On substitution of one H by a Cl in the isomers of C5 H12,(a) which isomer gives only a primary

step 1 Question is that two isomeric alkenes A and B having molecular formula on adding hydrogen gives

On substitution of one H by a Cl in the isomers of C5...

On substitution of one $\mathrm{H}$ by a $\mathrm{Cl}$ in the isomers of $\mathrm{C}_5 \mathrm{H}_{12},(a)$ which isomer gives only a primary halide? (b) Which isomers give secondary halides? (c) Which isomer gives a tertiary halide? (a) 2,2-Dimethylpropane. (b) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_3$ gives 2-chloropentane and 3-chloropentane. 2-Methylbutane gives 2-chloro-3-methylbutane. (c) 2-Methylbutane gives 2-chloro-2-methylbutane.

On substitution of one $\mathrm{H}$ by a $\mathrm{Cl}$ in the isomers of $\mathrm{C}_5 \mathrm{H}_{12},(a)$ which isomer gives only a primary halide? (b) Which isomers give secondary halides? (c) Which isomer gives a tertiary halide?
(a) 2,2-Dimethylpropane. (b) $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CH}_3$ gives 2-chloropentane and 3-chloropentane. 2-Methylbutane gives 2-chloro-3-methylbutane. (c) 2-Methylbutane gives 2-chloro-2-methylbutane.

Key Concepts

Structural Isomerism

Structural isomerism refers to compounds that share the same molecular formula but differ in the connectivity of their atoms. In organic chemistry, this concept explains the existence of different alkane isomers, such as those with varying chain branching, which leads to differences in physical and chemical properties and determines how they react under substitution conditions.

Carbon Classification by Degree of Substitution

Carbon atoms in organic molecules are classified as primary, secondary, or tertiary based on the number of carbon atoms directly attached to them. This classification is crucial because it affects the reactivity and stability of intermediates during chemical reactions, particularly in substitution reactions, where the nature of the carbon (primary, secondary, or tertiary) determines the type of halide product formed.

Regioselectivity in Substitution Reactions

Regioselectivity refers to the preference of a chemical reaction to take place at one direction or position over others in a molecule. In the context of alkane halogenation, the different environments of hydrogen atoms (attached to primary, secondary, or tertiary carbons) lead to preferential formation of certain isomers. This concept helps in predicting which positions in the molecular structure will be more likely substituted to give primary, secondary, or tertiary halides.

Free Radical Halogenation Mechanism

The free radical halogenation mechanism involves the substitution of a hydrogen atom by a halogen atom in alkanes through a chain reaction process that includes initiation, propagation, and termination steps. The reaction’s outcome is influenced by the stability of the radical intermediates formed at different carbon centers, with tertiary radicals being more stable than secondary, and secondary more stable than primary, which in turn affects the selectivity of halide formation.

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