Spin Spin Coupling

1. SPIN-SPIN SPLITTING
Dr. Vrushali Tambe
PES Modern College of Pharmacy
(For Ladies), Moshi

2. Outcomes
• Define spin-spin splitting (BT1)
• Understand the meaning and reason behind
spin-spin splitting (BT2)
• Predict the splitting pattern for the given
compound (BT3)
• Perform the structural elucidation of unknown
compound (BT5, BT6)

3. NMR Spectrum of Bromoethane
CH2CH3Br
How many signals?
What is peak height?
What is chemical shift?
What is the splitting pattern?
What is the value of couling constant?

4. Often a group of hydrogens will appear as a multiplet rather than
as a single peak.
SPIN-SPIN SPLITTING
Multiplets are named as follows:
Singlet Sextet
Doublet Septet
Triplet Octet
Quartet Nonet
Quintet Decet
This happens because of interaction with neighboring hydrogens
and is called SPIN-SPIN SPLITTING.
Spin spin splitting is a term that describes the magnetic
interactions between neighbouring, non-equivalent NMR-active
nuclei which will cause splitting of NMR signal.

5. C CH
Cl
Cl H
H
Cl
integral = 2
integral = 1
triplet doublet
1,1,2-Trichloroethane
The two kinds of hydrogens do not appear as single peaks,
rather there is a “triplet” and a “doublet”.
The subpeaks are due to
spin-spin splitting and are
predicted by the n+1 rule.
Triplet
Doublet

6. C C
H H
H
C C
H H
H
two neighbors
n+1 = 3
triplet
one neighbor
n+1 = 2
doublet
This hydrogen’s peak
is split by its two neighbors
These hydrogens are
split by their single
neighbor

7. 1 2 1
PASCAL’S TRIANGLE
1
1 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1
singlet
doublet
triplet
quartet
quintet
sextet
septet
octet
The interior
entries are
the sums of
the two
numbers
immediately
above.
Intensities of
multiplet peaks

8. SOME COMMON SPLITTING PATTERNS
CH2 CH2X Y
CH CHX Y
CH2 CH
CH3 CH
CH3 CH2
CH3
CH
CH3
( x = y )
( x = y )

9. • Chemical Shift is determined by Magnetic field
experienced by proton
• Magnetic field experienced by proton=
Applied Magnetic field + Local magnetic field

10. C C
HB H
C C
HB HA A
upfielddownfield
Bo
When we are recording NMR spectra of proton A, it sees its neighbor B aligned to it in 50% molecules….in
these molecules the magnetic field felt by proton A is augmented and it will required less magnetic field to
come to the resonance. Hence, it absorbs downfield.
Inn remaining 50 % molecules, proton A sees its neighbor B aginst to it….in these molecules the magnetic
field felt by proton A is decreased and it will required more magnetic field to come to the resonance. Hence, it
absorbs upfield.
50 % of
molecules
50 % of
molecules
At any given time about half of the molecules in solution will have spin +1/2 and the
other half will have spin -1/2.
aligned with Bo opposed to Bo
neighbor aligned neighbor opposed
+1/2 -1/2

11. C C
HA HB
C C
HA HB
one neighbor
n+1 = 2
doublet
one neighbor
n+1 = 2
doublet
HB can be
seen as a
doublet
HA can be
seen as a
doublet
Orientations
of HB
Orientations
of HA

12. C C
H H
H
C C
H H
H
two neighbors
n+1 = 3
triplet
one neighbor
n+1 = 2
doublet
methylene spins
methine spins
1:2:1 ratio
1:1 ratio

13. three neighbors
n+1 = 4
quartet
two neighbors
n+1 = 3
triplet
C C
H H
H
H
H
C C
H H
H
H
H
methyl spins
methylene spins
1:3:3:1
ratio
1:2:1
ratio

14. Protons are equivalent by symmetry
CH CHX Y
no splitting if x=y
Protons in the same group or chemically equivalent
usually do not split one another
C
H
H
H
Splitting is not seen if…..
If n+1 rule is followed we get first order spectra
Aromatic and alkene systems generally give complex non first order spectra

15. Test Yourself

18. NMR Spectrum of Bromoethane
CH2CH3Br

19. NMR Spectrum of 2-Nitropropane
CCH3 CH3
N
H
O O
+
-
1:6:15:20:16:6:1
in higher multiplets the outer peaks
are often nearly lost in the baseline

20. NMR Spectrum of Acetaldehyde
CCH3
O
H

21. Predict the splitting patterns of the following molecules:

22. Doublet
Septet
Triplet
Doublet
Singlet Quartet Triplet

23. Draw the following as per data
A. C3H5O; two triplet, 1 doublet
B. C4H8O2; three singlets
C. C5H12; one singlet

24. Thank You....