Tools of Organic Chemistry: Nuclear Magnetic Resonance (NMR) and Ir Spectrometry

Learn about the tools used by organic chemists to decifer unknown compounds!
Also a great review for organic chemistry exams.


Infrared (IR) Spectrometry: Works of using IR waves to vibrate the bonds in functional groups. IR Spec is often used to weed out what a molecule is not. IR Spec can also be used to watch the progress of a reaction. The frequency functional groups will absorb is dependent on the strength of the bonds between the molecules and the reduced mass (product mass/ sum masses).

Reading an IR Spec readout: The readout will be a graph of transmittance % as different wavelengths. Anything below 1500 is a readout of the single bonds and is generally not used except that it is called a finger print, meaning that this crazy looking portion of the graph (below 1500) is specific to that species of molecule.

In the area between 1500 – 2000  C=C (carbon carbon double bonds), C=O and C=N bonds show up

In the area between 2000 – 2500 CtripleC (carbon carbon triple bonds) and CtripleN bonds show up

In between 2500 – 4000 C-H, O-H and N-H bonds show up

A peak above 3000 means there is at least one unsaturated carbon.

Nuclear Magnetic Resonance: NMR is used to detect the nuclie of atoms by altering the magnetic environment around them. In the absence of a strong magnetic field the atoms will spin in random directions but an NMR machine can generate a very strong magnetic field which will align the atoms to all point in the same direction, and can measure the energy changes cause by aligning the spin of the nuclei. Sheilded vs. desheilded nuclei will give off different amounts of energy changing state.

In the NMR spectrum:

Between 0 and 50 will show C-C bonds and C-H bonds

Between 50 and 100 will show C-O single bonds and C-X (X being a halogen: F, Cl, Br or I)

Between 100 and 150 will show C=C

Between 150 and 200 will show C=O

The NMR spectrum is measured in parts per million (PPM)


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