Elimination reactions 378 INDEX

A number of runaway reaction incidents which have involved the formation of polymeric species differ from usual polymerisation reactions of monomers in that elimination reactions of various types have been involved. Individually indexed examples are ... 

A methodology that can classify reactions by using similarity measures has recently been introduced and has now been extended to include a steric similarity index. Both substitution and elimination reactions are included. 

Finally, the global and local electrophilicity indexes may be also used to describe the nucleofugality of classical leaving groups in organic chemistry. This potential application incorporates the important families of nucleophilic substitution and elimination reactions. This study is however a bit more complex than the cases presented in this review, because the systematization of nucleofugality within an absolute scale requires an important number of requisites that must be fulfilled, most of them regarding the different reaction mechanisms involved in these complexe reactions. 

A theoretical study of the thermal decomposition kinetics of ethyl fluoride 1,1-difluoroethane 1,1,1-trifluoroethane and 1,1,2,2-tetrafluoroethane has been carried out at the B3LYP/6-31-H-G, B3PW91/6-31-H-G, and MP2/6-31-h-hG levels of theory. The calculated data demonstrate that in the HF elimination reaction of the compounds studied, the polarization of the C(l)-F(3) bond is rate determining. Analysis of bond order, charges, bond indexes, and synchronicity parameters suggests that HF elimination occurs through a concerted and asynchronous four-membered cyclic TS type of mechanism. 

In Table 1 the experimental data (weight average of molar mass, polydispersity index, decomposition temperature and heat of decompositioiO of polymers with varius add groups — OR (see equ.l) and different stereochemistry are listed. It can be seen, that the decomposition temperature decreases from ca. 390 °C for poly(emfo,endo-2,3-diacetoxy-5-norbomene), polymer 1 b, down to ca. 270 C for poly(e >,exo 5-norbomene-23-bis(methylcarbonate)), pofymer 3 a. As erqpected, the polymers from the exo,eco-isomers decomposed at lower temperatures as the endo,endo- sova.cK because the thermal elimination reaction is a typical syn-elimination ... 

Depolymerization, elimination, and statistical chain-scission reactions can be used for polymer analysis. When the monomer is the main degradation product obtained, it can easily be identified by boiling point and refractive index. 

Absorption of theophylline from the gastrointestinal tract is usually rapid and complete. Some 90% is metabolised by the liver and there is evidence that the process is saturable at therapeutic doses. The tis 8 h, with substantial variation, and it is prolonged in patients with severe cardiopulmonary disease and cirrhosis. Obesity and prematurity are associated with reduced rates of elimination, whereas tobacco smoking enhances theophylline clearance by inducing hepatic P450 enzymes. Because of these pharmacokinetic factors and low therapeutic index, monitoring of the plasma theophylline concentration is necessary to optimise its therapeutic effect and minimise the risk of adverse reactions the optimum concentration range is 10-20 mg/1 (55-110 mmol/1). 

---