Page 94 - Org 3 theoritical book 2024-25

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

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1
❖ Coupling with another nuclei than H (with F mainly):

1
19
• F act as H and splits the neighboring
1 H into doublet.

❖ Splitting into doublet of doublet (dd) instead of triplet (t):

• This occurs when a H couples
1

with two magnetically non-
1
equivalent H atoms.
• Ex:
1,2,4 substituted benzene rings
& other similar special cases

❖ Coupling with exchangeable Hs (OH, COOH, NH2, SH):
• These 3 Hs in CH3 of methanol should
couple with H on OH to produce a

quartet of OH and a doublet of CH3
but due to:
1.  Spinning of H on OH.

2. Its ability to exchange with
impurities they appear as two
singlets.
• ↓ Temperature & using highly pure
& very well dried sample will help to

see this splitting.

Coupling Constant (J

❖ Coupling Constant (J): It is the

distance in Hz between the lines in

doublets & other splitted peaks.
❖ It is a physical constant depending on

1
the chemical nature of H and not on
the frequency of the NMR instrument.