10/09/2014
10
CALCULATING CONFORMATIONAL FREE ENERGY
USING COUPLING CONSTANTS
[1-X] [X]
Ha
Hb
H
X
O Ha
Hb
H
X
O
Average JH b = Jaa[X] + Jee[1-X]
Average JH a = Jae[X] + Jea[1-X]
The values of Jaa, Jee, Jae and Jea are determined from
Conformationaly rigid cyclohexanone systems
NMR OF 4-t-BUTYL-2-NITROCYCLOHEXANONE
Jaa = 12.6 Hz
Jae = 5.7 Hz
Jea = 5.2 Hz
Jee = 4.3 Hz
NMR OF 2-NITROCYCLOHEXANONE
Average JH Ha = 10.6
Average JH Hb = 7.6
CALCULATING THE CONFORMATIONAL FREE ENERGY OF 2NITROCYCLOHEXANONE
USING COUPLING CONSTANTS
NO2
NO2
O
H
Hb
HaOH
Hb
Ha
[1-X] [X]
Average JH b = Jaa[X] + Jee[1-X]
10.6 = 12.6 [X] + 4.3 [1-X]
X = 0.76
K = [X]/[1-X] = 0.76/0.24 = 3.17
G# = -RTlnK = -(2.3)(2)(298)log3.17 = 0.73kcal/mol