NOPR Collection:

Symmetry consideration for the interpretation of isomeric product distribution in spontaneous aquation of octahedral cobalt(III) complexes

2017-05-23T07:05:35Z

Title: Symmetry consideration for the interpretation of isomeric product distribution in spontaneous aquation of octahedral cobalt(III) complexes Authors: Pradhan, Guru C Abstract: The stereochemical changes involved in the aquation of octahedral cobalt(III) complexes [(N₄Co(A)X]ⁿ⁺, where X is a leaving group, are related to the stereomobility of the transition state and/or the Intermediate generated in the dissociative mode of reaction of the parent substrate. An attempt is made to explain the relative isomer distribution in the products of spontaneous aquation of such complexes applying a recently developed symmetry selection rule. Page(s): 301-307

Methyl nitrene: Thermochemistry and kinetics of its rearrangement to methyleneimine

2017-05-23T07:04:05Z

Title: Methyl nitrene: Thermochemistry and kinetics of its rearrangement to methyleneimine Authors: Kakkar, Rita; Walia, Vibha Abstract: The thermal unimolecular isomerisation of methylnitrene to methyleneimine has been studied, and the macroscopic thermodynamic and kinetic properties have been calculated using the vibrational frequencies and rotational constants evaluated theoretically. The high pressure rate constants have been calculated and the fall-off behaviour has been studied using the calculated reactant and transition state properties. Kinetic isotope effects on the reaction have also been studied. The effects of fluorine substitution on the thermochemical and kinetic parameters have also been investigated. Page(s): 308-312

Effect of temperature on hydrogen isotope effects in dehydration of ion-exchange resins: Alkali metal ionic (Li⁺, K⁺ and Cs⁺) forms of Dowex-50W resins

2017-05-23T07:02:57Z

Title: Effect of temperature on hydrogen isotope effects in dehydration of ion-exchange resins: Alkali metal ionic (Li⁺, K⁺ and Cs⁺) forms of Dowex-50W resins Authors: Inamdar, Neeta C; Sarpal, S K; Gupta, A R Abstract: Hydrogen isotope effects in dehydration of alkali metal ionic (Li⁺, K⁺ and Cs⁺) forms of Dowex-50W resins (with 2, 4, 8 and 12% divinylbenzene content), having n_w, (number of moles of water per equivalent of resin) values of ~2 to ~27, have been determined at 303, 318 and 333K using a Rayleigh distillation type technique. For very low n_w, values, the observed single stage separation factor, α_obs" for all the systems is independent of temperature and has a constant value of ~1.025 ± 0.004, which is much lower than α_w, the single stage separation factor for pure water distillation at that temperature. In the case of Li⁺ resins at all temperatures and K⁺ and Cs⁺ resins at higher temperatures only, the α_obs varies with n_w as follows: as n_w, -value increases, α_obs increases gradually, reaches a maximum value, α_max (at n_max which is greater than a_w. At still higher n_w, -values the α_obs decreases gradually and finally approaches the α_w. In these systems where a maximum is observed in the ε_obs[= α_obs - 1] versus n_w, plots, the data have been analysed in terms of the three-water sub-system-model for cation hydration and the ε₁, ε₂ and ε₃ representing the separation factors for the water molecules in the primary shell, the secondary shell and the bulk water, respectively have been obtained. Analysis of the results for different temperatures shows that ε₁, and ε₂ originating from electrostatic interaction, are temperature independent. The fact that ε₃,= ε_w (within the experimental error), shows that the effect of cationic charge does not extend beyond the second layer of water molecules. At lower temperature (303K), ε_obs versus n_w; plots for K⁺and Cs⁺ resins do not exhibit a maximum and ε_obs approaches ε_w at high n_w , values. Further, ε₂ (353 or 303K) < ε_w(303K) for these systems. These data show that water structure is preferentially formed at high n_w., values at the expense of hydration shells, i.e., the hydration shells are destroyed by the more stable water structure at these temperatures. For any cationic form of the resin, the sharpness in the maximum of ε_obs versus n_w, curve increases with increase in temperature, implying that with increasing temperature the bulk water structure is destroyed more rapidly than the hydration shell water structure. These observations are in consonance with the views reported in literature (see ref. 13) on electrolyte solutions. Page(s): 313-321

Changes in thermodynamic parameters in the exchange of alkaline earth metals with sodium ions in Dowex-50Wx 8 and Amberlyst-15 resins in aqueous medium

2017-05-23T06:37:45Z

Title: Changes in thermodynamic parameters in the exchange of alkaline earth metals with sodium ions in Dowex-50Wx 8 and Amberlyst-15 resins in aqueous medium Authors: Toteja, R S D; Jangida, B L; Sundaresan, M Abstract: Standard free energy, ∆G°, enthalpy, ∆H°and entropy, ∆S°, changes have been evaluated for Mg²⁺/Na⁺ , Ca²⁺/Na⁺ +, Sr²⁺INa⁺, Ba²⁺INa⁺ exchange systems on strong polystyrenesulfonic (PSS) acid type cation exchange resins, Dowex-50WX8 and Amberlyst-15 (macroreticular) in dilute aqueous solutions from equilibrium ionic distribution and heat of exchange measurements calorimetrically at 298K. The alkaline earth metals are preferred by both the resins and the preference increases from magnesium through barium. The selectivity is lower for all the metals on Amberlyst-15 resin. The exchanges take place with absorption of heat. The endothermicity is more on Amberlyst-15 and it decreases with increasing size of the metal ion on both the exchangers. The uptake of divalent ions is governed by increase in entropy. The difference in entropies of hydration of alkaline earth metal and sodium ions is considered to be a major factor responsible for increase in standard entropy. The lower selectivity of alkaline earth metals on Amberlyst-15 is attributed to decrease in the hydration numbers of the cations in the resin since it imbibes more water than Dowex-50WX8. Page(s): 322-327

NOPR Collection:

Symmetry consideration for the interpretation of isomeric product distribution in spontaneous aquation of octahedral cobalt(III) complexes

Methyl nitrene: Thermochemistry and kinetics of its rearrangement to methyleneimine

Effect of temperature on hydrogen isotope effects in dehydration of ion-exchange resins: Alkali metal ionic (Li+, K+ and Cs+) forms of Dowex-50W resins

Changes in thermodynamic parameters in the exchange of alkaline earth metals with sodium ions in Dowex-50Wx 8 and Amberlyst-15 resins in aqueous medium

Effect of temperature on hydrogen isotope effects in dehydration of ion-exchange resins: Alkali metal ionic (Li⁺, K⁺ and Cs⁺) forms of Dowex-50W resins