The vibrational spectra of sodium dodecylsulphate [formula omitted] hydrate (α-phase)

• Published in: Spectrochimica acta. Part A: Molecular spectroscopy 1974, Vol.30 (1), p.117-124
• Main Author: Thompson, W.K.
• Format: Article
• Language: English
• ISSN: 0584-8539
• DOI: 10.1016/0584-8539(74)80216-3

Infrared and Raman spectra of crystalline sodium dodecylsulphate 1 8 hydrate (α-phase) have been recorded. The spectra favour the spce group C 2 h 4 and not C s 2. The polarizing properties of a grating spectrophotometer have been used to show that part of the water of crystallisation is hydrogen bonded, by one OH group only, to the ether-type oxygen atom of the anions. The orientation is discussed. Only one anion is hydrated per asymmetric unit. The second type of hydrate water is probably bonded, via its oxygen atom, to the cations in an isotropic orientation. Absence of any dichroic ratio differing from unity for the hydrocarbon chain absorptions, shows that the hydrocarbon chains are rotating even at 37°C. Presence of the theoretical number of bands for the group frequencies shows that intermolecular coupling of the 4-anions of the sub-cell occurs, so that rotation must be in cogwheel fashion, essentially preserving C 2 h factor group symmetry. Apparent absence of progression bands indicates that the rotation is not particularly rigid along the length of the alkyl chains.