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various olefins cannot presently be calculated with confidence, since values of IC2 and k2' are not so accurately known to warrant an infallible answer. The variation of the observed quenching efficiencies reflects the variation in the energy level separation between the triplet and the ground state of olefinic molecules through systematic structural changes (an alkyl-group substitution for a hydrogen atom bonded to an sp2 carbon Detailed discussions of this work and other related work will appear soon.
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Acknowledgment. E. K. C . Lee wishes to express his sincere appreciation for valuable comments and suggestions made by Professor W. Albert Noyes, Jr.
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(11) S. Sat0 and R. J. Cvetanovic, J . Am. Chem. Soc., 81, 3223 (1959). (12) N. L. Allinger and J. C. Tai, ibid.,87,2081 (1965).
DEPARTMENT OF CHEXISTRY UNIVERSITY O F CALIFORNIA
G. A. HANINGER, JR. EDW.4RD K. c. LEE
IRVINE, CALIFORNIA92664 RECEIVED MAY17, 1967
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The Location of Hydroxyl Groups in Hydrogen Y Zeolite
Sir: Spectroscopic studies of hydrogen Y zeolite have shown the existence of at least three types of structural hydroxyl groups with infrared frequencies near 3740, 3635, and 3540 ~ m - ' . ' - ~ Recent studies3v4have suggested that the 3540-cm-' band represents hydroxyl groups located in the SI or bridge positions in the structure. This conclusion was based on observations that olefins do not interact with the 3540-cm-' band whereas they did with the 3635-~rn-~ band, and that the 3635cm-l band, but not the 3540-cm-' band, was perturbed by the adsorption of molecules such as Nz, 02, CH4, Ar, and Kr. We have observed the infrared spectra of pyridine and water adsorbed on hydrogen Y zeolites which have been preheated to 450". Spectra for pyridine are shown in Figure 1. These spectra show that the 3635cm-l band is removed and the 3540-cm-' band is greatly diminished by interaction with pyridine a t 10 mm pressure. Heating to 200" with evacuation restores the 354O-cm-' band, showing that it interacts least strongly with the adsorbed molecules. Similar results have been reported by Liengme and Ammonia and deuterium oxide have also been found to interact with the 3540-cm-' band. It appears, then, that the 3540-cm-' band interacts with polar molecules but not with nonpolar molecules. The crystal structure of Y zeolite5 is such that if The Journal o j Physical Chemistry
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Figure 1. Spectra of hydroxyl groups on hydrogen Y zeolite: a, zeolite calcined and evacuated at 450'; b, zeolite exposed to pyridine at 10 mm and 25' for 2 hr; c, evacuation for 2 hr a t 200'.
hydroxyl groups were located in the SI positions, they would be unassessable to adsorbate molecules. Hence, the hydroxyl groups represented by the 3540-cm-I band must be in other locations. The suggestions of Eberly3 and White, et d l 4 that the two strong absorption bands at 3635 and 3540 cm-' represent different types of hydroxyl groups is supported by the pyridine adsorption data of Figure 1, which shows that these bands act independently. The exact location of the hydroxyl groups is not known a t this time, but it is probable that they represent different locations in the truncated octahedra sections of the structure. Further work is in progress to clarify the locations of these hydroxyl groups. (1) C.L.Angel1 and P. C. Schaffer, J . Phys. Chem , 69,3463 (1965). (2) B. V. Liengme and W. K. Hall, Trans. Faraday SOC.,62, 3229
(1966). (3) P. E. Eberly, presented before the Division of Petroleum Chemistry, 153rd National Meeting of the American Chemical Society, Miami Beach, Fla., April 1967. (4) J. L. White, A. N. Jelli, J. M. Andre, and J. J. Fripiat, Trans. Faraday Soe., 63, 461 (1967). (5) D. W.Breck, J . Chem. Educ., 41, 678 (1964).
UNIONOILCOMPANY OF CALIFORNIA UNIONRESEARCH CENTER BRE.4, C.4LIFORNI.4 92621 RECEIVED May 19, 1067
JOHN W. WARD
