Question

In proton NMR does the 2 hydrogen attached to a carbon double have different environments.

For exam in 2 methylbut-1-ene it has 5 signals rather than 4 due go the double bond?

Thanks in advance.

Answer 1

Hydrogens on the same carbon (geminal) atom which is double bonded to the adjacent carbon atom are in different electronic environment, and thus are non-equivalent and have different resonance frequences.

Ha is cis to the ethyl group , while Hb is trans to the ethyl group.

Yes, there will be 5 signals in proton NMR spectrum as each of Ha and Hb will give a signal:

NMR spectrum can be found on the link: http://atb.uq.edu.au/molecule.py?molid=31858#panel-nmr