March 26, 2008
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs
The second-order effects (also known as tilting or roofing) exhibited by multiplets can be used to identify multiplets coupled to each other.
The 1H NMR spectrum below illustrates an example of strong coupling among three multiplets. The peak intensities across Multiplets A and B are different, that is, the peak on the right side of the multiplet is higher in intensity than the peak on the left side. The purple arrow illustrates a tilt towards the right side for both multiplets. Multiplet C shows an opposite tilt, i.e. to the left side. Multiplets that tilt to form a roof are most likely related protons, and thus are in proximity of each other. Therefore, one can say that Multiplets A and B are coupled to Multiplet C.
Although the field strength and coupling constants impact the amount of tilting, generally the closer the multiplets are the more pronounced is the tilting.