chem 312 notesStereochemistry conformational and reaction mechanism

Stereochemistry conformational and reaction mechanism

1. Stereoisomers
1

2. Stereoisomers
2
enantiomers
Stereoisomers that are
nonidentical mirror
images are called
enantiomers.

3. Visualize, visualize ….
3CC
Br
F
H
Cl
Br
H
CC
Br
F
H
Cl
Br
H
CC
H
Br
F
Cl
Br
H

4. Visualize, visualize …CC
Br
F
H
Cl
Br
H
CC
Br
F
H
Cl
Br
H
Cl
HBr
F
H Br
Cl
BrH
F
Br H
4

5. Visualize, visualize …
5
C
CH
3
Br
F
H
C
CH
3
F
Br
H
enantiomer
1..3..5…etc interchanges = enantiomer
2..4..6...etc interchanges = original compound
ODD:
EVEN:

6. Are these identical or are they
enantiomers?
6
C C
CH
3
Br
F
H CH
3
H
F
Br
C C
C
C
CH
3
Br
F
H CH
3
Br
F
H
CH
3
H
Br
F
H
CH
3
Br
F
ENANTIOMER ENANTIOMERSAME
1
2
3
YOU CAN USE
INTERCHANGES

7. Isomers
•Isomers:different compounds with the same
molecular formula
•Constitutional isomers:isomers with a
different connectivity
•Stereoisomers:isomers with the same
molecular formula, the same connectivity but
a different orientation of their atoms in space
that cannot be interconverted by rotation
about a single bond
7

8. Chirality
•Mirror image:the reflection of an object in a mirror
•Objects that are not superposable on their mirror
images are said to be chiral, that is, they show
handedness
•Objects that are superimposable on their mirror
images are said to be achiral, that is, they do not
show handedness. An achiral object has at least
one element of symmetry
8

9. Chirality
•A molecule cannot
be chiral if it has a
plane of symmetry.
9

10. Chirality
•A plane of symmetry is a plane that cuts
through an object in such a way that one
half of the object is an exact mirror image
of the other half.
•A molecule that has a plane of symmetry
must be identical to its mirror image and
therefore must be nonchiral, or achiral.
10

11. Elements of Symmetry
•Plane of symmetry: an imaginary plane
passing through an object dividing it such
that one half is the mirror image of the
other half
11Cl
ClBr
F F
Br
Cl Cl

12. Elements of Symmetry
•Center of symmetry:a point so situated that
identical components of the object are
located equidistant on opposite sides and
equidistant from the point along any axis
passing through the point
12Cl
Cl
Br
H
H
Br
center of
symmetry

13. Achiral
13
Two identical groups renders a
tetrahedral carbon achiral.F
Br
Cl
Cl
Cl
Cl
Br
F
The plane of the paper
is a plane of symmetry

14. Two Views of the Plane of
Symmetry
14
Cl
Cl
Br
F
F
Br
Cl Cl
plane of
symmetry
side view edge view

15. Symmetry Plane
15C
COOH
HH
COOH
C
CH3
H
COOH
OH
Symmetry plane No symmetry plane
achiral chiral

16. 16
CONSTITUTIONAL
ISOMERS
Isomers with a different
order of attachment of
the atoms in their
molecules
STEREOISOMERS
Isomers with the same order
of attachment, but a different
configuration (3D arrangement)
of groups on one or more of
the atoms
ISOMERS
Different compounds
with the same
molecular formula
cis/trans
ISOMERS
ENANTIOMERS
Stereoisomers whose
molecules are non-
superimposible mirror
images of each other
DIASTEREOMERS
Stereoisomers whose
molecules are not mirror
images of each other
each isomer could
double bond or ring
both can apply
have stereoisomers
with a ring
TYPES OF ISOMERISM(geometric)

17. Stereogenic Carbons
17Br
F
H
Cl
stereocenter
This is one type of ….
…. others are possible
A stereogenic carbon is tetrahedral and
has four different groups attached.

18. •Tetrahedral carbons with 4 different
attached groups are chiral.
•Its mirror image will be a different
compound (enantiomer).
=>
18

19. Enantiomers
•Enantiomers:stereoisomers that are
nonsuperposable mirror images; refers to
the relationship between pairs of objects
19

20. Enantiomers
20Br
F
H
Cl Cl
H
Br
F H
F
Br
Cl
rotate
this molecule
is chiral
note that the fluorine
and bromine have been
interchanged in the
enantiomer
do interchanges in class

21. Enantiomers
21
•Lactic acidC
C
HO
CH
3
H
OHO
C
C
OH
H
3
C
H
O OH

22. Enantiomers
•1,2-propanediol
22CH
3
CHCH
2
OH
OH C
OH
H
CH
2
OHH
3
C C
OH
H
HOH
2
C CH
3

23. Enantiomers
•3-Chlorocyclohexene
23Cl
H
Cl
H Cl