Spectroscopy Flashcards
What can we do using NMR?
• Deduce number of atoms, of a particular element
• Deduce the position of these atoms within the molecule
• Infer useful information about what is around these atoms in the molecule.
• This allows you to work out the structure of an organic molecule.
When else can carbon’s be equivalent?
protons on neighbouring carbon atoms can also be equivalent if they are in exactly the same environment.
what do equivalent protons do?
protons on neighbouring carbon atoms can also be equivalent if they are in exactly the same environment
What does the peak of a phenyl group (the benzene ring protons) often appear as?
as one or more multiplets.
What is the key information for aromatic protons?
Aromatic protons have a chemical shift between 6.00 – 8.00 ppm.
• Refer to them as a multiplet and aromatic protons.
• Do not analyse the spitting pattern.
• Use integration (peak area) to deduce substitution on the ring.
What happens you measure an NMR spectrum for an alcohol like ethanol, and then add a few drops of deuterium oxide, D2O, to the solution, and then re-measure
the spectrum?
the −OH peak disappears. By comparing the two spectra, you can
tell immediately which peak was due to the −OH group.
What is this called and where can it also occur?
proton exchange and can also occur with hydrogen atoms attached to nitrogen or sulfur. Hydrogens are said to be ‘labile’ when attached to O, N or S
What are the functional groups involved?
ROH, ArOH, RCOOH, RNH2, RCONH2, RCH(NH2)COOH
What is the context of Picking out the –OH or NH peak; use of D2?
All alcohols are very, very slightly acidic. The hydrogen on the −OH group is donated to a lone pair on the oxygen of the D2O.
What do OH and NHx groups not do?
do not split and are not split by neighbouring environments
Why was tms added?
Tms is the standard for chemical shift measurements
