286
286
Estimation of 19 F Chemical Shifts of Substituted Pyridines, Pyrimidines,
Pyrazines, and Triazines (δ in ppm) [5]
To estimate the 19 F chemical shifts of substituted 6-ring heteroaromatics, the same
increments, Z i , can be used as for substituted fluorobenzenes (see preceding page).
However, different base values, Y (as given below), apply depending on the number
and position of nitrogens and the position of the fluorine substituent in question:
Y:
-47.8
δ F = Y + ∑ Z i
N
F
N
F
N
F
N
N
F
N
N
F
N
N
F
N
N
F
N
N
F
N
N
F
N
N
N
F
-3.0
-18.3
-45.7
-3.5
Y:
-67.7
-52.1
-18.7
-41.8
-74.6
F
F
F
F
F
F
CF 3
F
F
F
CF 3
F
F
-163
-64
-55
-141
-160
-147
Heteronuclear NMR Spectroscopy
6