Dissociation thermochemical characteristics

The thermochemical characteristics of l,3,5-trinitro-l,3,5-triazepane, such as energies of dissociation of N-NOz bonds, enthalpies of formation, vaporization, and combustion, as well as enthalpy of formation of amine radicals, have been determined <2004MI92>. The rate constants of initial monomolecular stages of thermal decomposition in the solid phase were measured for its furazano-fused analog 20 <1999RCB1250> and the ratio of the rate constants of decomposition in the melt and solid states, characterizing the reaction retardation in the crystal lattice, was determined. The kinetics of the thermal decomposition of 20 has also been studied <1995MI885>. 

Chemical interference will occur when the analyte element forms with another element, radical, or compound a new compound in the condensed phase and this new compound possesses different thermochemical characteristics. The interference becomes greater with increasing difference in the dissociation temperatures of the original and new compounds. Dissociation is dependent on the flame temperature, the ratio of oxidant/fuel gas, the concentration of the analyte element, the efficiency of the nebulizer, and the measurement height in the flame. 

Mass spectrometry is a unique method that allows study of the reactivity of isolated metal-containing ions in the gas phase in the absence of solvent. A number of fundamental thermochemical characteristics of organometallic molecules and ions, such as ionization energies, proton affinities, electron affinities and metal-ligand bond dissociation energies, can be determined from mass spectrometry experiments. 

It should also be noted that significant progress has been made in the measuring of thermochemical parameters of organozinc complexes. Ionization energies were measured and the dissociation characteristics of ions were determined. The experimental results for gaseous Zn-containing ions were supported by quantum-chemical calculations. 

C-C bond dissociation energies are not the only molecular properties affected by electron transfer. In addition, radical cations exhibit a number of unique characteristics flexible structures [23], a low sensitivity towards steric effects [24], low activation barriers for inter- and intramolecular reactions [25-28], high acidities [29-32] and the inversion of the thermochemical stability order for certain tautomeric systems. Examples in the recent literature demonstrate that it is worthwhile thinking about how the changed molecular properties can be used for the design of new reactions that complement the thermal and photochemical reactivity patterns [26,33-35]. 

Energy characteristics of atoms also define, to a large extent, the strengths of their bonds in molecules, polyatomic ions and radicals. The work required to disrupt a chemical bond, e.g. to separate chemically bonded atoms from the equilibrium distance to a practically infinite one (in the ground state) is called bond energy Eb). In case of the A2 and AX molecules, Eb is equal to the dissociation energy of the molecule (De) which can be determined by thermochemical, calorimetric, kinetic, mass-spectroscopic and molecular spectroscopic techniques. By definition, De characterizes atoms in molecules at the equilibrium state with zero-point energy,... 

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