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)