[noor123]

1) What is the difference between Off resonance, broadband decoupling and regular spectrum?  what type of different information is given?

2) How can you see ona C-NMR spectra if there are for example 4 oxygens (C7H12O4) how would it look if it was two esters on the spectrum. And how can i know that there are 2 and that they are identical? as in there is symmetry in the structure? 

[discodermolide]

A regular ¹³C-NMR is normally broadband decoupled. So only a single peak is observed for each carbon in the molecule. This is done by irradiating the entire frequency range which eliminates the coupling between H and C.
Off resonance is where the frequency of irradiation does not quite correspond to that of the signal. This allows the observation of the H-C coupling patterns. So a for a CH₃ group the ¹³C would appear as a quartet.
The ¹³C cannot really provide any information as to the number of C atoms as the integral does in an 1H NMR.
So if you suspect that your molecule is symmetrical then the spectrum should be relatively simple. You will need to combine this info with other NMR data in order to assess the symmetry of the system. Of course if the esters are different, say methyl and benzyl then you will be able to distinguish them in the ¹³C NMR.

[noor123]

ok and what about when the integrations are not given in H-NMR? how do i know how many protons the peaks represent? 

[Babcock_Hall]

I used to make photocopies of my spectra and cut and weigh the paper peaks.

[noor123]

what?

[discodermolide]

Yep, I used to do that as well. In the days before proper peak integration.

[Babcock_Hall]

I photocopied and possibly enlarged the NMR spectrum.  Then I took a razor blade and sliced out the peaks.  Then I weighed the paper I had sliced out.  Some people gave me the impression that it actually gives better results than electronic integration.  I don't have a strong opinion on that subject.

[discodermolide]

It probably does because the integral is a sigmoid curve and where do you actually measure the straight part?

[noor123]

ok wow haha i thought you were joking before. But thats cool! So just emailed my teacher and she said you can use a ruler and estimate the ratios ...

[discodermolide]

It goes by area under the curve which is directly proportional to the number of H atoms, I suppose you could draw a triangle round it and work out the area.