Infrared (IR) Spectroscopy Characteristic Absorptions

Vocabulary flashcards covering characteristic infrared (IR) spectroscopy absorption regions and corresponding functional group features.

Alcohol O-H

broad and huge 3500-3200

Carboxylic acid O-H

3300 - 2250 ;

Very broad. swallows the C-H peaks.

Primary amine or amide $\text{N-H}_2$

Characterized by two sharp-ish peaks in the IR spectrum at $3400\,\text{cm}^{-1}$ and $3300\,\text{cm}^{-1}$.

Secondary N-H

Characterized by one peak in the IR spectrum at $\sim 3300\,\text{cm}^{-1}$.

Terminal alkyne $\equiv\text{C-H}$

3300

sharp and narrow

$$\text{sp}^3\text{ C-H}$$

Characterized by an IR absorption just below $\sim 3000\,\text{cm}^{-1}$ (everything has this).

Aldehyde C-H

two week peaks

2820 and 2720

$$\text{C}\equiv\text{N}$$

2250-2100

medium/sharp

$$\text{C}\equiv\text{C}$$

2250-2100

weak/sometimes missing

Ester C=O

~ 1750

Ketone, aldehyde, acid C=O

sharp at 1715

Conjugated C=O

lower region of $1690-1650\,\text{cm}^{-1}$.

Amide C=O

~1650

C=C

1650-1600

N-H bend

~1620

C-O

1300-1000