This document provides an overview of NMR spectroscopy. It describes how certain nuclei can absorb electromagnetic radiation when placed in an external magnetic field due to their spin properties. When this occurs at the resonance frequency, the absorbed energy causes the nuclear spin states to flip. The document outlines the basic components of an NMR experiment, including the magnetic field, resonance process, and how the spectra is obtained. It also explains concepts like chemical shielding, use of a standard (TMS), and how chemical shifts are reported in parts per million based on the differences in resonance frequencies.

1. NMR Spectroscopy
Presented by:
Md. Masum Reza
Maria Akter

2. Contents:
 Introduction
 Magnetic properties of nuclei
 External magnetic field
 Effect of magnetic field
 spin states for nuclei
 Resonance Process
 Schematic diagram of NMR
 Shielding
 TETRAMETHYLSILANE – TMS
 Chemical shift

3. Introduction:-
 Nuclear Magnetic Resonance(NMR) is a spectroscopy
Technique which is based on the absorption of electromagnetic radiation
In the radio frequency region 4 to 9000 MHz by nuclei of the
atoms.
 Proton Nuclear Magnetic resonance spectroscopy is on of the
most powerful tools for determining the number of hydrogen or proton
In the compound.
 It determines the physical and chemical properties
of atoms or the molecules in which they are contained.

4. Magnetic properties of nuclei:
 All nuclei carry a positive charge, but only some have a charge spin on the
Nuclear axis which causes a magnetic dipole along the axis, therefore, posses an
Angular momentum.
 A spinning charge creates a magnetic moment, so these nuclei can be brought
Of as tiny magnets.
=>

5. External magnetic field:
When the external magnetic field is applied, nuclear magnetic can orient
themselves in 2I+1 spin states (equal to the number of magnetic quantum
number, m)

6. The relationship of nuclei and magnetic properties:
Only nuclei with spin number I≠0 can absorb/emit electromagnetic radiation.
nuclei example Spin quantum
No. (I)
Magnetic
Quantum no.
(m)
Allowed spin
states
Activity in
NMR
Atomic
mas
Atomic
no
odd odd or
even
1H, 13C, 19F,
31P
1/2 +1/2,-1/2 2(1/2)+1=2 NMR
active
odd odd or
even
35C 3/2 +3/2,1/2,-1/2,-
3/2
2(3/2)+1=4 NMR
active
even odd 2H, 14N 1 +1,0,-1 2(1)+1=3 NMR
active
even even 12C, 16O, 32S 0 0 2(0)+1=1 NMR
inactive

7. Effect of magnetic field:
No external
Magnetic field
External magnetic
Field(B0) is applied
The magnetic moments
Of protons are randomly
oriented
The protons orient themselves some
(spin +1/2) are parallel and some (-1/2) are
antiparallel to the applied magnetic field B0.

8. The energy difference between the allowed nuclear spin states for nuclei:
Depends on the strength of the external magnetic field, B0 according to the
equation:
Δ𝐸 =
γℎB0
2π
= γℎB0
Ƴ = gyromagnetic ratio
h = Plank’s constant
h = b/2π
NO
Spliting
At zero
external
field

9. Resonance Process:
Just as a spinning mass will precess in a gravitational field (a gyroscope),
the magnetic moment μ associated with a spinning spherical charge will
precess in an external magnetic field.
The frequency of precession is proportional to the strength of the magnetic
field, as noted by the equation: ωo = γBo . The frequency ωo is called the Larmor
frequency.
A Spinning Gyroscope
in a Gravity Field
A Spinning Charge
in a Magnetic Field

10. If rf energy having a frequency matching the Larmor frequency is introduced at a
right angle to the external field (e.g. along the x-axis), the precessing nucleus will
absorb energy and the magnetic moment will flip to its I = _1/2 state.
This excitation is shown in the following diagram.

11. Schematic diagram of NMR set-up:

12. Shielding:
An external magnetic field affects the motion
of the electrons in a molecule, inducing a
magnetic field within the molecule.
C H
H 0
The direction of the induced
magnetic field is opposite to
that of the applied field.
The induced field shields the nuclei (in this case, 13C and 1H) from the applied field.
A stronger external field is needed in order for energy difference between spin states to
match energy of rf radiation.

13. Downfield
Decreased shielding
Upfield
Increased shielding
1.09.0 8.0 7.0 02.03.04.05.06.010.0
(CH3)4Si (TMS)
H0
Chemical shift (d, ppm)
measured relative to TMS

14. TETRAMETHYLSILANE – TMS:
• non-toxic liquid - SAFE TO USE
• inert - DOESN’T REACT WITH COMPOUND BEING ANALYSED
• has a low boiling point - CAN BE DISTILLED OFF AND USED AGAIN
• all the hydrogen atoms are chemically equivalent - PRODUCES A SINGLE PEAK
• twelve hydrogens so it produces an intense peak - DON’T NEED TO USE MUCH
• signal is outside the range shown by most protons - WON’T OBSCURE MAIN SIGNALS
• given the chemical shift of d = 0
• the position of all other signals is measured relative to TMS
The molecule contains four
methyl groups attached to a
silicon atom in a tetrahedral
arrangement. All the hydrogen
atoms are chemically equivalent

15. Chemical shift:
Chemical shift is a measure of the degree to which a nucleus in a molecule is shielded.
• each proton type is said to be chemically shifted relative to a standard (usually TMS)
• the chemical shift is the difference between the field strength at which it absorbs
and
the field strength at which TMS protons absorb
• the delta (d) scale is widely used as a means of reporting chemical shifts
Observed chemical shift (Hz) x 106
d = ppm (parts per million)
Spectrometer frequency (Hz)
• the chemical shift of a proton is constant under the same conditions (solvent,
temperature)
• the TMS peak is assigned a value of ZERO (d = 0.00)
• all peaks of a sample under study are related to it and reported in parts per million
• H’s near to an electronegative species are shifted “downfield” to higher d values

16. -COOH
- C - X
H
- C - H
ROH
-C=CH-
-CHO
DOWNFIELD - deshielding
13 12 11 10 9 8 7 6 5 4 3 2 1 0 d
Approximate
chemical shifts
The actual values depend
on the environment

17. THANK YOU