MCAT Organic Chemistry

Fischer Projections

Vertical lines in

Horizontal lines out

Newman Projection Stability Order

Anti > Gauche > Eclipsed

Chirality

The “handedness” of a molecule

Stereoisomers

Two forms of a molecule that differ by their stereochemistry

+/- or d/l system

ONLY at chiral centers

+/- or d/l system

How the molecules bends plane-polarized light

Clockwise: d- or +, dextro

Counterclockwise: l- or -, levo-

Chiral Center

4 different substituents

Requires asymmetry

NO chiral center if:

• Double bond

• Triple bond

• 2 or more of the same substituents

Cahn-Ingold-Prelog Rules

1. Higher atomic number = higher priority

2. If there is a tie, the tie winner is the one with the highest number substituent

3. If there is still a tie, move to the next atom down the chain, then 4, 5 etc. until tie is broken

4. Double bonds count as two bonds to a atom of the same atomic number; double bond to an atom will win a tie vs a single bond to the same atom. Triple bonds count as 3 and win over double bonds similarly

5. The heavier isotope wins the ties if we have two of the same element

S Configuration

Sinister / LEFT

R Configuration

Rectus / RIGHT

When lowest priority atom is point out at you:

Determine the direction of the arrow (S or R), then flip it to the other one

• If it was R, then answer would be S and vice versa

B. R, S