Stereoisomers are compounds that have
A same molecular formula but different functional groups
B same molecular formula but different connectivity
C same molecular formula and same connectivity but different spatial arrangement
D different molecular formula
Stereoisomers differ only in 3-D arrangement of atoms.
Optical isomerism arises due to
A plane of symmetry
B centre of symmetry
C chirality
D conjugation
A chiral molecule is non-superimposable on its mirror image.
A chiral carbon is one which is attached to
A four identical groups
B three identical and one different group
C four different groups
D two identical and two different groups
Such a carbon is asymmetric and shows optical activity.
Which molecule is optically active
A CH₃–CH₂–CH₃
B CH₃–CH(OH)–CH₂–CH₃
C CH₃–CO–CH₃
D CH₂=CH₂
The second carbon is chiral (four different groups).
Enantiomers are
A diastereomers
B identical compounds
C non-superimposable mirror images
D geometrical isomers
Enantiomers differ only in spatial orientation.
Enantiomers have identical
A optical rotation
B melting point
C boiling point
D both B and C
Physical properties are same except direction of optical rotation.
A racemic mixture is
A optically active
B optically inactive due to internal compensation
C optically inactive due to external compensation
D chiral
Equal amounts of (+) and (−) enantiomers cancel rotation.
The symbol (+) indicates
A clockwise rotation of plane-polarized light
B anticlockwise rotation
C R-configuration
D S-configuration
(+) denotes dextrorotation, not configuration.
Which instrument is used to measure optical rotation
A spectrometer
B polarimeter
C colorimeter
D refractometer
It measures angle and direction of rotation of plane-polarized light.
Which compound shows internal compensation
A racemic mixture
B meso compound
C enantiomer
D diastereomer
Meso compounds have plane of symmetry.
A meso compound is
A chiral and optically active
B achiral but optically active
C achiral and optically inactive
D always racemic
Internal symmetry causes cancellation.
Diastereomers differ in
A connectivity
B mirror image relation
C configuration at one or more chiral centers but not all
D molecular formula
They are not mirror images.
Which pair represents diastereomers
A (+)- and (−)-lactic acid
B cis- and trans-2-butene
C CH₄ and C₂H₆
D R- and S-glyceraldehyde
They are stereoisomers but not mirror images.
Geometrical isomerism arises due to
A free rotation about C–C bond
B restricted rotation
C presence of chiral carbon
D resonance
Seen in alkenes due to C=C bond.
Which compound shows geometrical isomerism
A ethene
B propene
C but-2-ene
D methane
Restricted rotation and different substituents on C=C.
Cis-isomer generally has
A lower dipole moment
B higher dipole moment
C same dipole moment as trans
D zero dipole moment
In cis, dipoles add; in trans, they cancel.
Which is more stable
A cis-2-butene
B trans-2-butene
C both equal
D ethene
Less steric hindrance in trans-form.
Optical activity depends on
A temperature only
B pressure only
C molecular asymmetry
D molecular weight
Asymmetry causes chirality.
Number of optical isomers for a compound with one chiral carbon is
A 1
B 2
C 3
D 4
One chiral center → two enantiomers.
Maximum number of stereoisomers for n chiral centers is
A n²
B 2ⁿ
C n!
D 2n
General formula for stereoisomers.
Different spatial arrangements obtained by rotation about single bond are called
A configurations
B isomers
C conformations
D enantiomers
Single bond rotation gives conformers.
Ethane conformations differ due to rotation about
A C=C bond
B C–C single bond
C C–H bond
D π-bond
Free rotation possible around σ-bond.
The most stable conformation of ethane is
A eclipsed
B staggered
C gauche
D skew
Minimum torsional strain.
Eclipsed conformation is unstable due to
A angle strain
B torsional strain
C steric strain only
D ring strain
Electron repulsion between bonds.
Energy difference between staggered and eclipsed ethane is due to
A resonance
B hyperconjugation
C inductive effect
D hydrogen bonding
Better hyperconjugation in staggered form.
In Newman projection, front carbon is represented by
A dot
B circle
C square
D triangle
Dot = front carbon; circle = rear carbon.
Butane shows maximum number of conformations equal to
A 2
B 3
C 4
D many
Continuous rotation gives infinite conformations.
The most stable conformation of butane is
A eclipsed
B gauche
C anti
D skew
CH₃ groups are farthest apart.
Gauche conformation of butane is less stable due to
A torsional strain only
B steric strain between CH₃ groups
C angle strain
D ring strain
Methyl groups come closer.
Which conformation has highest energy in butane
A anti
B gauche
C eclipsed (CH₃–H)
D fully eclipsed (CH₃–CH₃)
Maximum steric and torsional strain.
Cyclohexane adopts chair conformation because
A it is planar
B it minimizes strain
C it maximizes angle strain
D it has π-bonds
Chair has minimum torsional and angle strain.
In cyclohexane chair, axial bonds are
A parallel to ring plane
B perpendicular to ring plane
C inclined at 60°
D random
Axial bonds are vertical.
Equatorial bonds are
A perpendicular to plane
B parallel to plane
C inclined outward
D always upward
They lie roughly along ring plane.
1,3-diaxial interaction causes
A angle strain
B steric strain
C torsional strain
D ring strain
Axial substituents interact sterically.
Bulky substituent in cyclohexane prefers
A axial position
B equatorial position
C either position equally
D bridge position
Minimizes 1,3-diaxial interactions.
Ring flip in cyclohexane interconverts
A axial ↔ equatorial
B cis ↔ trans
C R ↔ S
D chair ↔ boat
Positions swap during ring inversion.
Boat conformation of cyclohexane is unstable due to
A angle strain only
B torsional strain only
C steric repulsion and torsional strain
D resonance
Flagpole interaction and eclipsing bonds.
Which conformation has minimum energy in cyclohexane
A chair
B boat
C twist boat
D planar
Almost strain-free.
Optical isomers rotate plane-polarized light due to
A resonance
B asymmetry
C conjugation
D hyperconjugation
Lack of symmetry causes rotation.
Which is optically inactive
A chiral compound
B enantiomer
C racemic mixture
D pure (+) compound
External compensation cancels rotation.
Plane of symmetry makes a compound
A chiral
B optically active
C achiral
D dextrorotatory
Symmetry destroys chirality.
Which compound has zero optical rotation
A pure enantiomer
B meso compound
C chiral compound
D R-isomer
Internal compensation.
A compound having two chiral centers may have meso form if
A centers are identical
B molecule has plane of symmetry
C both centers are R
D both centers are S
Symmetry causes internal compensation.
Cis–trans isomerism is also called
A optical isomerism
B structural isomerism
C geometrical isomerism
D conformational isomerism
Due to geometry around double bond.
Which has greater boiling point
A cis-isomer
B trans-isomer
C both same
D depends on solvent
Higher dipole moment → stronger intermolecular forces.
Newman projection is used to study
A optical isomerism
B geometrical isomerism
C conformations
D resonance
Shows different rotational forms.
Which interaction destabilizes axial methyl group in cyclohexane
A torsional strain
B angle strain
C 1,3-diaxial interaction
D resonance
Steric repulsion with axial hydrogens.
Cyclopropane is unstable due to
A torsional strain
B angle strain
C steric strain
D resonance
Bond angles deviate from 109.5°.
Optical activity is measured in
A degrees
B joules
C pascal
D tesla
Rotation angle is measured in degrees.
Correct statement is
A Conformations are isolable
B Enantiomers have different physical properties
C Chair form is most stable cyclohexane
D Cis isomer always more stable
Chair minimizes all types of strain.