Organic Chemistry

Conformations 

Lower energy = staggered = more stable 

Anti I = 0° & 360° 

 

Gauche III = 120° 

 

Gauche V =240° 

 

Higher energy= eclipsed =less stable 

Eclipsed II =60° 

 

Eclipsed IV = 180° 

 

Eclipsed VI = 300° 

cyclohexanes: 

Chair conformation → most stable 

 

 

 

 

Vertical orientation = axial, other = equatorial 

Heavier substituent = equatorial  

Boat conformation → less stable than chair 

 

Isomerism: 

Conformers: same molecule → differs in angle about 1 or more sigma 

Isomers: molecular formula CHNO  

Constitutional isomers: same molecular formula ; different compounds W/ different names 

Different connectivity 

Stereoisomers: same connectivity 

i.e. Cis vs trans, Z vs E 

Z vs E: 

Z = both high priority on same side 

E = high priority on diff sides 

Cahn-Ingold-Prelog Sequence Rules 

"rules to assign priority" 

  1. higher atomic # = higher priority 

  2.  if atoms are identical move onto next atom until a difference is found  

  3. Double and triple bonds = treated as single atoms are duplicated or triplicated accordingly  

Enantiomers aka optical isomers 

Chiral centers 

non-superimposable mirror images 

Optically active: rotate plane of plane polarized light in opposite directions 

(-) = counterclockwise rotation → dextrorotatory 

(+) = clockwise rotation →levorotatory 

Raceme mixture: equal parts + & - enantiomers of a chiral substance → optically inactive 

Equal but opposite specific rotation 

2+ asymmetric carbon atoms = 2^n isomers 

Diastereoisomers = non-mirror images 

Chiral centers 

Configurational diastereoisomers 

Two compounds w/ same connectivity but differ in 3-d structure at some of their stereocenters 

Cis vs trans, E vs Z; geometric isomers  

Meso compound: not optically active → 2 apparent 'asymmetric carbons' → plane of symmetry