[Ingeniosuccinimide]

Why does the 1H spectrum of isoprene have 5 signals instead of 4/6? I.e. why we can differentiate between two protons of one terminal double bond but not the another?

[sjb]

Why does the 1H spectrum of isoprene have 5 signals instead of 4/6? I.e. why we can differentiate between two protons of one terminal double bond but not the another?

What is the structure of isoprene (an IUPAC name, or a SMILES string..?)

[clarkstill]

http://www.sigmaaldrich.com/spectra/fnmr/FNMR010733.PDF

I'm guessing you are referring to the 2H peak at around 5.0 ppm? It clearly isn't a simple singlet, and you might get resolution between the two methylene H's on a higher frequency machine. Basically there isn't any fundamental reason why there aren't 6 signals, they are just coincidentally on top of one another ("isochronous").

[pgk]

Protons of the same carbon atom, might not be magnetically equal. So, take a look to the magnetic anisotropy chapter in a NMR-textbook and then, try to configure the splitting of all protons between the neighbor ones.

[pgk]

If something still is missing, think about long distance shift coupling through the double bond (allylic system).