The Four Factors of Proton NMR:
0.06
5
0.06
0.06
4
3
PPM
0.36
0.12 0.18
2
1
0
1. Symmetry: How many different types of protons are in the molecule? Each signal
represents a chemically different proton.
0.06
5
0.06
0.06
4
3
PPM
2
0.12 0.18
0.36
1
0
2. Chemical Shift: What type of protons are in the molecule, as determined by the value
on the X-axis.
1
0-2 ppm
alkyl group H's
2-5 ppm
H-O
0.06
5
3-5 ppm
H-sp3C-(O,N,X)
0.06
0.06
4
3
PPM
0.12 0.18
2
0.36
1
0
3. Integration: How many of each type of proton?
Divide each calculated area by the smallest value
0.06
5
0.06
0.06
4
3
PPM
2
0.12 0.18
0.36
1
0
4. Splitting Patterns: N+1 Rule
N+1 Rule – The (original) signal of a proton (or set of equivalent protons, as determined
by integration), with N number of protons on an adjacent carbon atom, will be split into
N+1 peaks in the final signal on the spectrum.
2
0.06
5
0.06
0.06
4
3
PPM
0.12 0.18
2
0.36
1
0
Assembling your fragments requires up to three pieces of information: Integration (tells
you the number of protons in the actual signal), Splitting Pattern (tells you how many
protons are next door) and Chemical Shift.
Set up a table:
Chemical Shift
Integration Splitting Pattern
Fragments
Drawing “Fragments” is the last part that needs to be discussed. These Fragments are
the actual molecular pieces that are found inside the organic molecule the NMR
represents. Consider a signal that integrates to 1H and is a quartet? What molecular
fragment produces a 1 proton signal that is split into four peaks? Integration tells you
how many of each type is present so 1H (CH, OH, NH). The Splitting Pattern is a quartet
(four peaks, N+1=4, N=3).
CH-CH3
signal we are looking at: three adjacent protons,
integrates to one proton as seen by the quartet
splitting pattern
Let’s analyze what we’d expect to see for some molecules.
CH3-CH2-Br
3
And this is what it looks like:
0.24
0.36
3
2
PPM
1
0
Now evaluate this one:
Br
H3C
H
CH3
And check out the proton NMR:
0.08
0.48
3
2
PPM
1
0
OH
H 3C
CH2 C
H
CH3
4
0.08
0.16
0.08
5
4
3
0.24
2
PPM
0.24
1
0
Notice how sometimes peaks can overlap with peaks
Br
H3C
CH2 C
H
CH3
0.45
0.09
3
2
PPM
0.27
1
0
5
Proton NMR Problems:
1. C2H5Br
0.24
4
0.36
3
2
PPM
1
0
2. C3H7Cl
0.12
4
0.18
0.12
3
2
PPM
1
0
6
3. C4H9I
0.08
4
0.25 0.17
3
0.23
2
PPM
1
0
4. C4H8Cl2
0.20 0.10
4
0.19
3
2
PPM
0.30
1
0
7
5. C5H11Br
0.12
0.36
0.12 0.06
4
3
2
PPM
1
0
6. C6H14O
0.05
4
0.05
0.45
0.15
3
2
PPM
1
0
8
7. C5H11Br
0.66 0.22
3
2
0.33
1
PPM
0
8. C8H10
0.35
8
0.14
7
6
5
4
PPM
3
0.21
2
1
0
9
9. C9H11Cl
0.10 0.10
8
0.05
7
6
5
4
PPM
0.30
3
2
1
0
10. C9H12
0.08
8
0.24
7
0.16 0.24
6
5
4
PPM
3
0.24
2
1
0
10
11. C10H13Cl
0.20
8
0.08
7
6
5
4
PPM
0.24
3
2
1
0
12. C11H16
0.45
8
0.18
7
6
5
4
PPM
3
0.81
2
1
0
11