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Reactions of primary, secondary, and tertiary alkoxides of zirconium with acetyl chloride have been investigated and the following new compounds prcpared : ZrCI,,PrnOAc ; ZrC1,,2PriOAc ; ZrC1,(OPri) ,,PriOH ; ZrCl( OPri),,PriOH ; and ZrC1(OPri),. No hydrogen chloride was evolved in reactions involving Zr(OPri),,PrlOH and acetyl chloride even in the presence of excess of isopropyl alcohol, and ZrC1,(OPri) ,2PriOH was obtained by treating Zr(OPri) ,,PriOH with hydrogen chloride. Radical-interchange reactions involving chloride alkoxides of zirconium are demonstrated and mechanisms of radical interchange between chlorides and alkoxides of silicon, titanium, and zirconium are discussed.BRADLEY, HALIM, and WARDLAW (J., 1950, 3450) stated that reactions of acetyl chloride with certain new zirconium chloride ethoxides presented novel features; eg., an excess of acetyl chloride yielded the complex tetrachloride ZrCl,,EtOAc : ZrCl,(OEt), + 2AcCl+ ZrCl,,EtOAc + EtOAc. This reaction has now been investigated for Zr(OPri),,PriOH and Zr(OR), where R = Prn, n-octyl, CHEt,, and tert.-amyl. Zirconium 92-propoxide gave the crystalline complex ZrC1,,PrnOAc, analogous to that from zirconium ethoxide. However, the isopropoxide furnished a crystalline substance ZrC14,2PriOAc, which illustrates the important part played by the shape of the addendum (e.g., ethyl benzoate forms ZrC14,2EtOBz). It was not possible to isolate a pure reaction product from acetyl chloride and zirconium n-octyloxide although there is little doubt that a derivative of zirconium tetrachloride was initially formed. Similarly it was deduced that for zirconium tetra-1-ethylpropoxide replacement had not exceeded the trichloride stage. Finally it was found that zirconium tert.-amyloxide was much less reactive towards acetyl chloride than the other alkoxides, the order of reactivity thus being [Zr(OEt),; Zr(OPri),,PriOH ; Zr(OPrn), ; Zr(OC,H,,),]>Zr(OCHEt,),>Zr(O*CMe,Et),. I t is noteworthy that the more reactive 12-alkoxides are highly associated in benzene solution whilst the unreactive tert.-amyloxide is monomeric.A more detailed study revealed that zirconium chloride tri-tert.-amyloxide was formed much more readily than the dichloride di-tert.-amyloxide (see the Table where the mol. ratio of reactants is compared with the C1 : Zr ratio in the resulting zirconium compound).

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Absorption and fluorescence spectra of trans-1,1,4-triphenylbutadiene, trans-1,1,4,4-tetraphenylbutadiene (TPB), and trans-1,1,4,4-tetraphenyl-2-methylbutadiene (TPMB) were measured in an isopentane-methylcyclohexane mixture at room temperature and in rigid glass at 77°K. Absorption maxima exhibit a polarization red shift while fluorescence maxima exhibit a large blue shift upon freezing the samples at 77°K. Thus the intense blue fluorescence of tetraphenyl-2-methylbutadiene appears as a weak yellow fluorescence as soon as the rigid glass begins to melt. In these sterically hindered molecules the equilibrium configuration in the excited state is different from that in the ground state, and an intramolecular twisting relaxation process occurs before emission in fluid media. In rigid media and in the crystal, the twisting relaxation is slowed down, and emission originates from a Frank–Condon state which lies at higher energies. Quantum yield and energy of fluorescence of sterically hindered molecules in general are expected to be viscosity sensitive.