Principles of stereochemistry: configurational and conformational isomerism - Question Bank

1. In a Fischer projection, vertical lines represent bonds going:
A) Towards the viewer (out of the plane).
B) Away from the viewer (towards the back).
C) In the plane of the paper.
D) Perpendicular to the plane of the paper.
2. In a Fischer projection, horizontal lines represent bonds coming:
A) Away from the viewer (towards the back).
B) Towards the viewer (out of the plane).
C) In the plane of the paper.
D) Parallel to the plane of the paper.
3. Fischer projections are commonly used to represent the stereochemistry of molecules with multiple chiral centers, particularly in:
A) Alkanes
B) Alkenes
C) Carbohydrates
D) Aromatic compounds
4. In carbohydrate chemistry, epimers that differ in configuration at the anomeric carbon are called:
A) Enantiomers
B) Epimers
C) Anomers
D) Diastereomers
5. Stereoisomers that differ in configuration at only one stereocenter are called:
A) Enantiomers
B) Epimers
C) Anomers
D) Diastereomers
6. Which of the following is an example of conformational isomerism?
A) 1,2-dichlorocyclopropane cis vs. trans
B) 2-butanol R vs. S
C) Cyclohexane chair vs. boat
D) Tartaric acid meso vs. enantiomers
7. Which of the following is an example of configurational isomerism?
A) Ethane staggered vs. eclipsed
B) Cyclohexane chair vs. boat
C) cis-2-butene vs. trans-2-butene
D) Butane anti vs. gauche
8. The 'E' configuration in the E/Z notation indicates:
A) Substituents with higher priority on the same side.
B) Substituents with higher priority on opposite sides.
C) Substituents with lower priority on the same side.
D) Substituents with lower priority on opposite sides.
9. The E/Z notation is a more unambiguous system for describing geometric isomerism, especially when there are more than two different substituents. 'Z' configuration corresponds to:
A) Substituents with higher priority on opposite sides.
B) Substituents with higher priority on the same side.
C) Substituents with lower priority on opposite sides.
D) Substituents with lower priority on the same side.
10. Which of the following can exhibit cis-trans isomerism?
A) Ethane
B) Propane
C) 1,2-dichlorocyclopropane
D) Methanol
11. In cis-trans isomerism, 'trans' refers to substituents that are:
A) On the same side of the double bond or ring.
B) On opposite sides of the double bond or ring.
C) In axial positions.
D) In equatorial positions.
12. In cis-trans isomerism, 'cis' refers to substituents that are:
A) On opposite sides of the double bond or ring.
B) On the same side of the double bond or ring.
C) In axial positions.
D) In equatorial positions.
13. Cis-trans isomerism is typically observed in compounds with:
A) Single bonds and free rotation.
B) Double bonds or in cyclic structures.
C) Chiral centers only.
D) Meso structures.
14. Geometric isomerism (cis-trans isomerism) is a type of stereoisomerism that arises due to:
A) Rotation about a single bond.
B) Restricted rotation about a double bond or in a ring.
C) The presence of a chiral center.
D) Mirror image relationships.
15. During a ring flip in cyclohexane, axial bonds become equatorial and vice versa. This is an example of interconversion between:
A) Enantiomers
B) Diastereomers
C) Configurational isomers
D) Conformational isomers
16. The interconversion of the chair conformations of cyclohexane by flipping the ring is called:
A) Rotation
B) Inversion
C) Ring flip
D) Epimerization
17. An equatorial bond in cyclohexane is oriented:
A) Perpendicular to the approximate plane of the ring.
B) Parallel to the approximate plane of the ring.
C) Above the ring.
D) Below the ring.
18. An axial bond in cyclohexane is oriented:
A) Parallel to the approximate plane of the ring.
B) Perpendicular to the approximate plane of the ring.
C) At an angle to the ring.
D) Within the plane of the ring.
19. In the chair conformation of cyclohexane, substituents can be in either axial or equatorial positions. Which position is generally more stable for a bulky substituent?
