3I‘ay, 1961
S P E C I F I C RTOLECULAR INTER.4CTIOSS I N
of water listed in Table IT’ is consistent with the view that the orienting species is the molecule itself formed by the breaking of hydrogen bonds and not a “po1ymer.’’11,16The negative values of A#* for the glycine solutions indicate the rotation of domains formed by cooperating molecules. The entropy of activation decreases with increasing concentration except between the 0.75 and 1 M (16) E. H. Grant, J. Chem. Phys., 2 6 , 1575 (1937).
RIGIDh I E D I i
88,j
solutions where the entropy increases. This can be explained by the partial disruption of the rotating domains by the additional glycine molecules. However, the errors involved in calculating the entropies of activation are such that the increase observed may be fictitious. Acknowledgment.-The authors wish to thank Mr. Ralph E. Hiatt for his valuable discussions and suggestions.
INFRARED ET’IDENCE OF SPECIFIC MOLECULAR INTERACTIONS I N RIGID MEDIA AT LOW TEMPERATURES BY G. ALLEN,A. D. KENNEDY AND H. 0. PRITCHARD Department of Chemistry, University of Manchester, Manchester I S , England Received December BS, 1960
In a n experiment designed to trap and study the absorption spectrum of the methyl radical in the 3000 cm.-l region, a spectral feature was observed having many of the expected properties, but which was eventually found to be due to a specific interaction between ethane and di-t-butyl peroxide. Subsequently, a variety of similar interactions were found between other pairs of stable molecules.
Di-t-butyl peroxide has a number of attractive features as a source of methyl radicals. The thermal decomposition into two acetone molecules and two methyl radicals is clean and takes place at quite low temperatures. Furthermore, in the 3000 cm.-l region the absorption intensities of the undecomposed peroxide and of the product acetone are an order of magnitude less than the absorption intensity of ethane, and of that to be expected for the methyl radical. Under suitable conditions, therefore, it would only be necessary to look for the methyl spectrum superimposed on the ethane absorption which must always be present. CFzClzmas chosen as the matrix because it is inert, it has no absorption in the 3000 cm.-l region, and it forms a clear glass which is rigid a t 77OK., but which becomes less rigid before the melting point (l15°1
