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Conjugation
• Which of the following compounds is conjugated?
O O O OH
A B C D
Conjugation
• Which of the following compounds is not conjugated?
N
A B C D
• Slides 4 and 5 are part of the same question.
Butadiene
• 2 conformations possible, both overall planar
s-ciss-cis-1,3-butadiene
s-transs-trans-1,3-butadiene
C
C C
C
HH
H
HH
H C
C C
CH
H
H
H
H
H
Butadiene
• Which conformation appears to be more stable?
a. s-cis
b. s-trans
c. neither
Butadiene
• Would forms A, C, and D contribute significantly?
a. yes b. no
This would be one explanation for the low degree of delocalization in dienes.
A B C
D
• Slides 8 9 and 12 pertain to the questions on slides 10 and 11.
SpectroscopyUltraviolet-Visible (UV-Vis)
• Many organic compounds absorb light at wavelengths below 300 nm.
• e.g. ethylene, - * transition, E = 173
kcal/mole, = 165 nm
SpectroscopyUltraviolet-Visible (UV-Vis)
• As conjugation is extended, what is happening to the the HOMO-LUMO energy gap?
a. increases b. decreases c. nothing
SpectroscopyUltraviolet-Visible (UV-Vis)
• As conjugation is extended, what will happen to the wavelength of absorption increases?
a. increases b. decreases c. nothing
• (E = hc/)
165 217 251 304
Reactions of Conjugated Compounds Dienes: 1,2- vs. 1,4-Addition
• Which ion is more likely to form and why?
H BrC
HH
H
H
H
CH
H
H
+
vs.
A B
A
Reactions of Conjugated Compounds Dienes: 1,2- vs. 1,4-Addition
• The numbering in this case has nothing to do with nomenclature. Instead the numbering indicates where the “pieces” of the electrophile attached.
• Which alkene would be more stable, the 1,2 or 1,4
addition product?
a. 1,2 addition product b. 1,4 addition product
c. neither
Reactions of Conjugated Compounds Dienes: 1,2- vs. 1,4-Addition
• Which C would be expected to have more partial positive charge?
a. Y b. Z c. neither
(Y)
(Z)
Reactions of Conjugated Compounds Dienes: 1,2- vs. 1,4-Addition
• Which product will form faster?
a. 1,2 addition product
b. 1,4 addition product
c. neither
Diels-Alder Reaction
• Could another product have formed?
a. yes b. no
OO
+150º
O
Diels-Alder Reaction
• Diels-Alder reaction : addition of dienophile to diene is syn or anti? a. syn b. anti c. both d.neither
CO2CH3
H3CO2C
CO2CH3
CO2CH3
Diels-Alder Reaction
• Can the reaction occur in the s-trans conformation? a. yes b. no
+ ?
• How many isoprene units are present in nepetalactone?
O
O
CH3
CH3H
H
2
• Predict the major product of
the following reaction. Cl2low temperature
a. b. c. d. e.Cl
Cl
Cl
Cl
Cl Cl
Cl
Cl
What is the major product for the following reaction?
a. b. c. d. e.
R1
+
O
O
R2
R1O
O
H
H
R2
R1O
O R2
H
H
O
O
R1
R2
H
H
O
O
R1
R2
H
H
O
O
R1
R2
Which of the following is not a p molecular
orbital if 1,3-butadiene?
a. b. c.
d. e.
Which p molecular orbital reduces the p bonding character between C2 and C3 of 1,3-butadiene (and is still a bonding
MO)?
a. b. c.
d. e.
