Spectroscopy-1hnmr

Electron Spin

Nuclear Magnetic
Resonance
(NMR)
Spectroscopy
Organic Chemistry BCH3015

• Electron spin is quantized.
• The spin quantum number ms has only two allowed values: ms = +½ or –½

• The two directions of spin create oppositely spin create oppositely directed magnetic fields. fields.
61

Proton Spin

Organic Chemistry BCH3015

62

Nuclear Spin States

• A proton (the nucleus of a 1H atom) also possesses spin.

For each nucleus having the spin quantum number I, there are (2I + 1) allowed spin states.

• The spin of a proton is also quantized.

mI   I , ( I  1), ..., ( I  1),  I
• The spin quantum number of a proton is:

I

1
2

Example: For the nucleus of
For the nucleus of

35
35Cl,

I

3
2

• There are two allowed spin states mI:
There are 4 allowed spin states: are allowed spin states:

1
1
 or 
2
2
Organic Chemistry BCH3015

63

311
3
 ,  ,  , or 
222
2

Organic Chemistry BCH3015

64

Some Common Nuclei

We
We Will Only Discuss
Proton Nuclear Magnetic Resonance

• Any atomic nucleus that has a odd mass number and/or odd atomic number has a quantized spin angular momentum.
El
Element

1
1

H

2
1

H

12
6

C

13
6

C

14
7

1H

NMR
1
I
2

N

Nuclear spin quantum spin quantum number 1
2

1

0

1
2

1

Number of spin states of spin states

2

3

0

2

3

17
8

19
9

31
15

Element

16
8

O

O

F

P

35
17

Cl

Nuclear spin quantum spin quantum number 0

5
2

1
2

1
2

3
2

Number of spin states of spin states

0

6

2

2

4

Organic Chemistry BCH3015

65

Nuclear Spin

Allowed
Allowed Spin States
1
1

and

2
2
Organic Chemistry BCH3015

66

Effects of an Applied Magnetic Field B0

• The spinning nucleus generates a magnetic field. spinning nucleus generates magnetic field

Ealigned < Eagainst
• B0 applies