Chapter Summary And Cheat Sheet

Chapter 5 Summary & Cheat Sheet

Chirality: A molecule is chiral if not superimposable on its mirror image. Often arises from an sp³ center with four different substituents.
Enantiomers: Non-superimposable mirror images; all stereocenters inverted. Identical physical properties in achiral media, opposite optical rotations.
Diastereomers: Stereoisomers not related as mirror images (some but not all centers inverted, or cis/trans differences). Different physical properties.
Meso: Multiple stereocenters but overall achiral due to an internal mirror plane; optically inactive.
R/S assignment: Rank substituents (atomic number), orient lowest priority back, trace 1→2→3 (clockwise = R, counterclockwise = S). For Fischer, vertical bonds go back, horizontal come out.

Racemate (±): 50:50 enantiomer mix; optically inactive.
Enantiomeric excess (ee): |R−S|/(R+S) × 100%; optical rotation scales with ee.
Fischer projections: 2D shorthand; only 180° rotation preserves the same molecule. A 90° rotation depicts the enantiomer.

Enantiomers: all centers opposite; mirror images; same physical properties (except optical rotation sign).
Diastereomers: some centers differ; not mirror images; different properties.
Meso: internal plane; identical to mirror image; achiral.
Identical: same connectivity and same R/S at every center.
Constitutional isomers: different connectivity (not stereoisomers).

Count possible stereoisomers: up to 2ⁿ, reduced if meso.
To test enantiomers, invert all centers of one structure and compare; if matches, they’re enantiomers. If only some match, diastereomers; if all match, identical.
Use models or mirror drawings to verify tricky cases (meso vs enantiomer pairs, cyclic cis/trans).