Spin-spin coupling in NMR spectroscopy
Spin - spin coupling :-
The NMR spectrum represent total chemical equelent proton present in the molecule
It is observed that proton, not observed a signal line the signal appear at multiplate splitting of in observed the region of splitting is spin -spin coupling
When we put a molecule in magnetic field and molecule then chemicaly equelent proton orientation in magnetic field with respect to the neighbouring proton
So the coupling between nucleas spin of neighbouring proton take place the phenomenon is called as a spin coupling and signal appear as multiplate
The spin -spin coupling explain by the following example - Bromo ethane
Similarly the spin of three proton in the Bromo ethane
Coupling constant:-
The distance between two peak of a multiplatealways remain constant it is known as coupling constant
Coupling constant denoted (j)
The unit of coupling constant is cycle/second or Hrz
Example -Bromo ethane
Coupling constant can be classified in following categories
1.Geminal coupling constant
2.vicinal coupling constant
3.long range coupling constant
1. Geminal coupling constant :-
Geminal proton are separated by two bond present of same carbon
The interaction between proton present on same carbon atom which have different chemical environment is known as Geminal coupling and coupling constant is known Geminal coupling constant
Geminal coupling constant is denoted by 2jhhor Jgemi
Geminal coupling constant is denoted is denoted
The value of Geminal constant may be negative or may positive
Genraly value of Geminal coupling constant is in the range 22 to 44 cps ( cycle per second )
The value of Geminal coupling constant depend of thita ( bond angle)
The relation of Geminal constant with bond angle can be represented following graph
The value of Geminal coupling constant also depends of electronegativity which is attached of carbon atom it is also depends on ./. S-character in hybrid orbital
2.vicinalcoupling constant :=
Vicinal proton present on near by carbon atom Vicinal proton are separated by three bond
The value of Vicinal coupling constant depends on dihedral angle
Vicinal coupling constant is denoted by Jvici
The relation of Vicinal coupling constant with dihedral angle is given by karpulse equation
The graph show that the Vicinal coupling constant have maximum at 0.to 180.
The value of Vicinal coupling constant we all ways positive
Then the value of Vicinal be increase
3. Long range coupling constant :-
If the distance between two proton are large them four bond in every difficult to observe coupling between them
In some molecule which contain pie system long range coupling is possible
As the distance between two proton increase then value of coupling constant decrease
If two proton are separated by two bond these for bond orientation as W-shape it is also called W-coupling
The value of the coupling constant is in depended from the external field
The NMR spectrum represent total chemical equelent proton present in the molecule
It is observed that proton, not observed a signal line the signal appear at multiplate splitting of in observed the region of splitting is spin -spin coupling
When we put a molecule in magnetic field and molecule then chemicaly equelent proton orientation in magnetic field with respect to the neighbouring proton
So the coupling between nucleas spin of neighbouring proton take place the phenomenon is called as a spin coupling and signal appear as multiplate
The spin -spin coupling explain by the following example - Bromo ethane
Similarly the spin of three proton in the Bromo ethane
Coupling constant:-
The distance between two peak of a multiplatealways remain constant it is known as coupling constant
Coupling constant denoted (j)
The unit of coupling constant is cycle/second or Hrz
Coupling constant can be classified in following categories
1.Geminal coupling constant
2.vicinal coupling constant
3.long range coupling constant
1. Geminal coupling constant :-
Geminal proton are separated by two bond present of same carbon
The interaction between proton present on same carbon atom which have different chemical environment is known as Geminal coupling and coupling constant is known Geminal coupling constant
Geminal coupling constant is denoted by 2jhhor Jgemi
Geminal coupling constant is denoted is denoted
The value of Geminal constant may be negative or may positive
Genraly value of Geminal coupling constant is in the range 22 to 44 cps ( cycle per second )
The value of Geminal coupling constant depend of thita ( bond angle)
The relation of Geminal constant with bond angle can be represented following graph
The value of Geminal coupling constant also depends of electronegativity which is attached of carbon atom it is also depends on ./. S-character in hybrid orbital
2.vicinalcoupling constant :=
Vicinal proton present on near by carbon atom Vicinal proton are separated by three bond
The value of Vicinal coupling constant depends on dihedral angle
Vicinal coupling constant is denoted by Jvici
The relation of Vicinal coupling constant with dihedral angle is given by karpulse equation
The graph show that the Vicinal coupling constant have maximum at 0.to 180.
The value of Vicinal coupling constant we all ways positive
Then the value of Vicinal be increase
3. Long range coupling constant :-
If the distance between two proton are large them four bond in every difficult to observe coupling between them
In some molecule which contain pie system long range coupling is possible
As the distance between two proton increase then value of coupling constant decrease
If two proton are separated by two bond these for bond orientation as W-shape it is also called W-coupling
The value of the coupling constant is in depended from the external field
Comments
Post a Comment
Please write comments