Isomers

Question 1

Structural isomers (constitutional)

Answer 1

• Same molecular formula, different structure
• different chemical and physical properties

Question 2

Physical properties

Answer 2

Don’t change the composition of matter, such as melting point, boiling point, solubility, odor, color, and density

Question 3

Chemical properties

Answer 3

Have to do with reactivity of the molecules and result in changes in chemical composition. Generally dictated by functional groups

Question 4

Stereoisomers

Answer 4

Have same structural backbone but differ in how atoms are arranged in space.

For any molecule with n chiral centers, there are 2ⁿ possible stereoisomers.

Question 5

Conformational isomers

Answer 5

• Are the same molecule but just differ at points in their natural rotation around single bonds

Question 6

Straight chain conformations

Answer 6

• anti and gauche conformers
• ​Favors most stable conformer

Question 7

Cyclic conformations

Answer 7

• Stability depends on ring strains: angle strain, torsional strain, steric strain
  cyclobutane: puckered (v-shaped)
  cyclopentane: envelope
  cyclohexane: chair, boat, twist-boat

Question 8

Angle Strain

Answer 8

Results when bond angles deviate from their ideal values by being stretched or compressed.

Question 9

Torsional Strain

Answer 9

Results when cyclic molecules must assume conformations that have eclipsed or gauche interactions.

Question 10

Steric strain

Answer 10

Results when nonadjacent atoms or groups compete for the same space

Question 11

Configuration isomers

Answer 11

Can only change from one form to another by breaking and reforming covalent bonds.

• entantiomers and diastereomers

Question 12

chiral

Answer 12

• mirror image cannot be superimposed on the original object
• NO plane of symmetry
• 4 different substituents bound to central carbon

Question 13

enantiomers

Answer 13

nonsuperimposable mirror images

Question 14

Diastereomers

Answer 14

• These molecules are chiral and share the same connectivity, but are not mirror images of each other.
• Differ at some, but not all stereogenic centers

Question 15

Racemic mixture

Answer 15

• When both enantiomers are in equal conecntraions.
• the rotations of plane-polarized light cancels out and no optical activity is observed

Reacting two enantiomers with a single enantiomer of antoehr compound will, by definition, lead to two diastereomers.

Question 16

Cis-trans isomers

Answer 16

Type of diasteromers in which substituents differ in their position around an immovable bond, such as a double bond, or around a ring structure.

Question 17

Meso compound

Answer 17

A molecule with chiral centers that has an internal plane of symmetry.

• molecular equivalent of a racemic mixture

Question 18

Relative configuration

Answer 18

the configuration of a chiral molecule in relation to another chiral molecule.

• Use to determine if molecules are enantiomers, diastereomers, or the same molecule

Question 19

Absolute conformation

Answer 19

describes teh exact spatial arrangement of these atoms or groups, independent of other molecules

Question 20

E & Z

Answer 20

Used for compounds with polysubstituted double bonds. Priority is assigned based on the atom bonded to double-bonded carbons

• Higher the atomic number, the higher the priority

Question 21

R and S

Answer 21

Used for chiral (stereogenic) centers in molecules.

1. Assign priority; highest atomic number
2. Orient so lowest priority is in back
   
   1. Or swap group facing back with lowest priority
   2. Any time two groups are switched on a chiral carbon, the stereochemistry is inverted.
3. Draw a circle
4. Write the name

Question 22

Finding R & S in Fischer Projections

Answer 22

1. Move the lowest-priority group into the correct position (facing away)
2. Switch the other two groups as well.
3. molecule will have same designation as the initial molecule.