This document provides an overview of proton NMR spectroscopy. It begins with definitions of light and the electromagnetic spectrum. It then discusses spectroscopy in general and introduces NMR, focusing on proton NMR. The key concepts of proton NMR covered include its principle, instrumentation, chemical shifts, spin-spin splitting, deuterium exchange, and the n+1 rule. Applications discussed include distinguishing isomers, determining molecular weight, and studying tautomeric mixtures. Clinical, agricultural, and biological applications are also mentioned.

1. PROTON NMR
SPECTROSCOPY
Presented By:
Bhushan. L. C.
Guided By:
Prof. Dr. J. S. Biradar
DEPARTMENT OF
POSTTGRADUATE AND RESEARCH
IN CHEMISTRY,GUK

2. Contents :
1) Light
2) Introduction to
Spectroscopy
3) Types of
Spectroscopy
4) Introdruction to
NMR
5) Proton NMR
6) Principle
7) Instrumentation
8) Chemical Shift
9)Internal Standard
10)Spin-Spin Splitting
11) Deuterium
Exchange
12) n+1 Rule
13) Applications

3. LIGHT
Light is electromagnetic radiation within a
certain portion of the electromagnetic spectrum.
The word usually refers to visible light, which is
visible to the human eye and is responsible for the
sense of sight. Visible light is usually defined as
having a wavelength in the range of 400
nanometres (nm), or 400×10−9 m, to 700
nanometres – between the infrared (with longer
wavelengths) and the ultraviolet (with shorter
wavelengths).Often, infrared and ultraviolet are
also called light.

4.  The term light sometimes refers to electromagnetic
radiation of any wavelength, whether visible or not. In this
sense, gamma rays, X-rays, microwaves and radio waves are
also light. Like all types of light, visible light is emitted and
absorbed in tiny "packets" called photons, and exhibits
properties of both waves and particles
Electromagnetic Spectrum & Visible Light
Generally, EM radiation, or EMR (the designation
'radiation' excludes static electric and magnetic and near
fields) is classified by wavelength into radio, microwave,
infrared, the visible region that we perceive as light,
ultraviolet, X-rays and gamma rays.

5. Introduction to Spectroscopy
Spectroscopy may be defined as the “Technique
whereby we measure the amount of radiation absorbed
by a substance at various wavelengths”.
Absorption of photons by the molecule may
change its internal energy (electronic, vibrational or
rotational energy) or may cause transition between
different spn orientations of nuclei in a magnetic field
From this useful information,to ascertain the
structure of an unknown organic compound whether
obtained by synthetic process or form a natural sources
is a fundamental operation in chemistry.

6. TYPES OF SPECTROSCOPY
The study of spectroscopy can be studied mainly two
types as followings,
1) Atomic Spectroscopy
2) Molecular Spectroscopy
TYPES OF MOLECULAR SPECTROSCOPY
1. Infrared Spectroscopy
2. Pure Rotation (Microwave ) Spectroscopy
3. Ultra violet & Visible Spectroscopy
4. Nuclear Quadruole Resonance (NQR) & Nuclear
magnetic resonance (NMR) Spectroscopy
5. Electron Spin Resonanace (ESR) Spectroscopy
6. Mass spectroscopy

7. INTRODUCTION TO NMR
 The study of absorption of radiofrequency radiation
by nuclei in a magnetic field is called Nuclear Magnetic
Resonance.
• Nuclear magnetic resonance spectroscopy is
basically another form of absorption spectrometry. It
involve change of the spin state of a nucleus, when the
nucleus absorb electromagnetic radiation in a strong
magnetic field.
• The source of energy in NMR is radio waves which have
long wavelengths, and thus low energy and frequency.
• When low-energy radio waves interact with a molecule,
they can change the nuclear spins of some elements having
spin state 1/2, including 1H and 13C.

8. 1H NMR
 The Nucleus of a hydrogen atom(proton) behaves as a
spinning bar magnet because it possesses both electric field
and magnetic spin. Like any other spinning charged body,
the nucleus of hydrogen atom generates a magnetic field.
 Nuclear Magnetic Resonance involves the interaction
between an oscillating magnetic field of electromagnetic
radiation and the magnetic energy of the hydrogen nucleus
or some other type of nuclei when these are placed in an
external static magnetic field.

9. Principle Of Proton NMR
• When a charged particle such as a proton spins on
its axis, it creates a magnetic field. Thus, the nucleus
can be considered to be a tiny bar magnet.
• Normally, these tiny bar magnets are randomly
oriented in space. However, in the presence of a
magnetic field B0, they are oriented with or against this
applied field. More nuclei are oriented with the applied
field because this arrangement is lower in energy.
•

10. All nuclei carry a charge. In same nuclei charge spins
on the nuclear axis and this circular, charge generates a
magnetic dipole along the axis. The angular momentum of
the spinning charge can be described in terms of quntum
number I, “ I = 0, ½, 1, 3/2 5/2…….. and so on. If spin I = 0
no spin and hence no 1H NMR phenomenon

11. Spin active nuclei have permanent magnetic moments and
quantized nuclear spin states. The number of spin states for a
given nucleus is given by the expression (2I +1) where I is the
overall nuclear spin.
In a magnetic field, there are now two energy states
for a proton: a lower energy state with the nucleus
aligned in the same direction as B0, and a higher energy
state in which the nucleus aligned against B0
Alignment with the field (Lower energy state or
parallel to the field I = +1/2)
Alignment against the field (Higher energy state or
antiparallel to the field. I = -1/2)

12. As shown in figure. Two energy levels one is lower
energy states i.e, aligned or parallel I = +1/2 whose
population is N other is higher energy state I = -1/2,
antiparallel whose population is N then N > N in
accordance with the boltzman distribution.

