Transition experimental procedures

The basis for all calorimetric measurements is the determination of heat capacities. In the absence of any other transition, the DSC curve represents the change in the heat capacity of the sample over the experimental temperature range [5,24]. Detailed descriptions of experimental procedures and data treatment for using DSC to measure heat capacities are available [1,2,5,25-29] A simplistic approach is given below. 

A significant decrease in reactivity was observed when the IV-aryl zinc enamide generated from 4-methylaniline was used. It was suggested that this 2-methyl effect on reactivity may arise from a steric effect contributing to the conformational stabilization of the transition state. These recent results have thus greatly expanded the scope of the so-called olefinic aldol condensation as the experimental procedure is quite simple and applicable to a variety of monosubstituted or aqa-disubstituted alkenes. 

Eressure is determined by the water vapor partial pressure, which is carefully ept at saturation with respect to the equilibrium vapor pressure of water at the droplet temperature so that the droplets neither grow nor evaporate. Depending on the temperature of the droplets this sets the minimum pressure at 4 to 20 Torr. The transit time of the droplets through the reaction zone is short, on the order of a few milliseconds, in order to avoid saturation of the trace gas in the liquids. Experimental parameters are computer monitored. The details of the technique and of the experimental procedures are discussed in reference (2). 

Although the addition of catalytic amounts of transition metal complexes and salts results in clear benefits in many Sml2-mediated reactions, the mechanistic basis for their effect is unknown.54 Examination of the experimental procedures utilising catalytic amounts of Nil2 shows that, in most cases,... 

Early self-consistent field molecular orbital (SCF-MO) studies on PH3, PF3, and PMe3 by Hillier and co-workers 123, 144) predicted ionization potential data which were in good agreement with the experimental values determined by UV photoelectron spectroscopy 241). More recently, the electronic structures of these phosphines have been reexamined 67, 366). Self-consistent multipolar Xa calculations (SCM-Xa-DV) by Xiao et al. 366) give excellent agreement between the theoretical and experimental ionization energies. When the transition-state procedure is used, the first ionization potentials of 10.39,8.41, and 12.19 eV for PH3, PMe3, and PF3 are calculated compared with the experimental values of 10.58, 8.58, and 12.27 eV (Fig. 10). 

While the dilatometer method is the preferred method of determining the glass transition temperature, it is a rather tedious experimental procedure and measurements of Tg are often made in a differential scanning calorimeter (DSC). In this instrument (18), the heat flow into or out of a small (10-20 mg) sample is measured as the sample is subjected to a programmed linear temperature increase (typically 10 C/min). The heat flow is proportional to the specific heat of the sample. At the glass transition, there is an increase in the heat flow into the sample due to the increase in specific heat at this point. Values obtained in this manner are only a few degrees higher than the dilatometer values. 

The polysiloxanes were characterized by Fourier transform-IR (FTIR) spectroscopy, H and Si NMR spectrometry, and by GPC. AC conductivities of the polymer electrolytes were measured under dry helium by using an automatic capacitance bridge (General Radio Corporation). Glass transition (Tg) and melt (TJ temperatures were recorded on a differential scanning calorimeter (Perkin Elmer DSC-4). More detailed experimental procedures are published elsewhere (9, 12). 

Two temperatures for the thermochromic transition of PDHS in solution have been reported -24 (6) and -31 (7) °C. The difference between the two measurements is probably due to differences in material polydispersity and experimental procedures 10). If the light-scattering measurements were made at temperatures above the thermochromic transition and if the transition is first order, a change in s is not expected. Certainly, the dramatic increase in the scattering intensity observed at low temperatures is the result of the ordered phase precipitating from solution. However, whether the UV thermochromic transition occurs before the appearance of an ordered phase... 

Transition metal ion-exchanged faujasites CuY, PdY and HPdY (metal content in weight% indicated as suffix), activated at 623 K (CuY) or 723 K (PdY, HPdY), respectively, in an oxygen flow of ca. 20 ml/min were used as catalysts. Details about preparation of the zeolite samples as well as experimental procedures are reported elsewhere [4]. The home-made flow apparatus was equipped with an analytical tube for chlorine detection from Draeger, Liibeck,... 

---