Dimers gaseous

Wilson" " measmed the enthalpy of formation of soUd aluminium isopropoxide which was found to be A/7f°[Al(OPr )3]4(s) = 1230.8 kcalmoR. On the basis of this value, the enthalpy of formation of dimeric gaseous isopropoxide was calculated to be A/7f°[Al(OPr )3]2(g) = 584.8 kcalmol. These two factors led to the minimum value of Al-O bridge bond AHaet = -l-31.4kcalmol . ... 

Vilcu and Misdolea [143] applied the significant structure theory and considered dimeric gaseous species too, obtaining acceptable values of the calculated constant volume heat capacity, but not of the constant pressure values. Contrary to these results, the constant pressure heat capacity calculated by Lu et al. [142] agreed with the experimental data, but the estimated critical temperatures were only 49-76 % of the values in Table 3.3, with opposite trends regarding the sizes of the anions. This was remedied by Cheng et al. [144] who applied a version of the significant structure theory to the estimation of thermophysical quantities for the same alkali metal halides as studied by Lu et al. [142] with acceptable success. 

The entropy value of gaseous HCl is a sum of contributions from the various transitions summarized in Table 4. Independent calculations based on the spectroscopic data of H Cl and H Cl separately, show the entropy of HCl at 298 K to be 186.686 and 187.372 J/(mol K) (44.619 and 44.783 cal/(mol K), respectively. The low temperature (rhombic) phase is ferroelectric (6). SoHd hydrogen chloride consists of hydrogen-bonded molecular crystals consisting of zigzag chains having an angle of 93.5° (6). Proton nmr studies at low temperatures have also shown the existence of a dimer (HC1)2 (7). 

For the two most important industrial uses, the gaseous ketene is immediately treated with acetic acid to form acetic anhydride or dimerized to diketene. 

The enU opy of activation may be estimated from experimental data for gaseous molecules, and in the special case of HI formation, which may be regarded as involving the intermediate formation of tire dimer H2I2, using the general empirical relationship... 

These results, together with infrared and electron diffraction studies, indicate that gaseous HF comprises an equilibrium mixture of monomers and cyclic hexamers, though chain dimers may also occur under some conditions of temperature and pressure ... 

Subsequent reactions depend on conditions. Ultraviolet photolysis of isolated molecules in an inert matrix yields the radicals CIO and CIOO. At room temperature, photolysis of diy gaseous CIO2 yields CI2, O2, and some CIO3 which either dimerizes or is further photolysed to CI2 and O2 ... 

Complexes with dithiocarbamates involve linear S-Au-S coordination but are dimeric and the Au-Au distance of 276 pm compared with 288 pm in the metal and 250 pm in gaseous Au2 is indicative of metal-metal bonding. ... 

Free borane (2) exists as gaseous dimer—the diborane BaHg. In addition Lewis acid/Lewis base-complexes, as for example formed in an ethereal solvent, e.g. 4, are commercially available ... 

Effect of molecular diffusion and vapor-phase chemical reactions Liquid metal vapors consist of molecules and gaseous atoms. Working with alkali metals, Ewing et al. (1967) found that the molecules are principally dimers and tetramers. The... 

Instead of forming a cubane or a dimer the X-ray structural analysis of monosodiated di-tert-butylsilandiol reveals a hexagonal prism formed by the sodium and oxygen atoms of six molecules this structural element is stable even in the gaseous state [2]. 

Photoexcitation of an acetylene molecule results in either dimerization or dissociation of the molecule (C2 + H2 or C2H + H). In the mass spectrometer, the major positive ions are C2H2+ (75%) and C2H+ (15%). However, at STP no gaseous products are seen under radiolysis. There are only two major products, benzene and a polymer, cuprene with an empirical formula QJH. The detailed mechanisms are still debatable. However, the following remarks may be made ... 

Broadened band. The Vs (OH) band goes from 30 cm-1 width in the case of gaseous acetic acid monometer, and it increases up to 400 cm-1 for hydrogen-bonded dimers. 

These short Au-Au contacts may be compared with distances of 2.88 A in metallic gold and 2.60 A in gaseous Au2. The term aurophilicity has been coined by H. Schmidbaur to describe the phenomenon [189,194], The interactions can occur as pairs, squares, linear chains or two-dimensional arrays of gold centres. Examples include the association between dimer units in the dithiocarbamates Au(dtc)2 (Figure 4.16) and the ionic tetrahydrothiophen complexes Au(tht)2 AuXJ (X = halogen), where cations and anions stack with Au—Au 2.97-2.98 A (X = I). The interaction is such that Au(S203)2 pair up, despite their charge, with Au-Au 3.24 A in the sodium salt. Likewise in Aupy AuCl, cations pair up at 3.42 A apart [10, 195]. 

Data for the dimerization of gaseous butadiene to vinyl cyclohexene were obtained at 326 C in a constant volume apparatus by Vaughan (JACS 54 3863, 1932), with time in minutes and total pressure 7r in Torr. Find the constants of the rate equation. 

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