Download CHEM 107

Part 2
• Chapter 14- aldehyde and ketone
– Predicting reactions.
• Chapter 14- Stereoisomerism
•
•
•
•
structural isomers
stereoisomers
chiral / achiral
enantiamers
Frequency: BB
Structural isomers and
Stereoisomers
http://www.studyvilla.com/isomerism.aspx
Structural Isomers and
Stereoisomers
Structural isomers- same molecular formula, but different
structural formula.
CH3CH2CHO propanal C3H6O
CH3COCH3 propanone C3H6O
H
H
C
H
O
O
H
C
C
H
Same molecular formula
C
H
H
C
H
H
C
HH
different structural formula
H
Structural Isomers and
Stereoisomers
•Stereoisomers – the same structural formula, but different
arrangement of the atoms in space. two types:
–Geometrical isomers (already have seen with alkenes)
• Butene
H
H
C
H
H
C
H
C
H
H
C
CH3
C
H
CH3
C
CH3
C
H
CH3
C
H
H
H
trans-
cis-
–Optical isomers – have non-superimposable mirror images
Optical Isomers
Best example is your hands (A)
Hands are non-superimposable
The molecule in (A) has
carbon in the center
(black sphere) with four
different atoms (shapes)
around it.
(B) Shows how one
isomer fits a template
and the other does not fit
the same template.
http://www.google.com/imgres?q=optical+isomers main_body.asp
Optical Isomers
• Non-superimposable mirror images are called chiral.
• The hands and feet are chiral.
• The glass, bat and ball are all
Superimposable and are
Called achiral.
• Chiral molecules are also called
enantiomers.
• In order for a carbon atom
to be chiral it has to have
four different atoms or groups
http://www.creation-science-prophecy.com/amino
of atoms attached to it.
Gum Drop Isomers
• Pair up
• Get a bag of gum drops, 8 toothpicks.
Questions: For each of the following indicate whether the object or the carbon
with the * is chiral or achiral and why:
1)
3) Glycerol, which is used to sweeten and preserve
foods.
HO
2)
H
OH H
C
C*
C
H
H
H
OH
4) Monosodium glutamate (MSG), which is used as a
flavor enhancer in foods.
Na+ -O
O
H
H
NH2 O
C
C
C
C
H
H
H
*
C
OH
5) Ibuprofen, which is a nonsteroidal antiO
infammatory drug.
CH3
H
H
C
OH
C
C
C*
CH3
CH3 H
H
Enantiomers : Your Nose
Knows.
http://www.newworldencyclopedia.org/entry/Spearmint
http://www.bojensen.net/EssentialOilsEng/Essential
Oils05A/EssentialOils05A.htm
Caraway seeds
used in rye bread
Olfactory receptors in
the nose detect these
enantiomers as two
defferent odors.
Taste buds in the
tougue can also
detect the difference.
http://butane.chem.uiuc.edu/cyerkes/Chem104ACSP08/Lecture_Notes_104/lect21c.html
Enantiomers: Pain
Relief
http://www.naproxensodium.org/
active
http://www.drugs-expert.com/naproxen/
inactive
http://www.chem.moravian.edu
http://www.google.com/imgres?q=optical+isomers main_body.asp
Represent Compounds
with Chiral Carbons
• 3-D models:
COOH
eye
Lactic acid
HO
H
CH3
http://www.3dchem.com/molecules.asp?ID=415
• 3-D to 2-D
dash and wedge model
COOH
HO
C
H
CH3
Remove the chiral C
COOH
H
HO
CH3
Fischer Projection
Enantiomers
• 3-D:
COOH
HO
COOH
H
H
OH
CH3
• 2-D:
CH3
COOH
COOH
H
HO
CH3
OH
H
mirror
CH3
Acetals and
Hemiacetals
Hemiacetals
• are carbon atoms that contain a hydroxyl group –OH
and an alkoxy group –OR.
• are formed when an alcohol adds to an aldehyde or
ketone in the presence of an acid catalyst.
• react with a second alcohol molecule to produce an
acetal, a carbon with two alkoxy groups –OR.
Acetals from Aldehydes
Alcohol adds to the aldehyde carbonyl producing a
hemiacetal. When a second alcohol adds, it
forms an acetal.
Acetals from Ketones
Ketones
 are less reactive than aldehydes because the
carbonyl carbon is more positive in aldehydes.
 react with one alcohol molecule to form a hemiacetal,
and react with a second alcohol molecule to form an
acetal.
Cyclic Hemiacetals
In glucose, a cyclic hemiacetal between the C═O group
and the –OH group on carbon 5, forms a stable,
six-atom ring.
Cyclic Acetals
Cyclic acetals
• form when an alcohol adds to a cyclic hemiacetal.
• are very important in carbohydrate chemistry.
It is the type of linkage that bonds glucose molecules to other
glucose molecules in the formation of disaccharides and
polysaccharides.
Glucose + Glucose =
Maltose
Maltose
• is a disaccharide consisting of two glucose molecules
linked by an acetal bond (shown in red).
• is produced from the hydrolysis of starch from grains.
• has one glucose that retains the cyclic hemiacetal bond
(shown in green).
Maltose
Maltose, a disaccharide,
is produced from the
hydrolysis of the starches
in grains, such as barley.