How can I draw NMR splitting diagrams?
The general rule for
We draw a "splitting tree" for each proton or group of protons.
No Adjacent Protons
No splitting. Draw a single line.
1 Adjacent Proton
Draw 2 lines (a doublet) separated by
2 Adjacent Protons
From each line of the doublet, draw two more lines separated by
3 Adjacent Protons
From each line of the triplet, draw two more lines separated by
Repeat the process as many times as needed.
The relative intensity ratios are given by Pascal's triangle.
Here are some splitting patterns that you should be able to draw quickly.
AX doublet-doublet: -CH-CH-
AX₂ doublet-triplet: -CH-CH₂-
AX₃ doublet-quartet: CH₃CH-
AX₆ doublet-septet: (CH₃)₂CH- (an isopropyl group!)
Note: A septet often looks like a quintet with the wrong intensities, because the two outermost lines are so weak.
A₂X₃ triplet quartet: CH₃CH₂- (an ethyl group!)
Here's a video that gives an introduction to NMR splitting patterns.