Principles of stereochemistry: configurational and conformational isomerism - One Line Questions

1. In the staggered conformation of ethane, the dihedral angle between the hydrogen atoms on adjacent carbons is: — 180 degrees
2. In the eclipsed conformation of ethane, the dihedral angle between the hydrogen atoms on adjacent carbons is: — 0 degrees
3. The 'gauche' conformation of butane has a dihedral angle between the two methyl groups of: — 60 degrees
4. The 'anti' conformation of butane has a dihedral angle between the two methyl groups of: — 180 degrees
5. Which of the following is an example of conformational isomerism? — Cyclohexane chair vs. boat
6. Which of the following is NOT a chiral molecule? — Methane
7. Which of the following has a meso form? — All of the above
8. What is a chiral molecule? — A molecule that is non-superimposable on its mirror image.
9. A racemic mixture is optically: — Inactive
10. Fischer projections are commonly used to represent the stereochemistry of molecules with multiple chiral centers, particularly in: — Carbohydrates
11. A molecule with multiple chiral centers can be achiral if it possesses: — A plane of symmetry (internal compensation).
12. In the R/S system, the priority of substituents is determined by the: — Atomic number of the directly attached atom.
13. In a Fischer projection, horizontal lines represent bonds coming: — Towards the viewer (out of the plane).
14. 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? — Equatorial
15. Cyclohexane exists predominantly in which conformation? — Chair
16. Configurational isomers are stereoisomers that: — Cannot be interconverted by rotation about single bonds without breaking bonds.
17. Conformational isomers are stereoisomers that: — Can be interconverted by rotation about single bonds.
18. A molecule that is superimposable on its mirror image is called: — Achiral
19. The different spatial arrangements of a molecule that arise due to rotation about single bonds are called: — Conformational isomers
20. Enantiomers and diastereomers are types of: — Configurational isomers
21. A mixture containing equal amounts of two enantiomers is called a: — Racemic mixture
22. Stereoisomers that are non-superimposable mirror images of each other are called: — Enantiomers
23. The R/S system is used to assign the absolute configuration of: — Enantiomers
24. Which conformation of ethane is the most stable? — Staggered
25. Stereoisomers that are not mirror images of each other are called: — Diastereomers
26. During a ring flip in cyclohexane, axial bonds become equatorial and vice versa. This is an example of interconversion between: — Conformational isomers
27. Stereoisomers that differ in configuration at only one stereocenter are called: — Epimers
28. In carbohydrate chemistry, epimers that differ in configuration at the anomeric carbon are called: — Anomers
29. Which of the following can exhibit cis-trans isomerism? — 1,2-dichlorocyclopropane
30. Which of the following is an example of configurational isomerism? — cis-2-butene vs. trans-2-butene
31. The most stable conformation of n-butane is the: — Anti
32. The relationship between two enantiomers is that they are: — Non-superimposable mirror images
33. A meso compound is a stereoisomer that: — Is achiral and has a plane of symmetry.
34. What is stereoisomerism? — Isomers that have the same molecular formula but differ in the spatial arrangement of atoms.
35. In cis-trans isomerism, 'cis' refers to substituents that are: — On the same side of the double bond or ring.
36. In cis-trans isomerism, 'trans' refers to substituents that are: — On opposite sides of the double bond or ring.
37. An axial bond in cyclohexane is oriented: — Perpendicular to the approximate plane of the ring.
38. An equatorial bond in cyclohexane is oriented: — Parallel to the approximate plane of the ring.
39. Enantiomers have identical physical properties except for their interaction with: — Plane-polarized light
40. A carbon atom bonded to four different atoms or groups is known as a: — Chiral center
41. 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: — R
42. 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: — S
43. The interconversion of the chair conformations of cyclohexane by flipping the ring is called: — Ring flip
44. Geometric isomerism (cis-trans isomerism) is a type of stereoisomerism that arises due to: — Restricted rotation about a double bond or in a ring.
45. Cis-trans isomerism is typically observed in compounds with: — Double bonds or in cyclic structures.
46. Which conformation of ethane is the least stable? — Eclipsed
47. Which type of isomerism involves different arrangements of atoms in space? — Stereoisomerism
48. 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: — Substituents with higher priority on the same side.
49. The 'E' configuration in the E/Z notation indicates: — Substituents with higher priority on opposite sides.
50. In a Fischer projection, vertical lines represent bonds going: — Away from the viewer (towards the back).
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