Sistemas Conjugados e Espectroscopia UV

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Solutions for Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
CH3
Br
Mg
CH3
MgBr
H2C
H2C
O
H3O+
C
H
C
H
CH3
CH3C OH
CH3
A
CH2
CH2
36 continued
π1
π2
π3
π4∗
π5∗(g) Again, it is π3 that determines the character of this species. When the single 
electron in π3 of the neutral radical is removed, positive charge appears only in 
the position(s) which that electron occupied. That is, the positive charge 
depends on the now empty π3, with empty lobes (positive charge) on carbons 1, 
3, and 5, consistent with the resonance description.
Again, it is π3 that determines the character of this species. The negative 
charge depends on the filled π3, with lobes (negative charge) on carbons 1, 3, 
and 5, consistent with the resonance description.
(h) π5∗
π4∗
π3
π2
π1
37
(a)
ether
(b) Use text Section 13D to predict λmax values. Alkyl substituents are circled.
desired product—not 
consistent with UV data
cisoid cyclic diene = 256 nm
1 extra alkyl group = 5 nm
TOTAL = 261 nm
transoid cyclic diene with one 
exocyclic double bond = 232 nm
2 extra alkyl groups = 10 nm
TOTAL = 242 nm
cisoid cyclic diene = 256 nm
2 extra alkyl groups = 10 nm
TOTAL = 266 nm—AHA!—
closest to observed value
actual product B
both
trisubstituted
C=C
disubstituted
trisubstituted
356