Page 87 - Pharmaceutical Organic Chemmistry-3 (Theoritical book) 24-25

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

❖ Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical chemistry technique

used in quality control and research for determining the content and purity of a sample

as well as its molecular structure.

❖ The principle behind NMR is that any movable electric charge will generate a

magnetic field and chemical atoms or nuclei have a charge; upon spinning generate a
magnetic field around itself.

❖ But not all chemical nuclei have spinning

property (could spin) and its magnetic

field could be recorded via NMR

Spectroscopy, only atoms having odd
mass number (that have two (or 4 in

limited cases)) spin states only are NMR-

magnetically active.

❖ The magnetic field generated by magnetically active atoms is weak to be sensed, in order

o
to be measured; it should be amplified by applying external magnetic field (H ).

Mass No. Atom 1 H 13 C 15 N 19 F 31 P
Natural Abundance > 99.98% 1.1% 0.364% 100% 100%
Average Time required by 400 MHz 2 mins 2 hrs 5 hrs 2 mins 2 mins
NMR spectrometer to record them

❖ The longer time required for recording magnetic field of C & N is due to their very
15
13
12
low natural abundance, as the normal most abundant isotope of carbon atom is C, and the
14
normal most abundant isotope of nitrogen atom is N.
2
16
14
12
➢ Note that: C, N, H & O could not be recorded by NMR as their mass No. is even
number.
❖ When matching occurred between the applied magnetic
field and the nuclear magnetic field of a certain atom, the
atom spinning direction is flipped then energy release
occurred. (this process is called nuclear magnetic

resonance)