1

Chapter 8

Mechanism Experiments

2

σ ValuesSubstituent σmeta σpara σ+ σ–

-NH2 -0.09 -0.30 -1.3 -0.30

-OH 0.13 -0.38 -0.92 -0.22

-OCH3 0.10 -0.12 -0.78 -0.12

-C(CH3)3 -0.09 -0.15 -0.26 -0.26

-CH3 -0.06 -0.14 -0.31 -0.31

-Si(CH3)3 -0.04 -0.17 -0.07 0.08

H 0 0 0 0

-Ph 0.05 0.05 -0.18 0.08

-I 0.35 0.18 0.13 0.28

-Br 0.37 0.26 0.15 0.26

-Cl 0.37 0.24 0.11 0.24

-F 0.34 0.15 -0.07 0.15

-C(O)CH3 0.36 0.47 0.47 0.82

-CF3 0.46 0.53 0.53 0.74

-CN 0.62 0.70 0.70 0.99

-NO2 0.71 0.81 0.81 1.23

-N(CH3)3+ 0.99 0.96 0.96 0.96

3

ρ

4

ρ

X ρ

I +2.07

Br +2.14

OTs +2.27

Cl +2.61

S(CH3)2 +2.75

F +3.12

N(CH3)3 +3.77

Y

X NaOEt

Y

+ NaOEt + NaX

5

σ+ vs. σ–

Br2

Br HBr–

Br

+ HBr

Brown, H. C.; Okamoto, Y. J. Am. Chem. Soc., 1958, 80, 4979

6

Exothermic Reaction

7

Endothermic Reaction

8

Thermoneutral