Close

Education

Education

Education

Education

Education

Education

## Description

NUGIE ARIMI AGNEMG RESONANCE
SPIE@IROSCOPY

RESENTED BY
Ss CMUNUIN

SAL CHEMISTRY
WBa Pat e

www.DuloMix.com

CONTENTS

e Introduction
e Fundamental principles of NMR
e Interpretation

¥ Chemical shift
Y Number of signals
¥ Spin-Spin coupling: Splitting of signals
Y Coupling constant
V Integrals

wwww..DDuulloMiix.ccoomm

NMR Spectroscopy

e Nuclear Magnetic Resonance is_ a branch of

spectroscopy in which radio frequency waves induce

transitions between magnetic energy levels of nuclei

of a molecule.

wwww..DDuulloMiix.ccoomm

_ Highest energy Lowest energy
Wavelength (nm) a Longer Wavelength

10°? 10° 10° 104 10° 108 19! 10!
| | | | | | | | | | | | | | |
T } T I
I I | |

Gamma | | Ulira- |= Io | ;
ray X-ray violet |’z Infrared Microwave ! Radio frequency

| } > | |
1 i l l

1 | | | | | | | | | | | |
10° 19!8 1o!° 10!4 10! 10! 108 10° 107

High Frequency —€— Frequency (s“’)

400 500 600 700 750 nm

Visible region

The Electromagnetic Spectrum
www.DuloMix.com

The frequency of radio waves lies between 107 and 10®cps

calculated by using the equation :

E=hy

h = Planck’s constant = 6.6 x 1027 erg sec

v = frequency = 107- 10° cps(cycles per sec).

wwww..DDuulloMiix.ccoomm

E = 6.6 x 10-77 x 107 ( or 10° ergs)
= 6.6 x 10-° ( or 6.6 x 10-9 ergs )

Energy of rf radiation is very small to vibrate, rotate , or

excite an atom or molecule. But this energy is

sufficient to affect the nuclear spin of the atoms of a

molecule.

wwwww.D.DuluoloMMixix..ccoomm 6

~ NUCLEAR SPIN

The nuclei of some atoms have a property called “SPIN”.

(a These nuclei behave as if

they were spinning.

See
This is like the spin property
of an electron, which can have

two spins: +1/2 and -1/2.
Each spin-active nucleus has a number of spins defined by
its spin quantum number, I.
The number of Spin states = 21 +1

wwww..DDuulloMiix.ccoomm

e If the number of neutrons and the number of protons are

both even, then the nucleus has NO spin. »C, «O ,32S etc.

e If the number of neutrons plus the number of protons is

odd, then the nucleus has a half-integer spin (i.e. 1/2, 3/2,

5/2) 1H,19F, 3:P

e If the number of neutrons and the number of protons are

both odd, then the nucleus has an integer spin (i.e. 1, 2, 3)

2H, yN

wwww..DDuulloMiix.ccoomm

Element H 2H 13 14 15 16 197 31p 32g

Nuclear spin
quantum Le ee ee eS eA ee
number ( J )

Number of Z 3 1 2 3 Z 1 2 DN
spin states

wwwww.D.DuluoloMMixix..ccoomm 9

Principle

e NMR spectroscopy is the interaction of magnetic field with spin

of nuclei and then absorption of radio frequency. For example,

the nucleus of proton ,H* has two spin rotations : clockwise

rotation with a spin quantum number I = +% and |

counterclockwise rotation with a spin quantum number I = – 4

e The number of spin sates is 2]+1 which is 2x (1/2) +1 = 2 state

wwwww.D.DuluoloMMixix..ccoomm 10

The two states
iv are equivalent

in energy in the
+1/2 -1/2 absence of a

magnetic or an

wwwww.D.DuluoloMMixix..ccoomm electric field.

e Without the magnetic field the spin states of nuclei

possess the same energy, and energy level transition is

not possible.

e When a magnetic field is applied, the separate levels

between these energy levels.

