Quiz 5 Flashcards
What does NMR stand for?
Nuclear magnetic resonance
What does NMR spectroscopy depend on?
The ABSORPTION OF ENERGY when the nucleus of an atom is excited from its lowest-energy spin state to the next higher one
How does a proton alone differ from a proton in an organic molecule when exposed to an external field?
A proton alone feels the full strength of the external field
A proton in an organic molecule responds to both the external field and any local fields within the molecule
What is the definition of ‘shielded’?
A proton is said to be shielded when the net field felt by a proton in a molecule will always be less than the external field
What is the definition of ‘deshielded’?
this describes the decreased shielding of one proton relative to another
Compare upfield protons with downfield protons
A more shielded proton absorbs radiation at HIGHER field strength
A less shielded proton absorbs radiation at a LOWER field strength
In shielded protons: the magnetic field experienced by the nucleus will be less than that applied and the precessional frequency will also be less for these shielded protons. Therefore, the external magnetic field strength must be increased to increase the precessional frequency and cause resonance. Thus, the signal for a shielded proton will appear at higher magnetic field strength.
Downfield protons are _______ shielded
less
Upfield protons are ________ shielded
more
Order chemical shifts of Hydrogens attached to common functional groups
- carboxylic acid: o=c-oH
- aldehyde: o=c-H
- aryl: Ar-H
- phenol: Ar-oH
- vinylic: c=c-H
- alcohol: r-oH
- alkyl chloride: cl-c-H
- alkyl bromide: br-c-H
- terminal alkyne: c≡c-H
- amine: r2n-H
- benzylic: arC-H
- allylic: c=c-c-H
- o=c-c-H
- n≡c-c-H
- alkane: cH, cH2, cH3
What does the number of signals tell us in an 1H NMR spectra?
how many different kinds of protons there are/how many nonequivalent protons there are
What does the intensity of the signals tell us in an 1H NMR spectra?
the relative ratios of the different kinds of protons
What does the multiplicity/splitting of each signal tell us in an 1H NMR spectra?
how many protons are vicinal to the one giving the signal
what is the meaning of vicinal protons?
protons on adjacent carbon atoms
What is the meaning of geminal protons?
protons attached to the same carbon atom
How do you calculate the ratio of your product: contaminant?
- pick a signal from the product molecule and divide integration number by the number of H atoms
- do the same for the contaminant/impurity
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