Alkenes chemical behaviour

Bonding of the 3jt p(P)-2jt p(C) type is now generally believed to be present in the trivalent phosphorus compounds indicated in Table 6.13. Such compounds have proved invaluable in the synthesis of organophosphorus ring and cage derivatives. It is believed that the chemical behaviour of P=C bonds mimics that of alkenes very closely [15]. 

The chemically activated molecules are fonned by reaction of with the appropriate fliiorinated alkene. In all these cases apparent non-RRKM behaviour was observed. As displayed in figure A3.12.11 the measured imimolecular rate constants are strongly dependent on pressure. The large rate constant at high pressure reflects an mitial excitation of only a fraction of the total number of vibrational modes, i.e. initially the molecule behaves smaller than its total size. However, as the pressure is decreased, there is time for IVR to compete with dissociation and energy is distributed between a larger fraction of the vibrational modes and the rate constant decreases. At low pressures each rate constant approaches the RRKM value. 

It should always be remembered of course, that the NMR spectrum reflects a compound s behaviour in solution. It is quite possible for a compound and a weak acid to crystallise out as a stoichiometric salt and yet in solution, for the compound to give the appearance of a free base. For this reason, care should be taken in attempting to use NMR as a guide to the extent of protonation. If the acid has other protons that can be integrated reliably, e.g., the alkene protons in fumaric or maleic acid, then there should be no problem but if this is not the case, e.g., oxalic acid, then we would council caution Do not be tempted to give an estimate of acid content based on chemical shift. With weak acids, protonation may not occur in a pro rata fashion though it is likely to in the case of strong acids. 

In both the GC-SAFT-VR and SAFT-y approaches, compared in Figure 8.7, the group parameters are determined by fitting to the experimental vapour pressures and saturated-liquid densities of the smaller members of chosen chemical families i.e. alkanes, branched alkanes, 1-alkenes, alkylbenzenes, ketones, alkyl acetates and methyl esters, among others). The predictive capability of the methods is then tested by assessing the description of the fluid phase behaviour of larger molar mass compounds that were not included in the determination of the group parameters. 

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