[JohnTan]

Hello everyone,
I am currently highly confused about the H NMR spectrum. I am grappling with a question about describing the H NMR spectrum for 2,2-dimethylpropane and pentane. Now with 2,2-dimethylpropane, I was right in thinking there would be a single peak (as all of the hydrogen atoms are in the group CH3. However, with pentane I am inclined to say 2 peaks; for CH2 and CH3. The book, however says there are 3. Am I on the complete wrong track? please *delete me*

[stewie griffin]

Not all CH₂ groups in pentane are equivalent. Look at it: CH3-*CH2-#CH2-*CH2-CH3. The outside CH3's are equivalent since they are both in the same type of environment (that is they are next to a CH and nothing else) so they show up the same. The starred CH2 now is different from the #'d CH2. The #'d CH2 is next to TWO CH2 groups. However, the *'d CH2 is next to a CH3 and a CH2. Different environments means they will have different chemical shifts.
Now the *'d CH2's are both equivalent by the same logic as the methyl groups. Thus there should be three distinct signals (there will be more than three peaks in the spectrum b/c each signal will have it's own splitting pattern).