Molecular flexibility

Skeletal to Newman

Look directly down a specific carbon-carbon bond. Carbon closer to viewing point is front carbon. Identify three bonds attached to it. Place the group point up or down in the plane accordingly. Wedged/dashed groups point away from each other. Repeat for rear carbon. Arrange substituents in staggered or eclipsed.

Skeletal to Fischer

Orient main carbon chain vertically with most oxidized carbon at the top. Determine absolute configurations (R/S) for each chiral center. Orient carbon backbone vertically. Align substituents (horizontal = out, vertical = in). Verify using R/S configurations.

R/S labeling

Rank atoms around chiral center based on atomic number (more mass = higher priority). Orient lowest priority group so it points straight back into paper. Trace path from 1-2-3. Clockwise = R, counterclockwise = S. If #4 points out of paper, reverse final result

Conformation

Spatial arrangement of atoms that results from rotation around single covalent bonds

Staggered vs eclipsed

Staggered is low energy, bonds are as far apart as possible. Eclipsed is high energy, bonds align closely and repel. Conformations with less crowding/repulsion have lower potential energy and higher stability

Chair conformation

Most stable, lowest-energy 3D shape a ring can adopt. No strain, ideal angles, staggered bonds. Each atom holds two substituents in axial (perpendicular to ring) and equatorial (in plane of ring)

Chair flip

Carbon atoms convert equatorial to axial and vice versa. Bulky substituents more stable in equatorial, axial crowds due to steric strain.

Steric interactions

Obstructions caused by the size of neighboring groups/atoms

Torsional interactions

Repulsive forces between the bonding electrons of neighboring atoms

Hydrogens are too small for steric interactions

True

Methyl groups are too small for steric interactions

False

Eclipsed conformation

Bonds on adjacent carbons line up directly behind each other. Maximum torsional strain and higher energy

Staggered conformation

Bonds on adjacent carbons sit as far apart as possible. Minimum energy and maximum stability

Gauche conformation

A staggered arrangement where bulky groups sit 60° apart. Higher energy than anti

Anti conformation

A staggered arrangement where bulky groups sit 180° from each other. Most stable and lowest energy

Boat conformation

Less stable cyclic conformation, hydrogens crowd by pointing in same direction on opposite ends of the ring

Stereocenter / chiral center

Any point in a molecule where swapping two groups creates a new stereoisomer. Most commonly an sp³ carbon bonded to four unique groups.