Staff Site Universitas Negeri Yogyakarta KO II Stereokimia

Chapter 6

Isomers and Stereochemistry

Essential Organic Chemistry

Paula Yurkanis Bruice

Review of Isomerism



Isomers

–

Compounds that have the same

molecular formula but do not have identical

structures.



Constitutional Isomers

–

differ in the way

their atoms are connected.

6.1 Cis-trans isomers



Cyclic structure

.

6.2 Chirality



Chiral

–

Nonsuperimposable on its

mirror image

.



Achiral

–

Superimposable

on its mirror image

.



If a molecule (or object) has

a

mirror plane

or an

Chiral or Achiral?



Brandy snifter

Chiral or Achiral?



Shears

Chiral or Achiral?



Beer mug

Chiral or Achiral?



Hiking boot

Chiral or Achiral?



Baseball glove

Chiral or Achiral?



Boat propeller

Chiral or Achiral?



Desk chair

Chiral or Achiral?



School desk

Chiral or Achiral?



cis-1,3-dimethylcyclopentane

Chiral or Achiral?



trans-1,3-dimethylcyclopentane

Chiral or Achiral?



1,1-dimethylcyclohexane

6.3 Asymmetric centers

Chiral or Achiral?

Chiral or Achiral?



2-bromopropane

Enantiomers



A chiral compound and its mirror image are

called

enantiomers

.

Enantiomers



Asparagine:

_mirror

plane

C

C O HO

CH₂

H NH₂

C

O NH₂ C

C

O OH

CH₂ H H₂N

C

O H₂N

Absolute Configuration



R

and

S

• Assign priorities to the remaining groups based on atomic numbers.

• Clockwise (highest to lowest priority) R

• Counterclockwise S

=

H C

CH₃ OH

CH₂CH₃

C CH₃

HO1 CH2 ₂CH₃

3

Absolute Configuration



Assign priority:

• Atomic number of atom directly bonded.

• If the same atom is bonded, go to the next atom, etc.

• Groups containing multiple bonds are treated as though multiple atoms were attached:

C O = C

O

O

C

C N C

Absolute Configuration



Determine the absolute configuration of the

following compounds:

C H₃C

Br Cl H

C F

D CH3 H

C (CH₃)₂CHCH₂

CH₃CH₂CH₂CH₂ Cl H

C C

CH₃CH₂ C

Absolute Configuration



Determine the absolute configuration of the

following compounds:

C

CH₃

H

CH₃CH₂ CH CH CH₃O

OH CH₃

C

CH₃

H

CH₃CH₂ CH CH CH₃O

OCH₃ CH₃

C CH₂=CH

CH₃CH₂ CH3 H

C CH₂=CH

(CH₃)₂CH C

 Plane-polarized light is produced by passing

normal light through a polarizer.

Optical Activity

Optical Activity

 However, when plane-polarized light passes

Optical Activity

 Optical Activity – The ability of a compound to

rotate the plane of polarized light.

 A compound that rotates the plane of polarization is said to be optically active.

 Chiral compounds are optically active and

achiral compounds are optically inactive.