CH 9-5: NMR Topic 3 - “Signal Splitting”
•The magnetic field of a specific H nucleus will be
“influenced” by the H nuclei on adjacent carbon atoms.
This causes the single line of a H signal to be “split” into
2, 3, 4, or more lines.
N + 1 Rule to predict 1H NMR signal splitting:
•If “N” is the total number of H’s on all carbons adjacent to
a specific H, then the signal from H will be “split” into N + 1
lines.
CH3
C
CH3
C
H
H
N + 1 = signal splitting
N + 1 = signal splitting
3 + 1 = 4 (quartet)
1 + 1 = 2 (doublet)
NMR “Signal Splitting” for observed H
N = total of all H’s directly adjacent to H:
N=0
N+1 = 1
singlet (s)
N=1
N+1=2
doublet (d)
N=2
N+1=3
triplet (t)
N=3
N+1=4
quartet (q)
N>4
N+1>5
multiplet (m)
N + 1 = signal splitting
H
H C
C
H
H
C H
Example: Isopropylmethyl ether
(a)
•How many signals?
•What is the signal splitting?
(b)
(c)
(a)
H nuclei
# protons
Splitting
n+1 rule
(a)
6
d
(b)
1
m
(c)
3
s
Isopropylmethyl ether
(a)
(c)
(b)
(c)
(a)
(b)
(a)
CH 9-5: NMR Topic 3 - “Signal Splitting”
•You should be able to answer the following question:
Complete the following table for each set of protons in the
molecule shown below:
H nuclei
# protons
Splitting
n+1 rule