See Poster
TH 7th floor
hallway!
Help Needed!
at ACS Family Science Night
at Oak Grove Middle School, Concord
Wednesday, Oct.22, 6 - 9 pm
What would you do?
• Help set up experiments
• Help middle school
students (and their
parents) do the
experiments
Please email
msequin@sfsu.edu if you
can help! It’s fun!
What would you get?
• experience in working
with youngsters and
showing them the fun of
science (chemistry!)
• a nice entry on your
resume
• a good impression with your
instructor!
Smells and
Molecules
Today:
• Diels-Alder (cont.)
H
H
O
+
diene
O
O
O
I
D.-A. adduct
O
dienophile
O
• Esterification (Exp.5) a first introduction
CO2 H
+ CH 3 OH
H
+
CO2 CH3 + H 2 O
Diels – Alder Reactions (Exp.4)
Diels-Alder reactions are another example of syntheses
that introduce additional C – C bonds to a reactant.
Which structural feature is always formed as the result of
Diels-Alder reactions?
A cyclohexene ring. A stereospecific reaction, s-cis addition
Diels-Alder reactions are what type of reactions?
Diels – Alder Reactions
The Diels-Alder reaction requires a 1,3-diene and a dienophile.
1,3-diene in s-cis conformation
Dienophile: alkene, most reactive if EWG is attached
Diels – Alder Reactions
The Diels-Alder reaction requires a
1,3-diene (in s-cis) and a dienophile (alkene, best with EWG attached).
Reaction equations for our experiment:
Retro Diels Alder: Cracking of dimer
H
H
room temp.
+
high temp.
I
Dimer
dicyclopenatdiene
Diels Alder: Reaction of 1,3-cyclopentadiene with maleic anhydride
H
H
O
+
O
O
diene
O
Compare:
Hydrolysis of Diels-Alder product
H
H
H
H2O
H
O
O
O
Cis endo
O
I
O
dienophile
D.-A. adduct
II
CO2H
CO2H
• Polarity of I
versus II
• Mp. of I versus II
Diels – Alder Reactions
Which of the following dienes would be most reactive? why?
1,3-cyclopentadiene, 1,3-butadiene
(see problems on Report Form)
Which of the following dienophiles would be more reactive?
Ethene or maleic anhydride
Diels – Alder Reactions
Synthesis of Natural Products
C
A
D
B
Steroids
CH3
C
CH3
A
CH3
D
CH3
B
HO
Cholesterol
Diels Alder
The H-NMR of the dimer of 1,3-cyclopentadiene is quite complex, with
many signals.
In contrast, the proton NMR of our Diels-Alder product is simple, with
few signals; the same is true for its hydrolysis product. How can you
explain this?
emp.
H
H
H
H
O
O
O
mp.
O
I
O
dicyclopenatdiene
dienophile
O
H
H
H2O
H
H
O
O
I
O
II
CO2H
CO2H
Methyl Benzoate Synthesis
CO2 H
+ CH 3 OH
H
+
CO2 CH3 + H 2 O
You will heat your reaction under reflux for 1 hour!
Do Practice Problems, calculations …
In order to increase the yield of the ester, which of the
following would help?
•
use an excess of methanol
•
use an excess of conc. sulfuric acid
Calculations …!
Why sulfuric
acid and not
HCl?
Esters and Esterifications
1. General properties of esters?
2. Compare the boiling points of carboxylic acids and
esters of similar molecular weight and explain.
3. Examples of esters in biological systems?
• Fats and Oils
• Waxes
• Ripening process in fruits
• phosphate esters in DNA
Salicin and Aspirin
OH
O
-D-glucose
O OH
C
O
O
Salicin
in willow bark
(Salix)
C
CH 3
Next time:
Conclusion of “Esterification” (Exp. 5)
Grignard reactions (Exp. 6)