Not using NMR data

[kenhung123]

I've done a few exams and haven't came across any questions that required NMR data, yes I have came across NMR questions. They seem to be only used to identify number of hydrogen/carbon environments in questions...Is this just me or not??

[Mao]

The NMR data is only for referencing purposes. Generally you don't need to use them.

[stonecold]

Thank goodness.  I can barely even understand what the data book is talking about unless it is something really basic like R-CH2-CH3 or something like that.

[Martoman]

Yeah I never have ever had to use the databook for what it indicates. I always use it for the splitting/number of environments and can simply reason that the more to the right, more electronegative atoms are generally with the carbons or more shielding.

[stonecold]

Sorry, what is this about electronegativity and NMR?

How does it help to work out stuff, if you can be bothered explaining.

[shivesh.varmaxD]

first post in a long time.

my understanding is that if protons in a certain environment are near an electronegative group (a fluorine atom, for example), that environment's peak will be shifted upfield on the NMR spectrum to a higher chemical shift.

for example if protons in a methyl group is near a fluorine atom, that group's chemical shift which is normally at chemical shift 1.3 (databook) will be shifted upfield - perhaps to 2 or even 3ppm.

the theory behind it is based in the concept of 'deshielding' which you can read up on, but isn't overly important in my opinion.

hope that helps a bit.

[kyzoo]

Sorry, what is this about electronegativity and NMR?

How does it help to work out stuff, if you can be bothered explaining.

The closer protons are to an electronegative atom, the higher its chemical shift.

That's why R-COOH, in which the proton is near two highly electronegative oxygen atoms, has such a massive chemical shift of 11.5 or whatever.

[Martoman]

Yeah its like a bubble around the H's. The magnetic field is trying to "pierce" the bubble, and its harder to if there is more "shielding" from other molecules.

[kenhung123]

This is how I think of it. Electronegative=high attracting power of e's. H's near electro negative means the e's are drawn towards the electro neg atom. This means the signal is less e's from H's are far away from nucleus

[Greggler]

On the CSE 2010 exam there is a good q where you are given mass spec and NMR and infra red maybe. and you have to write down what sort of splitting is occuring on NMR and what each peak is represeintg and the proton shift. It's a fairly easy question but its been the only one ive seen of the sort. Where you actually have to use the whole R-CH3 and R-COO-R etc. things from the databook.