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IMG_0001_NEW_0020 - fl/ofe since the units are recipracal...

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_l .t dipoles attempt to align with oscillating microwave beam, as beam oscillates molecules rotate to keep dipole aligned. As molecules spin they bump into one another and friction generates heat. (ice does not melt in microwave!) Radiofrequency - lowest frequency, used in NMR and MRI (more later on this!) lnfrared Spectroscopy Radiation from l. = 0.8 to 100 pm (or 0.00008 to 0.01 cm) lR radiation interacts with molecular vibrations (stretching or bending) that result in a change in dipole moment of a molecule. Preferred unit is wavenumberv = 1/)" expressed in cm-1 lwavecycles/cm) Range of lR that is useful to organic chemists is 4000
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Unformatted text preview: fl,/ofe; since the units are recipracal cm 4AA0 crn'1 is Higher in energy than 4A0 cm'1 When we discuss covalent bonds (length and strength) the values we discuss are always the average. ln reality, bonds are continuously stretching and bending. With this in mind, consider a bond between 2 atoms like 2 balls on a spring that can stretch or compress. STRETCHES -6-f stretch (no change in dipole) ) symmetric I stretch I I I similar I rn energy ^6,.6-^+-:^ | lzooo cm-1; asymmetflc I stretch ) L.-.H .,jn €i \H {, r\ \H note. in H2 or N2 (etc.) there is no lR interaction J H-H : H no change in dipole...
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