[davidenarb]

Hi all !

I would like to know how many signals we would expect for the chiral product R 3-methylhexane  in the 1H NMR spectrum.

Here's my attempt:

we have 3 CH3 groups, so we have 3 signals.
we have 3 CH2 groups, and they are not chemically equivalent, so we have 6 signals.
In addition to the H of the C3 carbon.
in total, we would expect 10 signals.

Am I correct?

thank you

[Borek]

Doesn't look correct to me - all these hydrogens are very similar and there will be a lot of splitting. IMHO you will get some messy multiplet.

I have a feeling you are mistaking 1H NMR with 13C NMR.

[davidenarb]

Doesn't look correct to me - all these hydrogens are very similar and there will be a lot of splitting. IMHO you will get some messy multiplet.

I have a feeling you are mistaking 1H NMR with 13C NMR.

Hi all !

I would like to know how many signals we would expect for the chiral product R 3-methylhexane  in the 1H NMR spectrum.

Here's my attempt:

we have 3 CH3 groups, so we have 3 signals.
we have 3 CH2 groups, and they are not chemically equivalent, so we have 6 signals.
In addition to the H of the C3 carbon.
in total, we would expect 10 signals.

Am I correct?

thank you

I was talking about hydrogens not carbons. Also, I didn't cover the 13C NMR, so I really mean 1H NMR

[davidenarb]

according to this website http://www.chemicalbook.com/SpectrumEN_589-34-4_1HNMR.htm , they found 9 different protons. I don't understand why it's not 10

[discodermolide]

Looking at that spectrum you'd be lucky to distinguish 1 never mind 9 signals

[discodermolide]

here is a calculated spectrum from ChemDraw:you can see that overlapping of signals reduces the number visible.

[davidenarb]

Looking at that spectrum you'd be lucky to distinguish 1 never mind 9 signals

haha I agree, but why 9 and not 10 ?

[davidenarb]

here is a calculated spectrum from ChemDraw:you can see that overlapping of signals reduces the number visible.

I still don't understand why we don't have 10 different protons

[discodermolide]

look at the chemical shifts they give, there are two signals with the same shift of 1.33 ppm, that makes 1 signal on the piece of paper.

[davidenarb]

look at the chemical shifts they give, there are two signals with the same shift of 1.33 ppm, that makes 1 signal on the piece of paper.

in the problem that I am working on, I don't have any shifts. I just have the compound, and I need to predict the number of signals

[discodermolide]

In an ideal world I would expect 7 signals. If they are doublets or whatever it does not matter.

[davidenarb]

this is so confusing! 

[discodermolide]

One set of signals for each different type of hydrogen.

[davidenarb]

Hi all
I found this useful website ( http://www.nmrdb.org/new_predictor ) that predict NMR spectrum, and it can also show you the different equivalent protons.
After drawing 3-methylhexane, there is indeed 10 different types of hydrogen

[discodermolide]

That is indeed useful, thanky.
In your case, look at the numbers, 7,8,& 9 have the same chemical shift, 0.871 ppm and will therefore appear as 1 signal. Protons 10 & 11 have the same shift, 1.282ppm, therefore will appear as 1 signal.
Same for 12 & 13, 15 & 16 and 17, 18 & 19, 20, and  21 & 22.
Six distinct groups of signals. And one by itself.