Compound Class Group Absorption (cm -1 ) Appearance Comments acid halide C=O stretching 1815-1785 strong alcohols O-H stretching 3700-3584 medium, sharp free O-H stretching 3550-3200 strong, broad intermolecular bonded O-H stretching 3200-2700 weak, broad intramolecular bonded O-H bending 1420-1330 medium aldehyde C-H stretching 2830-2695 medium doublet C=O stretching 1740-1720 strong C-H bending 1390-1380 medium aliphatic ether C-O stretching 1150-1085 strong aliphatic ketone C=O stretching 1725-1705 strong or cyclohexanone or cyclopentenone aliphatic primary amine N-H stretching 3400-3300 medium alkane C-H stretching 3000-2840 medium C-H bending 1465 medium methylene group C-H bending 1450 medium methyl group C-H bending 1385-1380 medium gem dimethyl C-H stretching 3100-3000 medium C=C stretching 1678-1668 weak disubstituted (trans) C=C stretching 1675-1665 weak trisu