Disproportionation energies

Dithiazolyl radicals have also attracted considerable attention recently as potential molecular conductors (Section 11.3.6). The advantage of these systems over 1,2,3,5-dithiadiazolyls lies in their relatively low disproportionation energies (Section 11.3.1). 

An intrinsic requirement in the design of neutral radical conductors is a low disproportionation energy for reaction 11.5. Electrochemical investigations of the redox behaviour of 1,2,3,5-dithia and... 

Polymer "moiety"-polymer "moiety" reactions. Chemical groups formed on the backbone of polymer chains such as peroxy radicals, hydroperoxides, ketones, etc. can undergo bimolecular reactions such as disproportionation, energy transfer, etc. The effect of the polymeric medium apparently is to reduce the bimolecular rates by a factor of about 10 4 relative to fluid solution rates, due to the reduced mobility of both reactants. 

Ionization Energy, Electron Afeinity, and Disproportionation Energy... 

If Equation 2.35 is subtracted from Equation 2.34, we obtain the disproportionation energy U ... 

In a molecule as well as in solids, the thermodynamic disproportionation energy is an adiabatic energy difference, meaning that the equilibrium distauces for the nuclei have been used in the definition. When one electron is moved from one site to the next, the equilibrium distances change. Hubbard U, on the other hand, refers to constant positions of the nuclei. 

In the following, U will be frequently used to denote the disproportionation energy. 

Table 2.2 Calculated (BP86/TZVPP) geometrical parameters, M-M bond dissociation energies (BDEs), and disproportionation energies for the group 2 metal(l) dimers, PhMMPh (M = Be-Ba).

Bilbrey JA, Sontag SK, Huddleston NE, Allen WD, Locklin J (2012) On the role of disproportionation energy in Kumada catalyst-transfer polycondensation. ACS Macro Lett 1 995-1000... 

MgCl(s), however, is not energetically stable with respect to disproportionation. The following energy cycle enables the enthalpy of disproportionation to be calculated, i.e. 

Significant vapor pressure of aluminum monofluoride [13595-82-9], AIF, has been observed when aluminum trifluoride [7784-18-1] is heated in the presence of reducing agents such as aluminum or magnesium metal, or is in contact with the cathode in the electrolysis of fused salt mixtures. AIF disproportionates into AIF. and aluminum at lower temperatures. The heat of formation at 25°C is —264 kJ/mol(—63.1 kcal/mol) and the free energy of formation is —290 kJ/mol(—69.3 kcal/mol) (1). Aluminum difluoride [13569-23-8] h.3.s been detected in the high temperature equihbrium between aluminum and its fluorides (2). 

In the absence of air, TEE disproportionates violently to give carbon and carbon tetrafluoride the same amount of energy is generated as in black powder explosions. This type of decomposition is initiated thermally and equipment hot spots must be avoided. The flammability limits of TEE are 14—43% it bums when mixed with air and forms explosive mixtures with air and oxygen. It can be stored in steel cylinders under controlled conditions inhibited with a suitable stabilizer. The oxygen content of the vapor phase should not exceed 10 ppm. Although TEE is nontoxic, it may be contaminated by highly toxic fluorocarbon compounds. 

Such breakers are normally produced for use on an LT system only. At higher voltages, while interrupting heavy currents (such as on a fault) the arc energy may be so high that a disproportionate size of arc chutes may be required to arrest and extinguish the arc, leading to disproportionate size of ACB. 

It is noteworthy that only in the case of dehydroquinolizidine derivatives does monomethylation produce the N-alkylated product. The formation of dialkylated products can be explained by a disproportionation reaction of the monoalkylated immonium salt caused by either the basicity of the starting enamine or some base added to the reaction mixture (most often potassium carbonate) and subsequent alkylation of the monoalkylated enamine. Reinecke and Kray 113) try to explain the different behavior of zJ -dehydroquinolizidine and zJ -dehydroquinolizidine derivatives by the difference in energies of N- and C-alkylation transition states because of the presence of I strain. 

Anhydrous NaC102 crystallizes from aqueous solutions above 37.4° but below this temperature the trihydrate is obtained. The commercial product contains about 80% NaC102. The anhydrous salt forms colourless deliquescent crystals which decompose when heated to 175-200° the reaction is predominantly a disproportionation to C103 and Cl but about 5% of molecular O2 is also released (based on the C102 consumed). Neutral and alkaline aqueous solutions of NaC102 are stable at room temperature (despite their thermodynamic instability towards disproportionation as evidenced by the reduction potentials on p. 854). This is a kinetic activation-energy effect and, when the solutions are heated near to boiling, slow disproportionation occurs ... 

In general, the activation energies for both cationic and anionic polymerization are small. For this reason, low-temperature conditions are normally used to reduce side reactions. Low temperatures also minimize chain transfer reactions. These reactions produce low-molecular weight polymers by disproportionation of the propagating polymer ... 

With reference to rule (3) (Sec. 7.1.3) regarding metal atom mobility, we note that the Gibbs free energies of formation (AG( ) at 298 K for LaNi s and for LaH2 are about -67 and -171 kJ mol-1 respectively. Thus the following disproportionation reaction is highly favored [29] ... 

Even though the absolute rate constant for reactions between propagating species may be determined largely by diffusion, this does not mean that there is no specificity in the termination process or that the activation energies for combination and disproportionation are zero or the same. It simply means that this chemistry is not involved in the rate-determining step of the termination process. 

The result indicates that the activation energy for combination is higher than that for disproportionation by ca 10 kJ mol"1. A similar inverse temperature dependence is seen for other small radicals (Section 2.5). However, markedly different behavior is reported for polymeric radicals (Section 5.2.2.2.1). 

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