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Organic Chemistry I · Problem type
Which bond does the IR band show?
Use this for “A spectrum has a strong, sharp band at 1720 cm⁻¹ and nothing above 3000. Which functional group is it?”
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Which bond gives the band named on each card?
Tap a card, then tap its group.
Read the region first, then the shape: broad bands above 3000 are O–H, a strong sharp one near 1700 is C=O.
Assumptions
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Wavenumbers are in cm⁻¹ and the axis runs from 4000 on the left to 400 on the right; a band is a dip in transmittance.
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Stiffer bonds and lighter atoms absorb at higher wavenumbers: triple bonds above double bonds, X–H stretches highest.
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Hydrogen bonding widens an O–H band; a strong change in dipole, as in C=O, makes a band strong.
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Almost every organic compound has C–H bands near 2900, so look past them to the band that names the group.
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