13. Therefore,
,
.
since
Where ,
h  Planck’s constant.
  Frequency of oscillator
B o  Applied external magnetic field strength.
  Gyromagnetic ratio ( being ratio between the nuclear
magnetic moment)

14. Intrumentations :
Continuous Wave (CW) Spectrometer :
In the CW Spectrometers the spectra can be recorded
either with field sweep or frequency sweep.. Keeping the
frequency constant, while the magnetic field is varied (swept)
is technically easier than holding the magnetic field constant
and varying the frequency.

15. Instrumentations :
Pulse Technique & Fourier Tranform NMR Spectroscopy
(FTNMR):
The modern Fourier Transform (FT) spectrometer
operates with pulse technique when an rf pulse of short
duration excites all the nuclei simultaneously and all the
signals are collected at the same time with a computer. The
individual method allows several hundred runs to be
collected within seconds. The data are mathematically
converted (a fourier transform ) to a spectrum.
Advantages of FTNMR:
 It is much faster and More sensitive.
 It can obtained with less than 5mg of compound.

16. Chemical Shift :
The difference in the absorption of position of a
particular proton from the absorption position of a reference
proton is called Chemical shift.
Chemical shifts position are normally expressed in
(delta) units, which are defined as proportional differences,
in parts per million(ppm), from an appropriate reference
standard (TMS in case of proton NMR).

17. Internal Standards
Reference materials which is commonly employed as
internal standard is the universally accepted reference is
Tetramethyl Silane (TMS).
Characterstic Features of TMS
Si
CH3
CH3
CH3
H3C
•It is chemically inert and miscible with a large range of solvent
•It is highly violatile and can be easily removed to get back the
sample
•TMS give only one peak
•TMS gives an intense sharp peak at low concentrations.
•It has a low boiling point 26.5 0C

18. Spin -Spin coupling or spin - spin splitting :
Splitting of the spectral lines arises because of coupling
interaction between neighbour protons and is related to
the number of possible spin orientation that these
neighbours can adapt. The phenomenon is called either
spin-spin spilitting or spin-spin coupling.
Nonequivalent protons on adjacent carbons have
magnetic fields that may align with or oppose the external
field.
This magnetic coupling causes the proton to absorb
slightly downfield when the external field is reinforced and
slightly upfield when the external field is opposed.

19. Nonequivalent protons on adjacent carbons
1,1,2-Tribromoethane
Triplet: 2 Adjacent ProtonsDoublet: 1 Adjacent Proton

20. Deuterium Exchange :
If deuterium oxide, D2O, is used as solvent for NMR work,
the D2O exchanges with labile protons such as OH, NH and
SH. In effect, because of the rapidity of the exchange, R-OH
becomes ROD, RCOOH becomes RCOOD, RCONH2
becomes RCOND2 Etc.
ROH + D--O--D ROD + H--O--D
This technique of detraction is widely used to detect the
presence of –OH, -NH & SH groups and is easily carried out,.
The NMR spectrum can be carried out.
The method can be extended to detect reactive
methylene groups, such as those flanked by carbonyl.

21. n+1 Rule :
 The number of peaks in a multiplet can give
additional information about the structure
 The splitting of peaks is caused by the
neighbouring carbon’s hydrogen atoms
 Protons in the same environment are said to be
equivalent and as such behave as one proton.
This follows the n + 1 rule.
 n is the number of hydrogen atoms attached to the
next-door carbon
 n + 1 is how many peaks will be seen in the cluster

22. Applications Of NMR :
1) Distinction between cis-trans isomers and conformers.
The cis and trans isomers of a compound can be easily
distinguished as the concerned protons have different
values of the chemical shift as well as coupling constants.
Ex: High resolution PMR spectroscopy has been used to
distinguish between cis and trans decline.

23. 2) Determination of the molecular weight :
Proton NMR spectroscopy has been used to determine the
molecular weight of an unknown compound by comparing
the intergrated instensities of an added standard and a
recongnisabel peak or group of peaks of the unknown in a
solution containing a known weight of a each substance.
3) Determination of the relative amounts of tautomers in a
tautomeric mixture:
Proton NMR spectroscopy has been used to
 Study the keto enol equilibrium β – diketones and β –
ketoesters
Ex: Acetyl acetone

24. Enol protons: keto protons = 8:2 or 4:1
Thus we say that 80% of enolic form and 20% of
ketonic form are present in the equilibrium mixture of
acetyl- acetone.
The nmr spectrum of pure acetylacetone shows signal
for the following kinds of equivalent protons.

25.  NMR has potential application in the fields of agriculture.
The distribution of water, oil the nature of binding of water,
the germination process can all be investigated. The 1H – MRI,
in a specific variety of green chilli, for example, clearly
demonstrantes there are different distribution of water, and oil
in a specific variety of ground nut seed has been investigated
4) Clinical and agricultural application:
 The MRI is able to defect motion of the blood flow because
the oxygenated and deoxygenated blood carry distinct NMR
signals.
 While most MRI and in-vivo studies have been performed
using PMR, phospours is another NMR abundance finds
numerous applications in metabolic and other physiological
studies.

26. General Applications of NMR Spectroscopy :
 NMR is used in biology to study the biofuids, cells, perfused
organs and bio macromolecules such as nucleic acids (DNA.
RNA) carbohydrates proteins and peptides, And also labeling
studies is biochemistry.
 NMR is used physics and physical chemistry to study high
pressure diffusion, Liquid crystals liquid crystal solutions,
menbranes, rigid solids.
 NMR is used in pharmaceutical science to study
pharmaceutical and drug metabolism.