04 Conformation and Stereochemistry Free Online FlashCards

What distinguishes stereoisomers?

Stereoisomers have the same atom-to-atom connectivity but differ in the spatial arrangement of their atoms.

What is a molecular conformation?

A conformation is a spatial arrangement reached by rotation around formally single bonds.

Why is an eclipsed conformation generally higher in energy?

Eclipsed bonds generally have higher energy than staggered bonds because eclipsing creates torsional strain.

How do anti and gauche arrangements differ in butane?

In butane, anti places the methyl groups 180° apart; gauche places them 60° apart. The anti arrangement is more stable.

What changes and what stays the same in a cyclohexane chair flip?

A chair flip exchanges each substituent’s axial and equatorial positions while preserving whether it points up or down.

Why do larger substituents usually favor equatorial positions on cyclohexane?

Larger substituents usually favor equatorial positions because axial positions create steric interactions.

How does changing configuration differ from changing conformation?

Changing configuration generally requires breaking bonds or overcoming a barrier that prevents free rotation, unlike ordinary conformational interconversion.

What makes a molecule chiral?

A molecule is chiral if it is not superimposable on its mirror image. A tetrahedral carbon attached to four different groups is a common chirality center, but chirality is a property of the whole molecule.

What are enantiomers?

Enantiomers are stereoisomers that are nonsuperimposable mirror images of each other.

How do enantiomers differ in optical rotation?

In an achiral environment, enantiomers have the same ordinary physical properties but rotate plane-polarized light in opposite directions. An R or S descriptor does not predict the rotation’s sign.

What distinguishes diastereomers from enantiomers?

Diastereomers are stereoisomers that are not mirror images. They can differ in physical properties and chemical behavior, even in achiral environments.

What is a meso compound?

A meso compound has stereogenic centers but is achiral overall because of molecular symmetry.