Sistemas Conjugados e Espectroscopia UV

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Solutions for Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
27 continued
H H
O
HH2C
H2C H
O
HH
H2C C H
O
HH
C
H H
O
HH2C
(e)
most significant contributor—
negative charge on more electronegative atom
H2C
C
C
H
H
OCH3
C
OCH3
C
H
H
H2C H2C
C
C
H
H
OCH3
(h)
Most significant 
contributor—all atoms 
have full octets.
(g)
CH
O CH2
O
HC CH2
O CH2
O CH2
(f)
OO O O
H
CO O
Most significant 
contributor—all atoms 
have full octets.
A
λmax = 232 nm
Solved Problem 3
λmax = 232 nm
compare with dienes:
A = ε c l ε =
c l
l = 1 cm A = 0.74
convert mass to moles: 0.0010 g x 1 mole
255 g
= 3.9 x 10−6 moles
c = 3.9 x 10−6 moles
100 mL
1000 mL
1 L
= 3.9 x 10−5 Mx
ε = 0.74
( 3.9 x 10−5 ) ( 1 )
 ≈
28
(a)
19,000
(b) This large value of ε could only 
come from a conjugated system, 
eliminating the first structure. The 
absorption maximum at 235 nm is 
most likely a diene rather than a triene. 
 The most reasonable structure is: Table 2
350