Stability AUTHOR INDEX

It was shown by the above authors that nitrogen content of nitric esters such as NG or NC cannot be determined by the nitrometer method, if stabilizers such as centralite are present, because centralite absorbs some nitrogen oxides thus giving a low result for N. The difference between the nitrometer N content of NG in absence of a stabilizer and N content of NG in presence of a stabilizer may be taken as an index of stabilizing action of the stabilizer the bigger the difference, the better the stabilizer. This difference is called indice nitrometrique... 

The most extensive study of the structure of 41 was reported recently by Schleyer, Otto, Cremer and coworkers. As has been described for the homotropenylium cation, their approach involved high-level calculations [MP4(SDQ)/6-31G(d) and IGLO]. These authors concluded that 41 is homoaromatic with a bent structure, relatively short C(l)-C(3) distance (1.737 A), a considerable 1-3 interaction index and nearly equal charges on C(l), C(2) and C(3), the basal ring carbons. The calculated chemical shifts and barrier of inversion of 41 agreed well with those observed by Olah and colleagues. Various estimates of the stabilization energy of 41 were made. 

A comment was presented that an increase in the water content of the oil improves its stability. Another comment was made on the correlation of viscosity and the stability index. More testing and further development of the stability test are needed. The stability index should not be the only measure of the storage stability of oil. Another simple test method may be necessary, The authors wish to bring out that, in some cases, the instructions had not been delivered to technicians, which has lead to erroneous results. Hence, the stability results will be re checked. 

The pharmaceutical industry has been required by regulatory authorities to take a strong interest in polymorphism and solvatomorphism once it was realized that the nature of the structure adopted by a given compound upon crystallization would then exert a profound effect on the solid-state properties of that system. For a given material, the heat capacity, conductivity, volume, density, viscosity, surface tension, diffusivity, crystal hardness, crystal shape and color, refractive index, electrolytic conductivity, melting or sublimation properties, latent heat of fusion, heat of solution, solubility, dissolution rate, enthalpy of transitions, phase diagrams, stability, hygroscopicity, and rates of reactions, were all affected by the nature of the crystal structure. 

Fig. 10 Increase in carbonyl index during aging in air at 80 °C for film-blown PE un-stabilized (A) (PE), containing a-tocopherol (PE-toc), and containing Irganox 1076 (PE-Irgl076), measured by FTIR in ATR mode. owned by the authors...

Fig. 11 Carbonyl index (A) (determined by ATR FTIR) and emitted amount of propanoic acid ( ) (extracted by HS-SPME and identified by GC-MS) in un-stabilized PE (PE-ref) and in PE materials containing a-tocopherol PE-toc, PE-core/toc and PE-EAA/toc, during aging in air at 80 °C. The authors have the right to republish [45]...

Note of the author. Data in the table can describe plastics stabilized with different amounts of antioxidants and cannot be taken as the thermostability index for pure plastics. 

Zahradnlk et al.160 have combined a set of parameters which may be regarded as aromaticity indices into the stability index. The approach is more comprehensive than that of Balaban, but as the authors point out it is obviously difficult to assess the relative importance of the selected indices. Those included are the specific delocalization energy DE,P34 (Section II, A,3,a) related to the extent of -electron delocalization, Aq the difference between the maximum and minimum ir-electron density in the molecule (related to the reactivity toward nucleophilic and electrophilic reagents see the preceding section), the free valence F (related to radical reactivity) and the radical super-delocalizability ST (related to radical reactivity, oxidizability, and reducibility). 

Many authors have concluded that the conjugated diene method might be used as an index of stability of lipids in place of, or in addition to PV. It is faster than iodometric PV determination, much simpler, does not depend on chemical reactions or color development, and requires a smaller sample size. However, the presence of compounds absorbing in the region of the conjugated diene formation may interfere with such determinations. It has been proposed that interference in complex systems can be minimized or eliminated by derivative spectroscopy, using photodiode detection of spectra and computer analysis of the data. ... 

Chermahini et al. (2007JMST(822)33) also studied substituent effects on the aromaticity (expressed by HOMA and NICS indices) of anionic and protonated forms of C5-X tetrazole derivatives (with X = NH2, OH, OMe, SMes, H, Me, F, Cl, BH2, CF3, CN, NO, and NO2). They have shown that the stability order of protonated forms is related to the nature of the substituent. For electron-withdrawing substituents, the stability follows the sequence 1,3-H > 1,4-H > 2,3-H > 1,2-H, but in the case of electron-donating groups the order of the stabihty changes to 1,4-H > 1,3-H > 1,2-H > 2,3-H. NICS(O) values suggest that the anionic forms of tetrazoles are less aromatic than IH- tautomers, whereas the obtained NICS(l) and HOMA values indicate that the aromaticity of anionic forms lies between those found for IH- and 2H- tautomeric forms. In the case of protonated tetrazole derivatives, the most aromatic are the 2,3-H forms, whereas 1,4-H tautomers are the least aromatic. Based on the HOMA index analysis the authors concluded that the aromaticity of protonated systems can be related to the nature of the substituent. However, a closer look on their results suggests that the Tt-electron delocalization of all the studied protonated systems hardly depends on the nature of the substituent at the position C5. 

---