3-methyl substituent.

Step 4: Combine the Components for the IUPAC Name

Combine the components of the name: the prefix for the substituent (3-methyl), the main chain name (butene), and the position of the double bond if needed (1-butene). By combining, we get '3-methyl-1-butene' as the full IUPAC name of the compound.

Key Concepts

Organic Chemistry

Organic chemistry focuses on the study of carbon-containing compounds, like the hydrocarbons and derivatives you encounter every day. This fascinating branch of chemistry is crucial for understanding many natural and synthetic materials ranging from fuels to pharmaceuticals.
The backbone of organic compounds is made up of carbon atoms linked together, while hydrogen, oxygen, nitrogen, and other elements usually form additional bonds, completing these molecular structures.
In the world of organic chemistry, naming compounds in a standardized way is essential for effective communication. The IUPAC nomenclature system helps label a vast array of organic molecules so that chemists worldwide can easily understand each other.
Understanding this system is foundational to exploring and mastering organic chemistry.

Alkenes

Alkenes are a group of hydrocarbons that contain at least one double bond between carbon atoms, represented by the formula \\( ext{C}_{n} ext{H}_{2n} \\).
This distinguishing double bond is essential, as it influences the chemical reactivity and properties of these compounds, allowing them to participate in a variety of chemical reactions.
In IUPAC nomenclature, alkenes are often named with the suffix '-ene' to signify the presence of a carbon-carbon double bond.

Examples include Ethene (C2H4) and Propene (C3H6).

The position of the double bond is specified with a number placed in front of the base name, so it’s clear which carbon it starts from. This helps avoid any confusion, especially when isomers (compounds with the same formula but differently arranged atoms) are involved.

Structural Isomers

Structural isomers are fascinating because they share the same molecular formula but have different arrangements of atoms. It makes them unique in terms of their physical and chemical properties.
Imagine the difference between butane, a straight chain of four carbon atoms, and isobutane, a branched form of butane - both have the formula \\( ext{C}_{4} ext{H}_{10} \\).
These variations lead to different boiling points, melting points, and reactivities, among other properties.

Understanding and recognizing structural isomers is critical for correctly determining the IUPAC name of a compound. This skill ensures accurate and meaningful communication in organic chemistry.

When naming alkenes, it’s even more important to note structural isomers, as the position of the double bond can significantly alter the compound’s structure and properties.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules.
Each functional group behaves consistently in different compounds. Knowing them is essential for predicting the reactivity and interaction of molecules.
In the realm of alkenes, the carbon-carbon double bond acts as the key functional group. It not only dictates the compound's reactivity but also influences its overall geometry and chemical behavior.

Other common functional groups include alcohols (-OH), carboxylic acids (-COOH), and amines (-NH2).

When naming alkenes, the double bond takes precedence because of its significant impact on the molecule’s properties. Understanding functional groups and their hierarchy is crucial for anyone studying organic chemistry.