introduction, principle, quantum number, instrumentation, application of NMR Spectroscopy

1. :-RITESH PRATAP OJHA*
M PHARM (1ST YEAR)
*R A M - E E S H I N S T I T U T E O F V O C AT I O N A L A N D T E C H N I C A L
E D U C AT I O N
NMR Spectroscopy

2. Index
 Introduction
 History
 Quantum number & their role
 Principle
 Instrumentation
 Solvent used
 Chemical shift & factor affecting it
 Ft-NMR & 13-C NMR
 Application

3. Introduction
 NMR Spectroscopy is abbreviated as Nuclear Magnetic Resonance
spectroscopy, which means spectroscopy on the basis of resonance of
nucleus that happens because of magnetic field applied over it.
 It defines as it is the study of molecules by recording the interaction of
radiofrequency (Rf) electromagnetic radiations with the nuclei of
molecules placed in a strong magnetic field.

4. History
 NMR was first detected experimentally at the end of 1945, nearly concurrently
with the work groups Felix Bloch, Stanford University and Edward Purcell,
Harvard University.
 The first NMR spectrum was first published in the same issue of the Physical
Review in January 1946. Bloch and Purcell were jointly awarded the 1952
Nobel Prize in Physics for their research of Nuclear Magnetic Resonance
Spectroscopy.
 The research in the organic lab has been significantly improved with the aid of
the NMR. Not only can it provide information on the structure of the molecule,
it can also determine the content and purity of the sample.
 Proton (1H) NMR is one of the most widely used NMR methods by organic
chemists. The protons present in the molecule will behave differently
depending on the surrounding chemical environment, making it possible to
elucidate their structure.

5. Quantum number & its role
 The set of numbers used to describe the
position and energy of the electron in an
atom are called quantum numbers. There
are four quantum numbers, namely,
principal, azimuthal, magnetic and spin
quantum numbers.
 NMR is a bridge to the microscopic
quantum world of nuclear spins. Everything
rotates or spins, and for those who don't, we
give them spin (number) = 0. The nucleus is
composed of protons and neutrons, each
carrying an internal spin (spin = 1/2) Angular momentum of
Spinning charge (I)

6. Principle of NMR
 The basic principle behind NMR is that some
nuclei exist in specific nuclear spin states
when exposed to an external magnetic field.
NMR observes transitions between these spin
states that are specific to the particular nuclei
in question, as well as that nuclei's chemical
environment.
 Nuclei with an odd mass or odd atomic
number have "nuclear spin" (in a similar
fashion to the spin of electrons). Since a
nucleus is a charged particle in motion, it will
develop a magnetic field.
 To be NMR-active, a nucleus must have a
non-zero nuclear spin (I ≠ 0).

7. Instrumentation
This instrument consists of nine major parts, They are discussed below:
 Sample holder – It is a glass tube which is 8.5 cm long and 0.3 cm in
diameter.
 Magnetic coils – Magnetic coil generates magnetic field whenever current
flows through it
 Permanent magnet – It helps in providing a homogenous magnetic field at
60 – 100 MHZ
 Sweep generator – Modifies the strength of the magnetic field which is
already applied.
 Radiofrequency transmitter – It produces a powerful but short pulse of
the radio waves.
 Radiofrequency – It helps in detecting receiver radio frequencies.
 RF detector – It helps in determining unabsorbed radio frequencies.
 Recorder – It records the NMR signals which are received by the RF detector.
 Readout system – A computer that records the data.

8. Sample holder

9. Solvent requirement in NMR
 Solvent that are used in NMR should not contain Hydrogen atom.
 It is magnetically isotropic in nature means all directions they are
equally magnetic field.
 Solvent are also following characteristics:
a) chemically inactive, b) volatile in nature,
c) solvent able to dissolve the sample approximately 10%.
 These are some examples of commonly used solvents in NMR:
1. Carbon tetrachloride (CCL4),
2. Deuterated water(D20),
3. Deuterated methanol(CD3OD) etc.

10. Chemical shift
 Chemical shift is the difference between the absorption position of a sample
proton and the absorption position of the reference compound.
 Factor affecting chemical shift
1. Inductive effect :- when proton is attached with any electro negative group.
Then proton will be deshielding and chemical shift will be increased.
2. Steric effect :– due to presence of bulk group will repell the e¯ could of
proton due to electrostatic repusion.
Increase deshielding so increase chemical shift value.
1. Hydrogen bonding :- Hydrogen atom goes for hydrogen bonding with two
electronegative atom
They will take the e¯ cloud from H and it will be deshielded.
Due to deshielding chemical shift value will be higher.
1. Hybridization :- Sp2 1:2 = Mild 𝛿−, Sp 1:1 =High𝛿−, Sp3 1:3= Low𝛿

11. Application
 An NMR spectrum gives the following information:
 a) The number of peaks indicate different types of
nucleus.
 b) The location of the peak indicates the type of
nucleus and chemical environment.
 c) The relative areas of the peaks gives the relative
number of each type of nucleus.
 d) Disruption in the peak, indicates that affected
nucleuses from each other