wwwww.D.DuluoloMMixix..ccoomm 12

Energy Differences Between Nuclear Spin S

oO

28 |
OY
= increasing field strength ASSEN

no difference in absence of magnetic field
proportional to strength of external magnetic field

www.wD.uDluolMoiMxi.xc.coomm 13

= Some important relationships in NMR

Units

The frequency of absorbed
Hz

is proportional to

the energy difference between kJ/mol

two nuclear spin states (kcal/mol)

which is proportional to

the applied magnetic field tesla (T)

wwwww.D.DuluoloMMixix..ccoomm

Magnetic properties of nuclel

° 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.

wwww..DDuulloMiix.ccoomm

® But when magnetic field is applied, the proton (H)

posses spin & their own magnetic field align

themselves either or opposite to magnetic field.

° For e.g. 1H has +1/2 & -1/2 spin state, the proton (H)

have +1/2 spin state align themselves with field

(Lower energy) and with -1/2 spin state align

opposite to field (Higher energy).

wwww..DDuulloMiix.ccoomm

A spinning proton re

crea tmagenestic field.

o

The nuclear | are

oriwieth nor tagaeinsdt B ..

www.Dulo Mix.com

Nuclear Spin
Copyright © The McGraw-Hill Companies, inc. Permission required for reproduction or display

O s

Ho

(a) No external magnetic field (b) Apply external magnetic field #¢

www.wD.uDluolMoiMxi.xc.coomm 18

Higher

energy state Spin —4
(aligned against
the applied field)

Lower

energy state Spin +4

(aligned with
the applied field)

Change in spin state energy separation with increase by applied
magnetic field ,B,

wwwww.D.Dul uoloMMixix..ccoom m 19

External Magnetic Field
When placed in an external field, spinning

protons act like bar magnets.

GG
lower energy higher energy
more stable less stable

www.wD.uDluolMo iMxi.xc.coomm 20

THE “RESONANCE PHENOMENON

absorption of energy by the
spinning nucleus

wwwww..DDuullo Miix.ccoomm

N

> -1/2
unal igned In a strong magnetic

field (B,) the two
spin states differ in

energy.

+1/2

aligned
B

O
wwwww.D.DuluoloM Mixix..ccoomm 22

Two Energy States

The magnetic fields of wo

(| B state —

the spinning nuclei ‘ bit p Es

Y
will align either with
the external field, or Bo hv = AE

against the field.
A

A photon with the right
( | ) & state—

amount of energy can : Le

be absorbed and
cause the spinning
proton to flip.

wwwww.D.DuluoloMMixix..ccoomm

Excited state = High energy

N S

7) s 7

Energy Released

Aligned = Low Energy Back to low energy ground state

wwwww.D.DuluoloMMixix..ccoomm

e According to the quantum theory, a spinning nucleus

can only have values for the spin angular momentum

given by the equation :

Spin angular momentum = [I(I+1)]2/2 h / 2u

| = Spin quantum number

h= Plancks constant

wwww..DDuulloMiix.ccoomm

® But U=y~x spin angular momentum

LL = magnetic moment of the nucleus

y = gyro magnetic ratio

e If a nucleus having a magnetic moment is introduced into a

magnetic field , Hy the two energy levels become separate

corresponding to m , = -1/2 (anti-parallel to the direction of

magnetic field) and m, = +1/2 (parallel to the direction of

magnetic field).

wwwww.D.DuluoloMMixix..ccoomm 26

e Fora nucleus with I = 1/2, the energies E, and E, for the
two states with m , = +1/2 and m , = -1/2, respectively,
are
B= r/o |v hy |

E,=+1/2|yh2/p] H,

wwww..DDuulloMiix.ccoomm

——
T=1/2,m=+1/2,-1/2

Energy

No field

m=- 1/2

a

a a

m=+1/2 ‘
“§

BS
m=+1/2

www.Dulo Mix.com

° When the nucleus absorbs energy, the nucleus will be

promoted from the lower energy state E,, to the

higher energy state E, by absorption of energy , AE,

equal to the energy difference, E, —E, .

e It means that the absorption of energy AE changes

the magnetic moment from the parallel state m , =

+1/2 to the anti-parallel state (m , = -1/2).

wwww..DDuulloMiix.ccoomm