HOW TO APPROACH THE ANALYSIS OF A SPECTRUM
1. Is a carbonyl group present?
The C=O group gives rise to a strong absorption in the region 1820-1660 cm–1
(5.5-6.1 μ). The peak is often the strongest in the spectrum and of medium width.
You can't miss it.
2. If C=O is present, check the following types (if absent, go to 3).
ACIDS is OH also present?
- broad absorption near 3400-2400 cm–1 (usually overlaps C–H)
AMIDES is NH also present?
- medium absorption near 3500 cm–1 (2.85 μ)
Sometimes a double peak, with equivalent halves.
ESTERS is C–O also present?
- strong intensity absorptions near 1300-1000 cm–1 (7.7-10 μ)
ANHYDRIDES have two C=O absorptions near 1810 and 1760 cm–1 (5.5 and 5.7 μ)
ALDEHYDES is aldehyde CH present?
- two weak absorptions near 2850 and 2750 cm–1 (3.50 and 3.65 μ) on the right-hand
side of CH absorptions
KETONES The above 5 choices have been eliminated
3. If C=O is absent
ALCOHOLS Check for OH
PHENOLS – broad absorption near 3400-2400 cm–1 (2.8-3.0 μ)
- confirm this by finding C–O near 1300-1000 cm–1 (7.7-10 μ)
AMINES Check for NH
