Ch 2 - Isomers

Question 1

Structural or constitutional isomers

Answer 1

The most different. They only share molecular (ex C6H14) formula

Question 2

Physical properties

Answer 2

Color, odor, density, boiling point, melting point , solubility
Characteristics of processes that don’t change the composition of matter

Question 3

Chemical properties

Answer 3

Reactivity of molecule with other molecules results in change in composition

Question 4

Stereoisomers

Answer 4

Same chemical formula
Same atomic connectivity (same structural backbone)
All isomers that are not constitutional fall in this category
Broken down into conformational and configurational

Question 5

Conformational isomers

Answer 5

Also called conformers
The most similar isomers
Same molecule at different points in their natural rotation around a sigma bond.

Question 6

Staggered conformation

Answer 6

Newman projection - along the line of site - there is no overlap except for the unavoidable Cs that are directly in front and behind each other

Question 7

Anti conformation

Answer 7

Type of staggered conformation that is most energetically favored
Two largest groups are antiperiplanar (in the same plane but on opposite sides)

Question 8

Gauche

Answer 8

Type of staggered conformation where the two largest groups are 60 degrees from each other

Question 9

Eclipsed conformation

Answer 9

Eclipsed is two methyl groups are 120 degrees apart and overlap with the hydrogen atoms
When the methyl groups directly overlap it is totally eclipsed. Least favorable energetically because two largest groups are synperiplanar (same plane, same side)

Question 10

Ring strain

Answer 10

Arises from three factors:
Angle strain - bond angles deviate form ideal by being stretched or compressed
Torsional strain - cyclic molecules must assume eclipsed or gauche conformations
Non bonded strain (van der waals repulsion) - nonadjacent atoms or groups compete for same space

Question 11

Equatorial

Answer 11

Over

Parallel

Question 12

Axial

Answer 12

Up and down

Question 13

Configurational isomers

Answer 13

Can only change from one form to another by breaking and reforming covalent bonds.
Two types - enantiomers and diastereomers, both also called optical isomers

Question 14

Chirality

Answer 14

Object is chiral if its mirror image cannot be superimposed

Lacks internal plane of symmetry

Question 15

Enantiomers

Answer 15

Nonsuperimposable mirror images of each other.
Same connectivity but opposite configurations at every chiral center
Identical physical and chemical properties except for optical activity and reactions in chiral environments

Question 16

Optical activity

Answer 16

Rotation of plane polarized light by a chiral molecule. Direction Only determined through experiment
Rotation to right or clockwise is dextrorotatory (d) and is labeled +
Rotation to left or counter is levorotatory (l) or -

Question 17

Specific rotation

Answer 17

[alpha]=alpha sub obs/(c times l) 
[alpha] is specific rotation in degrees 
Alpha sub obs is observed rotation in degrees 
C is the concentration in g/ml 
l is the path length in dc (10 cm)

Question 18

Racemic mixture

Answer 18

When both + and - enantiomers exist in equal concentrations together

Question 19

Diastereomers

Answer 19

Non-mirror image configurational isomers

Differ at some but not all of their necessarily multiple chiral (stereogenic) centers

Question 20

Cis-trans isomers

Answer 20

Also geometric isomers
Substituents differ in their position around an immovable bond
Same side of bond = cis
Different = trans

Question 21

Meso compounds

Answer 21

Compounds with chiral centers within but also containing an internal plane of symmetry and therefore having no optical activity

Question 22

Relative configuration

Answer 22

Chiral molecule’s configuration in relation to another chiral molecule (often through chemical inter conversion)

Question 23

Absolute confirmation

Answer 23

Describes exact spatial arrangement of atoms or groups independent of other molecules

Question 24

E and Z forms

Answer 24

Polysubstituted compounds
Identify highest priority substituent attached to each double bonded carbon by atomic number or neighboring atomic number
If substituents are on same side it’s Z if not, E

Question 25

Chan-Ingold-Prelog priority rules

Answer 25

Priority is based on highest atomic number. If tied then priority is given to next atom outward until they do not tie anymore.