A) Axial
B) Equatorial
C) Both are equally stable
D) Depends on the other substituents
20. Cyclohexane exists predominantly in which conformation?
A) Boat
B) Twist-boat
C) Half-chair
D) Chair
21. The most stable conformation of n-butane is the:
A) Fully eclipsed
B) Gauche
C) Anti
D) Partially eclipsed
22. The 'anti' conformation of butane has a dihedral angle between the two methyl groups of:
A) 0 degrees
B) 60 degrees
C) 120 degrees
D) 180 degrees
23. The 'gauche' conformation of butane has a dihedral angle between the two methyl groups of:
A) 0 degrees
B) 60 degrees
C) 120 degrees
D) 180 degrees
24. In the eclipsed conformation of ethane, the dihedral angle between the hydrogen atoms on adjacent carbons is:
A) 0 degrees
B) 60 degrees
C) 120 degrees
D) 180 degrees
25. In the staggered conformation of ethane, the dihedral angle between the hydrogen atoms on adjacent carbons is:
A) 0 degrees
B) 60 degrees
C) 120 degrees
D) 180 degrees
26. Which conformation of ethane is the least stable?
A) Staggered
B) Eclipsed
C) Gauche
D) Anti
27. Which conformation of ethane is the most stable?
A) Eclipsed
B) Staggered
C) Skew
D) Partially eclipsed
28. The different spatial arrangements of a molecule that arise due to rotation about single bonds are called:
A) Configurational isomers
B) Conformational isomers
C) Geometric isomers
D) Stereoisomers
29. Conformational isomers are stereoisomers that:
A) Cannot be interconverted by rotation about single bonds.
B) Can be interconverted by rotation about single bonds.
C) Are mirror images of each other.
D) Are non-mirror images of each other.
30. Enantiomers and diastereomers are types of:
A) Constitutional isomers
B) Configurational isomers
C) Conformational isomers
D) Tautomers
31. Configurational isomers are stereoisomers that:
A) Can be interconverted by rotation about single bonds.
B) Cannot be interconverted by rotation about single bonds without breaking bonds.
C) Are mirror images of each other.
D) Are non-mirror images of each other.
32. Which of the following has a meso form?
A) 2,3-dichlorobutane
B) 2,3-butanediol
C) Tartaric acid
D) All of the above
33. A molecule with multiple chiral centers can be achiral if it possesses:
A) An enantiomeric relationship between the chiral centers.
B) A plane of symmetry (internal compensation).
C) A single chiral center.
D) A rotational axis of symmetry.
34. A meso compound is a stereoisomer that:
A) Is chiral and has a plane of symmetry.
B) Is achiral and has a plane of symmetry.
C) Is chiral and lacks a plane of symmetry.
D) Is achiral and lacks a plane of symmetry.
35. If, after assigning priorities, the lowest priority group is pointing away from the viewer and the sequence from highest to lowest is counterclockwise, the configuration is:
A) R
B) S
C) M
D) P
36. If, after assigning priorities, the lowest priority group is pointing away from the viewer and the sequence from highest to lowest is clockwise, the configuration is:
A) R
B) S
C) M
D) P
37. In the R/S system, the priority of substituents is determined by the:
A) Atomic number of the directly attached atom.
B) Molecular weight of the substituent.
C) Number of atoms in the substituent.
D) Electronegativity of the atom.
38. The R/S system is used to assign the absolute configuration of:
A) Diastereomers
B) Enantiomers
C) Meso compounds
D) Geometric isomers
39. A racemic mixture is optically:
A) Active
B) Inactive
C) Partially active
D) Strongly active
40. A mixture containing equal amounts of two enantiomers is called a:
A) Diastereomeric mixture
B) Meso mixture
C) Racemic mixture
D) Enantiomeric excess
41. Enantiomers have identical physical properties except for their interaction with:
A) Plane-polarized light
B) Non-chiral reagents
C) Acids
D) Bases
42. The relationship between two enantiomers is that they are:
A) Identical
B) Superimposable mirror images
C) Non-superimposable mirror images
D) Positional isomers
43. Which of the following is NOT a chiral molecule?
A) 2-butanol
B) Lactic acid
C) Methane
D) Alanine
44. A molecule that is superimposable on its mirror image is called:
A) Chiral
B) Achiral
C) Optically active
D) Enantiomerically pure
45. What is a chiral molecule?
A) A molecule that is superimposable on its mirror image.
B) A molecule that is non-superimposable on its mirror image.
C) A molecule with a plane of symmetry.
D) A molecule with an axis of symmetry.
46. A carbon atom bonded to four different atoms or groups is known as a:
A) Primary carbon
B) Secondary carbon
C) Tertiary carbon
D) Chiral center
47. Stereoisomers that are not mirror images of each other are called:
A) Enantiomers
B) Meso compounds
C) Diastereomers
D) Anomers
48. Stereoisomers that are non-superimposable mirror images of each other are called:
A) Diastereomers
B) Enantiomers
C) Meso compounds
D) Conformational isomers
49. Which type of isomerism involves different arrangements of atoms in space?
A) Structural isomerism
B) Stereoisomerism
C) Tautomerism
D) Positional isomerism
50. What is stereoisomerism?
A) Isomers that differ in the connectivity of atoms.
B) Isomers that have the same molecular formula but differ in the spatial arrangement of atoms.
C) Isomers that are non-superimposable mirror images of each other.
D) Isomers that have different functional groups.
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