Soluções para Espectroscopia Ultravioleta

Prévia do material em texto

Solutions for Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy
CH3O
CH3O
O
CH3
O OEt
O OMe
O OMe
CH3O NC
NC
CN
CN
H
CN
O
Ph
Ph
CN
O
O
O
++
(b)(a)
15
+
(c)
+
(d)
++
(f)(e)
(a) (b) (c)
16 Chiral products from achiral reactants produce racemic mixtures.
O
O
H3CO
H
H
H CH3
O
O
O
all cis
CH3
O
CH3
C
N
O
CH3
CH3O
CHO
COOCH3
CH3O
H
H
CH3
CH3
CN
(b)(a)
17 These structures show the alignment of diene and dienophile in the Diels-Alder transition state, 
leading to 1,4-orientation in (a) and 1,2-orientation in (b).
18 For clarity, the sigma bonds formed in the Diels-Alder reaction are shown in bold. Chiral products 
from achiral reactants produce racemic mixtures.
(b)(a)
(c)
This left structure is a VERY minor resonance contributor; 
however, it explains the orientation for the diene as carbon-1 
is more negative and carbon-2, a 3° carbon, is slightly more 
positive because of methyl group stabilization.
(d)
OCH3
O
346