Deducing the structural formula from the NMR

[3dObject]

The answer to the following question is choice B. I really have no idea how this answer is made to come about. I thought a single spike meant the presence of a single functional group, but everything here is a hydrocarbon chain. Please advice.

[adrian]

Originally Posted by 3dObject

The answer to the following question is choice B. I really have no idea how this answer is made to come about. I thought a single spike meant the presence of a single functional group, but everything here is a hydrocarbon chain. Please advice.

There are some different analyses: IR, for functional groups, UV-VIS for multiple bonds and NMR for hydrogen atoms (mainly bonded with carbon). Because NMR signal is related with the spin of the hydrogen atom, different positions of signal appear in the spectra.

[Dan the Chemist]

Simply put, different resonances in NMR indicate different H environments.
Multiplet structure of resonances gives information about neighboring Hs.

You are told that the NMR spectrum consists of one singlet. This means that every single H must be in an equivalent environment.

The only one of those structures that has all its Hs in the same environment is B.

[Anand]

As Dan said,

we know that Cs bearing H atoms can only give a peak in NMR,

Middle two Cs doesnt have any Hs so no peaks from these middle two,

the remaining Cs are equivalent, i.e. each one surrounded by same no of Hs(here each H & Cs is equialent) and so same amount of hinderence experienced by both the Cs)

thats why only one peak is observed for both the carbons..

Anand