Infra-ret1 spectra were obt,ained from anhydrons and hydrated sulphonic acids, as well as of the deutcratecl benzenesnlphonic acid. Following assignments of bands characteristic of the sulphonic acitl group are proposed: v(OH) 2900 and 2350 cm-l, u,,(SO,) 1350 cm-', v,~(SO,J 1160 cm-l, r(W) 900 cm-', wit,h very small tleviations. The spectra of hytlratecl srdpk.onic acids arc interpretetl in terms of superposition of the spectra of the SO, group ant1 the H,O+ ion. 'l'he positions of the v,(M),) ant1 the v,~(SO~) bands in sulphonic acitls ant1 t,heir derivatives are hriefly tliscussed.
'l'he bantls tlue to the stretching of the single S-O bonds in aliphatic sulphites were fount1 to appear bet,ween 690 and 560 cm-' whereas the analogous bands in the spectra of the corresponcling slllphates were found at slightly higher frequencies, but were difficult to separate from thr bands t111e to the aliphatic part of the molecule.
('URREKT investigations of the hydrogen bonding and the nature of the sulphuroxygen linkages in sulphonic and sulphinic acids have required the knowledge of the absorption frequencies connected with the sulphur-oxygen bonds in these and related compounds. The existing literature has been recently reviewed by BELLAMY [l]. and only a few papers have been published later. However, adequate presentations of sulphonic acid spectra seem to be lacking, and so are the assignments of infra-red bands due to the stretching of S-O bonds. These two subjects will be dealt with in the present paper.