Level 3 – Case 37
246
O
F
O 2 N
O
F
O 2 N
H H
O
F
O 2 N
H H
O
F
O 2 N
O
O 2 N
H H
O
O 2 N
F
(B)
O
O 2 N
O
O 2 N
F
(A)
(C)
1
E1
base
1
E2
base
2
2
E1cB
1
base
2
slow
3
4
4
3
3
4
4
3
3
4
step 1
step 2
Scheme 37.2
COCH 3
Ar D
D
*F
E1 transition state
G
secondary D KIE
F KIE
G 3
4
Figure 37.2
To distinguish between the two remaining alternatives is a bit more difficult. E2
and E1cB mechanisms have similar kinetic characteristics. They are bimolecular
processes and, in principle, all will be affected in the same way by an increase in
the base strength (the experimental data indicate that the elimination rate increases
with the pK a
K K of the base employed). As the data of primary and secondary D KIEs
provide information on the transition state of a reaction, a study of the different
transition states could help us to better distinguish among the different options.
246
O
F
O 2 N
O
F
O 2 N
H H
O
F
O 2 N
H H
O
F
O 2 N
O
O 2 N
H H
O
O 2 N
F
(B)
O
O 2 N
O
O 2 N
F
(A)
(C)
1
E1
base
1
E2
base
2
2
E1cB
1
base
2
slow
3
4
4
3
3
4
4
3
3
4
step 1
step 2
Scheme 37.2
COCH 3
Ar D
D
*F
E1 transition state
G
secondary D KIE
F KIE
G 3
4
Figure 37.2
To distinguish between the two remaining alternatives is a bit more difficult. E2
and E1cB mechanisms have similar kinetic characteristics. They are bimolecular
processes and, in principle, all will be affected in the same way by an increase in
the base strength (the experimental data indicate that the elimination rate increases
with the pK a
K K of the base employed). As the data of primary and secondary D KIEs
provide information on the transition state of a reaction, a study of the different
transition states could help us to better distinguish among the different options.