Stereochemistry Flashcards

A tetrahedral atom (usually carbon) bonded to four different substituents. Its presence typically makes a molecule chiral, except in meso compounds.

Non-superimposable mirror-image stereoisomers. They share all physical properties except the direction of optical rotation and behavior toward other chiral molecules.

Stereoisomers that are not mirror images. They differ at one or more (but not all) stereocenters and have different physical properties.

Assign CIP priorities (1-4) by atomic number. Orient priority 4 away from you. Trace 1-2-3: clockwise = R, counterclockwise = S.

A molecule with multiple chiral centers that is achiral due to an internal plane of symmetry. It is optically inactive and superimposable on its mirror image.

The ability of a chiral substance to rotate plane-polarized light. Clockwise = dextrorotatory (+), counterclockwise = levorotatory (-). Direction cannot be predicted from R/S.

[a] = a / (l x c), where a = observed rotation (degrees), l = path length (dm), c = concentration (g/mL). Reported at 20 degrees C, 589 nm.

A 1:1 mixture of enantiomers showing zero net optical rotation. Denoted (+-) or (d,l).

ee = |%R - %S|, or equivalently |observed rotation / pure rotation| x 100%. 100% ee = pure enantiomer; 0% ee = racemate.

Horizontal bonds point toward the viewer (wedge), vertical bonds point away (dash). Most oxidized carbon at top. May rotate 180 degrees but not 90 degrees.

If priority 4 is on a vertical bond, read 1-2-3 directly (CW = R, CCW = S). If on a horizontal bond, read 1-2-3 and reverse the assignment.

No. R can be (+) or (-), and same for S. Optical rotation is an experimental property independent of the R/S label.

2^n. Actual count may be lower if meso compounds exist.

Diastereomers from restricted rotation (double bond or ring). Cis = same-side groups; trans = opposite-side groups. Complex cases use E/Z.

Apply CIP priorities to each double-bond carbon. Higher-priority groups on the same side = Z (zusammen); opposite sides = E (entgegen).

Diastereomers differing at only one of multiple stereocenters. Common in carbohydrate chemistry (e.g., glucose and galactose are C-4 epimers).

The carbon from the open-chain carbonyl that becomes a new stereocenter upon cyclization of a sugar. It generates alpha and beta anomers.

Conformational isomers interconvert by bond rotation and are generally not isolable. Configurational isomers (enantiomers, diastereomers) require bond breaking and are isolable.

Equatorial placement avoids 1,3-diaxial interactions (steric strain with axial hydrogens on the same face), lowering the overall energy.

An sp3 carbon with two identical and two different substituents. Replacing one identical group creates a chiral center. Enzymes can distinguish the two identical groups.

Complete inversion of configuration at a carbon during SN2. Backside attack by the nucleophile flips the remaining substituents, converting R to S or vice versa.

The product keeps the same spatial arrangement as the starting material. Occurs when the stereocenter is not involved in bond changes or via double inversion (e.g., neighboring group participation).

A reaction where a specific stereoisomer of starting material gives a specific stereoisomeric product. Examples: SN2 (always inversion), E2 (anti-periplanar geometry).

A reaction where one stereoisomeric product forms preferentially from a single starting material. Example: hydroboration-oxidation gives syn addition.

Stereoisomerism from restricted single-bond rotation with a high enough barrier to isolate the conformers. Classic example: biphenyls with bulky ortho substituents (axial chirality).