Chemistry Question Bank for Class 12 on “Haloalkanes & Haloarenes – Chemical Reactions – 2”.
1. As the stability of carbocation formed in the first step of SN1 reaction increases, the rate of the reaction _________
a) increases
b) decreases
c) remains same
d) may increase or decrease
Answer: a
Clarification: Greater the stability of the carbocation, greater will be the ease of formation from alkyl halide and faster will be the reaction rate.
2. The SN1 reaction cannot be carried out in which of the following media?
a) Acetic acid
b) Acetone
c) Ethanol
d) Water
Answer: b
Clarification: SN1 reactions are carried out in polar protic solvents like water, alcohol and acetic acid. These solvents promote the ionisation step by stabilising the ions by solvation.
3. If a compound does not affect the plane of plane polarised light when passed through it, the compound is said to be _________
a) optically active
b) optically inactive
c) dextrorotatory
d) laevorotatory
Answer: b
Clarification: When the plane of plane polarised light is rotated either to the left or right when passed through a compound, it is said to be optically active. Else, it is optically inactive.
4. Which of the following compounds does not have a stereocenter?
a) Propan-2-ol
b) Butan-2-ol
c) 2-Bromo-1-chlorobutane
d) 2-Bromopentane
Answer: a
Clarification: A stereocenter is an asymmetric carbon that has four different groups attached to it. Propan-2-ol has two methyl groups attached to the carbon.
5. Which of the following has a chiral carbon atom?
a) 2-Chloro-2-methylpentane
b) 1,1-Dibromoethane
c) Pentan-3-ol
d) 2-Bromopentane
Answer: d
Clarification: A chiral carbon atom is that which has four different substituent groups attached to it. 2-Bromopentane has one of each H, CH3, C3H7 and Br groups attached to its C atom.
6. What is the chirality of 2-Chlorobutane?
a) Chiral
b) Achiral
c) Superimposable mirror images
d) Symmetric
Answer: a
Clarification: 2-Chlorobutane has four different groups attached to the tetrahedral carbon and is chiral as it forms non-superimposable mirror images.
7. Predict the chirality of the shown compounds.
a) Both A and B are chiral
b) Both A and B are achiral
c) A is chiral and B is achiral
d) A is achiral and B is chiral
Answer: c
Clarification: The C atom that is attached to the OH group in compound A is a stereocenter and makes the compound A chiral. On the other hand, compound B does not have any asymmetric carbon.
8. A chiral compound with an ‘X’ group attached to the stereocenter has been replaced by a ‘Y’ group. The product obtained rotates the plane of polarised light in the direction opposite to that of the original compound. Name the process that has taken place.
a) Inversion
b) Retention
c) Racemisation
d) Inversion or retention
Answer: d
Clarification: Since the product rotates the plane of polarised light in some direction, it cannot be racemic. The product formed is a completely new compound from the original one and may have different or same optical behaviour as compared to the original compound.
9. The process of separation of a racemic mixture into the respective d and l optical isomers is called __________
a) racemisation
b) resolution
c) inversion
d) retention