Dissociation temperatures for

The temperatures at which hybridizations and washes are carried out is estimated by using the empirically derived formula Td (in °C) = [2 X (A + T) + [4 X (G + C)] to calculate the approximate dissociation temperature for oligonucleotides.18 In our experience dissociation temperatures predicted by this formula are quite accurate. However, we have observed situations where optimal results are obtained at temperatures 2-3° different from those predicted. Experimental calibration of the dissociation behavior of each oligonucleotide used should be performed as discussed below. 

To study the complexation selectivity of sodium iodide for the linear pentamine isomer, n-HMTP (Compound 7), and not the branched isomer (as in the analogous tetramine separation), both n-HMTP Nal and iso-HMTP Nal were prepared and studied. No substantial difference in solubilities of the pentamine-sodium iodide complexes in benzene could be observed. However, the stability of n-HMTP Nal in benzene seemed to be appreciably greater than that of iso-HMTP Nal in the same solvent. The latter complex dissociated in benzene to give free iso-HMTP and insoluble sodium iodide at 40 °C. The corresponding dissociation temperature for n-HMTP Nal in benzene was 72°C. The complexation selectivity found by combining N-permethylated TEPA with sodium iodide may be rationalized if the above results indeed were to reflect a difference in the relative stabilities of the two complexes. 

Wendlandt (290) studied various mercury(I, II) compounds using DTA/ DSC and other TA techniques. The DTA/DSC curves of the yellow and red forms of mercury(II) oxide are shown in Figure 7.29. The initial procedural AT deviation temperature (A7J) was about 475°C for the yellow form and, as expected, 550°C for the red form. The minimum procedural AT temperatures (A7, ) were 575 and 655°C for the yellow and red forms, respectively. Using the DSC data, A7J and ATm values of450 and 550°C, respectively, were found for the yellow form. In both the TG and DTA/DSC curves of the yellow and red forms of mercury (II) oxide, the lower procedural dissociation temperatures for the yellow form are consistent with a decrease in particle size. It is well known that a reduction in particle size of a compound such as this lowers the 7J (or A7J) values. The extent of the lowering, however, cannot be predicted. 

Seeley J V, Morris R A, Viggiano A A, Wang FI and Flase W L 1997 Temperature dependencies of the rate constants and branching ratios for the reactions of Cr(Fl20)g 3 with CFIjBr and thermal dissociation rates for CI (CFl3Br) J. Am. Chem. Soc. 119 577-84... 

Direct dissociation reactions are affected by surface temperature largely tlirough the motion of the substrate atoms [72]. Motion of the surface atom towards the incoming molecule mcreases the likelihood of (activated) dissociation, while motion away decreases the dissociation probability. For low dissociation probabilities, the net effect is an enliancement of the dissociation by increasing surface temperature, as observed in the system 02/Pt 100]-hex-R0.7° [73]. 

Uthium Mydride. Lithium hydride [7580-67-8] is very stable thermally and melts without decomposition. In the temperature range 600—800°C, the dissociation pressure for hydrogen, Pp, in units of kPa is expressed by... 

Gaseous Hydrogen Chloride. Cast Hon (qv), mild steel, and steel alloys are resistant to attack by dry, pure HCl at ambient conditions and can be used at temperatures up to the dissociation temperature of HCl. The corrosion rate at 300°C is reported to be 0.25 cm/yr and no ignition point has been found for mild steel at 760°C, at which temperature HCl is dissociated to the extent of 0.2%. 

There are three essential factors in the thermal decomposition of limestone (/) the stone must be heated to the dissociation temperature of the carbonates (2) this minimum temperature (but in practice a higher temperature) must be maintained for a certain duration and (J) the carbon dioxide evolved must be removed rapidly. 

Data on chemical properties such as self-dissociation constants for sulfuric and dideuterosulfuric acid (60,65,70,71), as well as an excellent graphical representation of physical property data of 100% H2SO4 (72), are available in the Hterature. Critical temperatures of sulfuric acid solutions are presented in Figure 10 (73). 

Some interesting conclusions can be drawn by plotting log against temperature for thermal dissociation reactions of the type M + CI2 MClj (Mis any given metal). (See Fig. 12.18) . 

For this calculation it is assumed that both the acid and the base are completely dissociated and the activity coefficients of the ions are unity in order to obtain the pH values during the course of the neutralisation of the strong acid and the strong base, or vice versa, at the laboratory temperature. For simplicity of calculation consider the titration of 100 mL of 1M hydrochloric acid with 1M sodium hydroxide solution. The pH of 1M hydrochloric acid is 0. When 50 mL of the 1M base have been added, 50 mL of unneutralised 1M acid will be present in a total volume of 150 mL. 

The base properties of the amine are represented by its basicity constant (basicity dissociation constant, Kh), which identifies the amount of the amine (in moles) that is ionized (i.e., available to raise pH) in liquid water-condensate at any given temperature and pressure. The dissociation reaction for a primary amine is shown in equation 1, and the value of the dissociation constant is shown in equation 2. 

In many CVD reactions for the deposition of nitrides, ammonia (NH3) is used as a source of nitrogen, rather than nitrogen. This is preferable from a thermodynamic standpoint but may present a problem in that any NH3 — either unreacted or present in the regions of furnace where the temperature is below its dissociation temperature— tends to combine with the HCl effluent gas and forms NH4CI, which may clog the exhaust line. 

Reliable information on the thermodynamic stability of group 13/15 adducts is usually obtained by gas phase measurements. However, due to the lability of stibine and bismuthine adducts in the gas phase toward dissociation, temperature-dependent H-NMR studies are also useful for the determination of their dissociation enthalpies in solution [41b], We focussed on analogously substituted adducts t-BusAl—E(f-Pr)3 (E = P 9, As 10, Sb 11, Bi 12) since they have been fully characterized by single crystal X-ray diffraction, allowing comparisons of their thermodynamic stability in solution with structural trends as found in their solid state structures. 

N1 and Zn from a graphite rod were significantly lower than from a tantalum filament, suggesting that these free metal atoms can be liberated by chemical reduction of their respective oxides, rather than by direct thermal dissociation. Findlay et al (19) emphasized the hazards of preatomlzatlon losses of trace met s In electrothermal atomic absorption spectrometry, when the ashing temperature Is permitted to exceed the minimum temperature for vaporization of the analyte. 

By surface science techniques, Mullins and Overbury showed that the presence of reduced ceria might create new active sites for NO dissociation [82], The degree of decomposition is increased and the onset temperature for decomposition is reduced when Rh is supported on reduced ceria (Rh/CeOj compared to Rh on oxidized ceria (Rh/Ce02) NO dissociation being self-inhibiting. 

The phenanthrene system appears to be no more easily cleaved than the naphthalene system however, ethyl anthracene is clearly destabilized significantly more than the other compounds in the table. The large decrease in bond-dissociation energy for the anthracene system is reflected in the increase by three to four orders of magnitude in the rate of scission at conversion temperatures, as shown in the table. 

Also pertinent to Step 1 is the material in Table II, which includes bond dissociation energies and kinetic data at conversion temperatures for a series of C-C bonds. For the purposes of this discussion it can be assumed that substitution of -0- for -CH2-... 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

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