•  Alcohols form hydrogen bonds between the hydroxyl oxygen of one molecule and the hydroxyl hydrogen of another. These bonds are variable in length (though they are usually rather longer than normal covalent O–H bonds) and they slightly weaken the true covalent O–H bonds by varying amounts. Alcohols thus give a rounded absorption at about 3300 cm^-1. Carboxylic acids (RCO₂H) form hydrogen-bonded dimers with two strong H bonds between the carbonyl oxygen atom of one molecule and the acidic hydrogen of the other. These also vary considerably in length and strength and usually give very broad absorbances.

•  In the double bond region, there are three important absorptions, those of the carbonyl (C=O), alkene (C=C), and nitro (NO₂) groups. All give rise to sharp bands: C=O to one strong (i.e. intense) band anywhere between 1900 and 1500 cm^-1 ; C=C to one weak band at about 1640 cm^-1; and NO₂ to two strong (intense) bands in the mid-1500s and mid-1300s cm^-1. Carbonyl and alkene clearly have one double bond each and gives rise to only one band each. In the nitro group absorptions for symmetrical and antisymmetrical stretching vibrations can be seen. As with NH₂ , antisymmetrical vibration occurs at higher frequency (>1500 plus cm^-1).

•  The region below 1500 cm^-1 is where the single bond vibrations occur. The atoms C, N, and O all have about the same atomic weight and C–C, C–N, and C–O single bonds all have about the same strength. Hence here the characteristic vibrations for these bonds are difficult to detect. However, this region below 1500cm^-1 is called fingerprint region because it is the characteristic of a particular compound.