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NMR QUESTIONS AND ANSWERS
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An NMR spectrum is a graph showing ______. ✔✔energy absorption frequencies and intensities for a sample in a magnetic field.
4 things to look at in an NMR spectrum. ✔✔1.) The number of signals
2.) The position of the signals
3.) The area under the signals
4.)The multiplicity (splitting pattern) of each signal.
What does the number of signals on an NMR spectrum indicate? ✔✔How many different sets of protons there are in the molecule.
What does the position of the signals along the X-axis in an NMR spectrum indicate? ✔✔The position tells us about the magnetic environment of each set of protons, arising largely from the electron density in their environment.
COME BACK AND MODIFY THIS AFTER SECTION 9.2, TOO VAGUE.
What does the area under a signal on an NMR spectrum indicate? ✔✔How many protons there are in the set being measured.
MAYBE MODIFY THIS TOO AFTER SECTION 9.2.
What does the multiplicity of a signal indicate on an NMR spectrum? ✔✔Indicates the number of protons on atoms adjacent to the one whose signal is being measured.
Chemical Shift ✔✔The position of the signal along the X-axis of an NMR spectrum. gives information about the structural environment of the nuclei producing that signal.
ADD A CARD TALKING ABOUT THAT STUFF FROM QUESTION 2 THAT PATRICK
KNEW. ✔✔SAME MOLECULE AND ENANTIOMERS INDICATE IDENTICAL
CHEMICAL ENVIRONMENT, DIASTEREOMERS OR COMPLETELY DIFFERENT
MOLECULES INDICATE DIFFERENT CHEMICAL ENVIRONMENTS.
OR SOMETHING.
Alkene Hydrogen (hydrogen on a sp2 carbon) chemical shift ✔✔4-6.
Secondary alkyl halide (oxygen, chlorine, bromine, iodine) hydrogen chemical shift ✔✔3-
Secondary alkyl halide (nitrogen, sulfur) hydrogen chemical shift ✔✔2-
Hydrogen that is cis/trans to an O,N, CR2 hydrogen chemical shift ✔✔1.5-2.
All alkane hydrogens chemical shift ✔✔0.8-1.
Number of peaks in a signal from vicinal coupling= ________________ ✔✔n+1, where n = vicinal hydrogen atoms in different chemical environments
H's and C's have two spin states: ✔✔+1/
-1/
Applying a magnetic field to protons or hydrogens (Bo) produces two spin orientations: ✔✔- spinning with the applied magnetic field
-spinning against the applied magnetic field
6 steps to solving NMR spectra ✔✔1.) If molecular formula is given, determine number of DBE to help determine what groups must be present.
2.)Count the number of signals to determine how many distinct environments are in the molecule.
3.)Use your knowledge of the pink graph to corrolate chemical shifts with possible structures.
4.) Determine the relative area of each signal as compared to the area of other signals to determine the relative number of protons producing the signal (this is typically provided for you.)
5.)Interpret the splitting pattern for each signal to determine the number of hydrogens on adjacent carbons.
6.) Using all of the above, sketch possible molecular fragments, and then join these fragments to create a molecule consistent with the data.
Hydrogens on hydroxyls, and other electronegative atoms, will _______________________ with other, neighboring hydrogens ✔✔-Not couple (no splitting)
Exchangable protons ✔✔-protons on electronegative atoms that are easily exchanged between molecules
