NEET Chemistry: Alkenes geometrical isomerism and addition reactions Practice Questions

Correct answer: C — 2-Butene

Geometrical isomerism occurs in alkenes where each carbon of the double bond is attached to two different groups. 2-Butene (CH₃CH=CHCH₃) has two different groups on each carbon (methyl and ethyl groups), allowing for cis/trans isomerism. Propene and Propane do not have this structural arrangement to exhibit geometrical isomerism.

Correct answer: B — Presence of a C=C bond

Geometrical isomerism (cis-trans isomerism) requires restricted rotation around the double bond, which is characteristic of the C=C bond. The presence of two different groups on each carbon of the double bond is also required, but the C=C bond itself is the foundation of the isomerism possibility.

Correct answer: D — Optical and geometrical isomerism

If R is an unsymmetrical group, the alkene can exhibit both geometrical isomerism (if R is not H) and optical isomerism (if the molecule lacks a plane of symmetry).

Correct answer: B — trans-2-methylbut-2-ene

2-methylbut-2-ene is an asymmetrical alkene that can exist as cis or trans isomers, demonstrating geometrical isomerism.

Correct answer: D — 2-Bromopropane

Markovnikov's rule states that the hydrogen atom adds to the carbon with more hydrogen atoms. In the addition of HBr to propene, the bromine adds to the more substituted carbon, yielding 2-Bromopropane.

Correct answer: D — Hydrogenation

The reaction where hydrogen (H₂) is added across a multiple bond (alkene) to form a single bond (alkane) is specifically called hydrogenation.

Correct answer: A — Markovnikov's rule

The addition of HX (like HBr) to unsymmetrical alkenes follows Markovnikov's rule, where the hydrogen atom adds to the carbon with more hydrogen atoms, resulting in the formation of the more stable carbocation intermediate.

Correct answer: D — Geometrical isomerism

The arrangement of substituents on a double bond, leading to different spatial orientations (cis or trans), is defined as geometrical isomerism. Cis specifically refers to the configuration where the higher priority groups are on the same side of the double bond.

Correct answer: B — Alcohols

Alkenes react with water in the presence of a catalyst (acid) via acid-catalyzed hydration, which leads to the formation of alcohols. This reaction is known as hydration.

Correct answer: A — But-2-ene

Geometric isomerism (cis-trans isomerism) occurs in alkenes where restricted rotation is possible around the π-bond, which happens when both carbon atoms of the double bond are attached to two different groups. But-2-ene (CH₃CH=CHCH₃) has two different groups attached to each carbon, allowing for cis and trans isomers. Propene (CH₃CH=CH₂) does not have geometric isomers.

Correct answer: C — presence of a double bond

Geometrical isomerism (cis-trans isomerism) occurs when restricted rotation around a carbon-carbon double bond is possible, and the groups attached to each carbon are different, allowing for different spatial arrangements.

Correct answer: A — Isomerism due to restricted rotation about the π-bond

Geometric isomerism (cis-trans isomerism) in alkenes arises because rotation about the π-bond is restricted, leading to distinct spatial arrangements of substituents on the double bond.

Correct answer: D — 2-Butene

2-Butene (CH₃CH=CHCH₃) has restricted rotation, allowing for cis and trans geometric isomers. Propene (CH₃CH=CH₂) does not exhibit this isomerism.

Correct answer: C — cis-2-butene and trans-2-butene

2-butene (CH₃CH=CHCH₃) has two different geometric isomers: cis-2-butene (where the higher priority groups are on the same side) and trans-2-butene (where they are on opposite sides).

Correct answer: A — Markovnikov's rule

Markovnikov's rule states that in the addition of H-X across a double bond, the hydrogen atom adds to the carbon atom that already has more hydrogen atoms.