S3.2.10 Proton nuclear magnetic resonance spectroscopy (1H NMR) (HL)

[@susheelkona1]

Doesn't it say in that table you put up that the CH3 proton corresponds to a chemical shift of 0.9-1.0? Why did you put it at 2 at 1:18? Thanks

[@MSJChem]

It is due to a phenomenon called deshielding. Knowledge of this is not required in IB chemistry but it is useful to know. "Deshielding: The electrons around the proton create a magnetic field that opposes the applied field. This reduces the field experienced at the nucleus and therefore decreases the frequency required for the absorption. Therefore the chemical shift (delta /ppm) will change depending on the electron density around the proton. Since electronegative groups decrease the electron density, there will be less shielding (ie. deshielding) and the chemical shift will increase." www.mhhe.com/physsci/chemistry/carey5e/Useful/nmr.html#Deshielding

[@susheelkona1]

Thanks! Does this mean that the CH3 proton will always be present at 2? There was a question in the Pearson textbook that expected us to assume the peak at 2.0 referred to a CH3.

[@MSJChem]

+Susheel Kona In most cases, yes. You can assume that the CH3 will have a peak higher than the value in the data booklet.

[@susheelkona1]

Thank you so much! You're way better than any chem teacher I've ever had!

[@MSJChem]

+Susheel Kona Glad I could help.

[@ba-ze3fl]

how do you know that the OH lies at around 3 from it's 1-6 value 1:42

[@MSJChem]

It’s a hard one to figure out because of the large range. You can do it by a process of elimination.

[@dayyanali1946]

Hi Mr Jones, I was wondering if you have videos on topic 11.2 as I have been unable to find them on your playlist for topic 11/21.

[@MSJChem]

Unfortunately I don’t have videos on topic 11.2 because it is all to do with graphing.

[@dayyanali1946]

@@MSJChem Thank you for getting back to me.