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H magnetic-angle spinning (MAS) NMR measurements have been performed on a number of crystalline titanias, and on amorphous silica-supported titania and titania-silica, with the aim of measuring the characteristic proton chemical shifts of hydroxy groups bound to titanias of different crystalline form. In the case of anatase, signals observed at 6 = 2.3 and 6.7 ppm correspond to terminal and bridging hydroxy groups, the results of deuterium exchange experiments (using D,O) and IR data supporting these assignments. For rutile, signals observed at 6 = 2.2 and 5.3 ppm are similarly assigned. Hydroxy groups bound to amorphous titania supported on silica (containing tetrahedrally coordinated Ti") are found to possess a characteristic chemical shift of 6 = 3.3 ppm. Deconvolution of 'H NMR spectra of titania-silica (containing 8 wt.% Ti) indicate the presence of a signal at 6 3.3 ppm, which is similarly assigned to hydroxy groups bound to tetrahedrally coordinated Ti", together with signals assigned to anatase and silanol groups. These observations are consistent with literature reports indicating the presence of two main titania phases in titania-silicas : an amorphous phase containing isolated Ti sites tetrahedrally coordinated by Si-0 and OH groups, and segregated nanodomains of TiO, (anatase or rutile).

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The n-π* transitions (absorption, circular dichroism, luminescence, linear and circular polarization of luminescence) of trans-β-hydrindanone (I) and trans-β-thiohydrindanone (II) are discussed. The C2 symmetry of I and II is taken into account with the aid of expressions that are derived for nonrigid molecules having a twofold axis of symmetry. This allows the absorption of I to be split into a part due to transitions polarized along the twofold axis (z axis) and a part due to x, y-polarized vibration-induced transitions. Accurate values for the electric and magnetic transition moments then are obtained. The vibrational structure of absorption and fluorescence and the latter's low degree of circular polarization are related to nonplanarity of the carbonyl group in the (n → π*)1 state. A larger nonplanarity probably is present in the triplet state of I. Circular polarization in the fluorescence was also observed when racemic I was excited with circularly polarized light. For the absorption of II, an upper limit is found for the electric transition moment and a lower limit for the magnetic moment. These give no indication that 3d orbits play an important part in the optical activity of thioketones. The luminescence at − 196°C and the longest wavelength part of the visible absorption band do not show circular polarization. They probably are singlet–triplet transitions. There is some evidence that the thiocarbonyl group is planar in the triplet and in the excited singlet state.

CoAPO molecular sieves of the structure types 5, 11, 16 and 34 have been investigated by means of electron absorption spectroscopy, temperature-programmed reduction and infrared spectroscopy in combination with pyridine adsorption, the purpose being to determine the amounts of framework and non-framework cobalt and to study the properties of incorporated cobalt with respect to stability, redox behaviour and associated acidic properties. It has been shown that framework and non-framework cobalt species exhibit different spectroscopic properties and can be distinguished from each other. The framework cobalt acceptance and the stability of the different structures decrease in the order CoAP0,-5 > CoAP0,-11 > CoAP0,-16 > CoAP0,-34. In stable structures such as 5 and 11, framework cobalt can perform reversible redox reactions Co" = C o ' ' ' , which are accompanied by changes in the concentration of Brsnsted and Lewis acid sites.

The dilute solution properties and association of hydrogenated poly(styrene-isoprene) two-block copolymers in decane and rrans-decalin have been studied by means of viscosity, diffusion and light-scattering measurements. Data were obtained for two samples with molecular weights of 48 000 and 80000, and both with a styrene content of 38%. In frans-decalin the normal behaviour of a non-associating polymer is found. Association occurs in decane with the formation ofcompact micelles, composed (at ambient temperatures) ofabout 80 molecules. In contrast to what is observed in other associating two-block systems, the transition to the completely dissociated state at elevated temperatures causes a drop ofthe intrinsic viscosity. Moreover, and this is not evident from the viscometric results, the diffusion and light scattering studies reveal that in the intermediate region between association and dissociation another kind of structure with very large dimensions is formed that exists over an extended temperature range. A qualitative description of the observed phenomena is given.* ) This cannot be true for very large N owing to the physical link of all branches with the centre, which limits the total volume.

The Bronsted acidity of H-mordenite and H-ZSM-5 samples of varying proton concentration has been studied using aqueous conductometric titration, IR spectroscopy, and aqueous potentiometrictitration. Good agreement is observed between Bronsted acid site concentrations determined by conductometric titration and IR measurements, while indirect potentiometric titration affords acid site concentrations consistently lower than those measured using the conductometric technique. This finding is rationalized on the basis that, in a conductometric titration, all the accessible Bronsted acid sites are directly titrated, whereas in the potentiometric procedure utilized, only those protons which can be ion-exchanged out of the zeolite are titrated. After allowing for the presence of extraframework aluminum in the zeolites (determined by27Al NMR), the measured acidity for H-mordenite is found to increase linearly with increasing Al content within the range 0-1.5 mmol Al/g but appears to reach a limiting value at higher Al concentrations. For H-ZSM-5, the experimentally determined number of Bronsted acid sites is also found to be linearly dependent on the Al molar fraction within the range measured (0-1.20 mmol Al/g). For both series of zeolite samples, the measured acidity is generally found to be less than the theoretical maximum calculated on the basis of an H+/Al ratio of 1.