NOPR Collection:

Contrasting isomer stabilities of silaboranes and carboranes : Si2B3H5 and C2B3H5 isomers

1992-09-01T00:00:00Z

Title: Contrasting isomer stabilities of silaboranes and carboranes : Si2B3H5 and C2B3H5 isomers Authors: Jemmis, Eluvathingal D; Subramanian, G Abstract: The relative stabilities of the isomers of closo- Si₂B₃H₅ have been calculated at the MNDO, HF/6- 31G* and MP2/6-3IG* levels. Contrary to the results for the corresponding carborane C₂B₃H₅ reported earlier, Si₂B₃H₅is predicted to be the most stable. The concept of the compatibility of orbitals in overlap is used to rationalize our observation of this reversal of trends in isomer stabilities. Page(s): 645-646

Cyclic conjugation in benzo-annelated polyacenes

1992-09-01T00:00:00Z

Title: Cyclic conjugation in benzo-annelated polyacenes Authors: Gutman, Ivan; Petrovic, Vesna Abstract: Conjugation along a particular ring in a polycyclic conjugated molecule can be measured by means of the effect of the ring on total π-electron energy. Using this approach, we have studied cyclic conjugation in mono-, di-, tri- and tetra-benzo polyacenes. The main conclusion of our research is that the Clar aromatic sextet formulas of the benzo-annelated polyacenes provide a reasonable description of their conjugation modes. A few refinements are, however, possible. The extent of cyclic conjugation is found to be minimal in the central region of the polyacene molecule and it monotonically increases towards its two termini. Geminal annelation has an extra increasing effect on cyclic conjugation. Isoarithmic systems are shown to have practically coinciding conjugation modes. Page(s): 647-650

Hot atom chemistry in oxyanion targets: Part V―Pre-activation heat treatment study of recoil 56Mn in permanganates

1992-09-01T00:00:00Z

Title: Hot atom chemistry in oxyanion targets: Part V―Pre-activation heat treatment study of recoil 56Mn in permanganates Authors: Mishra, Shuddhodan P; Singh, (Miss) Jyoti Abstract: The effect of pre-heat treatment on the fate of ⁵⁶Mn recoil atoms originating from (n, γ) reaction in KMnO₄, Ba(MnO₄)₂ and NH₄MnO₄ targets results in a slight increase in the initial ⁵⁶Mn retention and decrease in the extent of subsequent thermal annealing. Fletcher-Brown model has been utilized to deduce the kinetic behaviour of the annealing phenomenon which consists of two apparent first order processes for both the pre-heated and untreated permanganates. The implications of the results are explained on the basis of competitive participation of oxidising/reducing inherent crystal defects. Page(s): 651-657

Effect of 3-fluoro-4-cyano substituted benzoates in the formation of induced smectic phases with N-[4-ethoxybenzylidene]-4'-n-butylaniline

1992-09-01T00:00:00Z

Title: Effect of 3-fluoro-4-cyano substituted benzoates in the formation of induced smectic phases with N-[4-ethoxybenzylidene]-4'-n-butylaniline Authors: Sharma, N K; Charak, Anila; Ostereicher, F Abstract: Diagrams of state of the binary liquid crystalline systems, in which one component is a 4-cyano-3-fluoro substituted benzoates and the other component is N-[4-ethoxybenzylidene]-4'-n-butylaniline, have been investigated. The nematic phase shows uninterrupted miscibility in ali the binary systems. Induced smectic. A phase is observed in all but one diagram of state. The effect of 4-cyano-3-f1uoro substitution on induced phases is discussed on the basis of dipole moments. Page(s): 658-660