Integration and Splitting
Integration
• Area under signal is proportional to the number of protons in the set
• RELATIVE AREA is calculated by computer
Integration
• Trace of spectrum is cut into sections above each signal to give integration values
Which proton set is this?
Integration
• You need to “set” the values• Here is a more realistic outcome
0246810PPM
This is the NMR for a C5H10O compound. What are the integration values?
72.3 143.572.1
434.2
Product Distribution by Integration• In a mixture, areas are also proportional to
number of protons• But they can by fractions
A
B B
C
D E
F
G
F
DE
C
G
A
B F
57%43%
Splitting
Splitting
• Shielding is also affected by magnetic fields of nearby nuclei
N + 1 Rule
• The signal for protons b is a quartet
• Signal b is “coupled” to the three protons labeled “a”
• Four possible affects on signal b• Summarized by this
simplification: n+1, where n = number of adjacent, nonequivalent protons
Splitting
Exchangeable protons
• If protons exchange, they are not coupled• If protons are not coupled, they will no show
splitting in signal• Typical for alcohols and acids
Label splitting for each proton set
OH
O O
OCH3
OCH3
Cl
OH
O Br Br
N+1 is a Simplification
• We learn it first because it applies to many molecules
• Assumes that all adjacent protons couple to an identical, measureable degree
• One exception: Aldehyde• We will learn a more robust
treatment after we master first principles
Very small coupling between these protons, even though they are adjacent
O
H
H H
(of ten singlet)
(of ten doublet)