Page 96 - Org 3 theoritical book 2024-25

Clinical Pharmacy PharmD - 2024/2025 Level 2 Pharmaceutical Organic Chemistry-3 (PC 305)
Coupling Constant (J

❖ J value = (line 1 chemical shift – line 2 chemical shift) x frequency of NMR machine.

Ex 1:

❖ In case of 400 MHz NMR Instrument,
✓ J of peak a = (7.44-7.42)x400 = 8 Hz
✓ J of peak b = (6.75-6.73)x400 = 8 Hz
✓ Coupled peaks will have the same J value, Ja,b= 8 Hz

Ex 2:

▪ Here Hb peak will have 2 values of J the big one is for ortho coupling and is
st
nd
calculated by = (mid point of 1 db – mid point of 2 db) X frequency of NMR.
(it should be same of J value of Ha)
▪ The small J value is for meta coupling and is calculated by = (line 1 – line 2) of
any of the 2 db peaks X frequency of NMR. (it should be same of J value of Hc).