Chapter 5: Stereochemistry

isomer

2 compounds w/same formula but different arrangements

constitutional isomer

different atomic arrangement 

• order or dif. functional groups

• different bond connectivity

stereoisomers

different 3D configuration

enantiomers

mirror-images

• non-superimposable stereoisomers

• chiral centers have opposite configurations (R vs S)

• all chiral centers are inverted = mirror images

diastereoisomers

non-mirror images

• non-superimposable stereoisomers 

• only one chiral center needs to be inverted 

epimers

diastereomers that differ at only one chiral center (R or S differs, not elements that make up molecule)

configurational diastereomers

cis/trans diastereomers

carbon must be bonded to 2 dif. things

• cis: same side

• trans: opposite sides

chirality

atom must have 4 different things attached to it

• groups are considered “different” if there is any structural variation (if groups could not be superimposed if detached, they are different)

Chirality center

a point in a molecule where 4 different groups are attached to carbon 

optical activity

If it has a chiral center → optical activity (will rotate the light)

achiral

molecule w/plane of symmetry is the same as its mirror image 

• optically inactive 

plane of symmetry 

divides an entire molecule into 2 pieces that are exact mirror images 

• If an object has a plane of symmetry it is the same as its mirror image 

E

higher-priority groups on opposite sides

• “trans”

Z

higher-priority groups on same sides

• “cis”

meso compound

achiral compound w/chirality centers

• plane of symmetry in middle

• at least 2 chiral centers, each carbon is attached to the same 4 different things on both sides

• one has to be R and other is S

racemic mixture

50:50 mixture of 2 chiral compounds, one R and one S

• optical activity comes out to zero