How can you distinguish E and Z isomers by nmr?

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Answer 1 · 2016-03-27T14:38:43

In 1,2-disubstituted alkenes, the coupling constants for the alkene hydrogens are always less for the #Z# isomer than for the #E# isomer.

Typical values for #J_"H-H"# are 15 Hz for (#E#)-alkenes and 10 Hz for (#Z#)-alkenes.

See, for example, the spectrum for (#E#)-1,4-dichlorobut-2-ene (#J = "15 Hz"#):

The coupling constant for(#Z#)-but-2-ene is 11 Hz.