Organic Chemistry -Structural Isomers
-Stereoisomers
Test Study Guide: -Relative and Absolute
Configurations
Ch.2 ISOMERS -And More
CONCEPT SUMMARY
Structural Isomers
Share only a molecular formula.
Exhibit different physical and chemical properties.
Stereoisomers
Conformational Isomers: Differ by rotation around a single (σ) bond.
Staggered Conformations:
i. Groups are 60° apart in Newman projections.
ii. Anti Staggered: Two largest groups are 180° apart, minimizing strain.
iii. Gauche Staggered: Two largest groups are 60° apart, introducing some strain.
Eclipsed Conformations:
i. Groups are directly in front of each other in Newman projections.
ii. Totally Eclipsed: Two largest groups are directly aligned, maximizing strain.
Strain in Cyclic Molecules:
Comes from:
i. Angle Strain: Due to stretching or compressing angles from their normal size.
ii. Torsional Strain: From eclipsing conformations.
iii. Nonbonded Strain: From interactions between substituents on nonadjacent carbons.
Cyclic molecules typically adopt nonplanar shapes to minimize these strains.
Substituents in Cyclohexane:
Substituents on cyclohexane can be classified as axial(pointing up or down from the molecular plane) or
equatorial(in the plane of the molecule).
Axial substituents create increased nonbonded strain due to steric interactions.
Positioning of Substituents:
In cyclohexane molecules with multiple substituents, the largest substituent typically occupies the equatorial
position to minimize steric strain and enhance stability.
Configurational Isomers:
Configurational isomers can only be interconverted by breaking and reforming bonds, indicating that their
spatial arrangement is fixed unless chemical bonds are altered.
Enantiomers:
-Stereoisomers
Test Study Guide: -Relative and Absolute
Configurations
Ch.2 ISOMERS -And More
CONCEPT SUMMARY
Structural Isomers
Share only a molecular formula.
Exhibit different physical and chemical properties.
Stereoisomers
Conformational Isomers: Differ by rotation around a single (σ) bond.
Staggered Conformations:
i. Groups are 60° apart in Newman projections.
ii. Anti Staggered: Two largest groups are 180° apart, minimizing strain.
iii. Gauche Staggered: Two largest groups are 60° apart, introducing some strain.
Eclipsed Conformations:
i. Groups are directly in front of each other in Newman projections.
ii. Totally Eclipsed: Two largest groups are directly aligned, maximizing strain.
Strain in Cyclic Molecules:
Comes from:
i. Angle Strain: Due to stretching or compressing angles from their normal size.
ii. Torsional Strain: From eclipsing conformations.
iii. Nonbonded Strain: From interactions between substituents on nonadjacent carbons.
Cyclic molecules typically adopt nonplanar shapes to minimize these strains.
Substituents in Cyclohexane:
Substituents on cyclohexane can be classified as axial(pointing up or down from the molecular plane) or
equatorial(in the plane of the molecule).
Axial substituents create increased nonbonded strain due to steric interactions.
Positioning of Substituents:
In cyclohexane molecules with multiple substituents, the largest substituent typically occupies the equatorial
position to minimize steric strain and enhance stability.
Configurational Isomers:
Configurational isomers can only be interconverted by breaking and reforming bonds, indicating that their
spatial arrangement is fixed unless chemical bonds are altered.
Enantiomers:
