A compilation of the S—O symmetric and asymmetric stretching frequencies is given for a large number of compounds containing an —SO2— group. It is shown that a linear relationship betweenis valid for a large number of sulphuryl and polysulphuryl compounds and that the actual frequencies depend in a systematic manner on the electronegativities of the attached groups. These relationships have proved very useful in assigning and in some cases reassigning the S—O bands in the infrared and Raman spectra of a number of sulphuryl compounds. It is pointed out that there is a relationship between the SO2frequencies of some sulphonic acids and their acid strengths.The calculation of values for group electronegativities from the vibration frequencies of the P=O and SO2groups is discussed.