2.2 Configurational Isomers

Question 1

Configurational isomers

Answer 1

can only change from on form to another by breaking and reforming covalent bonds

Question 2

2 categories of configurational isomers

Answer 2

enantiomers & diastereomers

(both are “optical isomers”)

Question 3

optical isomers

Answer 3

compounds with different spatial arrangement of groups which affects the rotation of plane-polarized light

Question 4

chiral compounds

Answer 4

a compound whose mirror image cannot be superimposed on the original compound

lack an internal plane of symmetry

Question 5

achiral compounds

Answer 5

have mirror images that CAN be superimposed

Question 6

chiral centers

Answer 6

carbon atoms with 4 different constituents (these are chiral carbons)

Question 7

characteristic of ALL chiral carbons

Answer 7

have 4 DIFFERENT groups connected

Question 8

enantiomers (4)

Answer 8

2 molecules that are nonsuperimposable mirror images of each other

same connectivity but opposite configurations at EVERY chiral center

same physical and chemical properties (except optical activity and reactions in chiral environments)

rotate plane polarized light to the same magnitude but opposite directions

Question 9

diastereomers

Answer 9

chiral molecules which have the same connectivity but are NOT mirror images of each other

must have multiple chiral centers (and differ at some but not all)

have different chemical properties

Question 10

optically active compounds

Answer 10

can rotate plane-polarized light

Question 11

optical activity

Answer 11

the rotation of plane polarized light by a chiral molecule

Question 12

dextrorotatory (d-) compounds

Answer 12

rotate plane-polarized light to the right (clockwise)

labelled (+)

Question 13

levorotatory (l-) compounds

Answer 13

rotate plane-polarized light to the left (counterclockwise)

labelled (-)

Question 14

how is d- vs l- determined

Answer 14

EXPERIMENTALLY!!!

it can NOT be determined from a molecules structure

it is NOT related to a molecules absolute configuration (R vs S)

Question 15

specific rotation formula

Answer 15

Question 16

standard concentration and path length for determining optical activity

Answer 16

concentration = 1 g/ml

path length = 1 dm (10 cm)

Question 17

racemic mixture

Answer 17

a mixture with equal concentrations of + and - enantiomers

no optical activity is observed (they “cancel” each other out)

will NOT rotate plane polarized light

Question 18

number of possible stereoisomers

for a molecule with n chiral centers

Answer 18

a molecule with n chiral centers has 2^n stereoisomers

ex. I and II are enantiomers, III and IV are enantiomers, the other pairs are diastereomers of one another

Question 19

cis-trans isomers (geometric isomers)

Answer 19

a subtype of diastereomers

substituents differ in their position around an immovable bond (ex. double bond) or a ring

cis: substituents are on the same side of the bond/ring
trans: substituents are on the opposite side of the bond/ring

Question 20

nomenclature used for polysubstitued double bonds

Answer 20

E / Z

Question 21

meso compounds

Answer 21

molecules that have chiral centers but are NOT optically active due to a plane of symmetry within the molecule

it IS superimposable on its mirror image