Kinetic investigation of the reactions of S-4-nitrophenyl 4-substituted thiobenzoates with secondary alicyclic amines in aqueous ethanol

The reactions of S-4-nitrophenyl 4-X-substituted thiobenzoates (X = H, Cl, and NO(2): 1, 2, and 3, respectively) with a series of secondary alicyclic amines (SAA) were subjected to a kinetic investigation in 44 wt % ethanol-water, at 25.0 degrees C and an ionic strength of 0.2 M (KCl). The reactions were followed spectrophotometrically by monitoring the release of 4-nitrobenzenethiolate anion at 420-425 nm. Under excess amine, pseudo-first-order rate constants (k(obsd)) are obtained for all reactions. The plots of k(obsd) vs [SAA] at constant pH are linear with the slope (k(N)) independent of pH. The statistically corrected Br?nsted-type plots (log k(N)/q vs pK(a) + log p/q) for the reactions of 1 and 2 are nonlinear with slopes at high pK(a), beta(1) = 0.27 and 0.10, respectively, and slopes at low pK(a), beta(2) = 0.86 and 0.84, respectively. The Br?nsted curvature is centered at pK(a) (pK(a)(0)) 10.0 and 10.4, respectively. The reactions of SAA with 3 exhibit a linear Br?nsted-type plot of slope 0.81. These results are consistent with a stepwise mechanism, through a zwitterionic tetrahedral intermediate (T(+/-)). For the reactions of 1 and 2, there is a change in rate-determining step with amine basicity, from T(+/-) breakdown to products at low pK(a), to T(+/-) formation at high pK(a). For the reactions of 3, breakdown to products of T(+/-) is rate limiting for all the SAA series (pK(a)(0) > 11). The increasing pK(a)(0) value as the substituent in the acyl group becomes more electron withdrawing is attributed to an increasing nucleofugality of SAA from T(+/-). The greater pK(a)(0) value for the reactions of SAA with 1, relative to that found in the pyridinolysis of 2,4-dinitrophenyl benzoate (pK(a)(0) = 9.5), is explained by the greater nucleofugality from T(+/-) of the former amines, compared to isobasic pyridines, and the greater leaving ability from T(+/-) of 2,4-dinitrophenoxide relative to 4-nitrobenzenethiolate.     

Kinetics and mechanism of the reactions of S-2,4-dinitrophenyl 4-substituted thiobenzoates with secondary alicyclic amines

[reaction: see text] The title reactions, in 44 wt % ethanol-water at 25.0 degrees C, exhibit slightly curved Br?nsted-type plots (log kN versus pKa of amines) with slopes beta1 = 0.1-0.44 (at high pKa) and beta2 ca. 0.7 (at low pKa). The magnitude of some of these slopes, together with the fact that the curvature center (pKa(0) = 9.5-10.8) does not change with the electronic effects of the benzoyl substituent, suggests that these reactions are not stepwise, but concerted.     

Antiaromaticity in relation to 1,3,5,7-cyclooctatetraene structures

An isodesmic energy analysis has been carried out at the MP 2/6–31G *//HF /3–21G level for the nonplanar ground state ( 1 ) of 1,3,5,7-cyclooctateraene and for two planar forms, one having complete π delocalization ( 2 ) and the other having alternating single and double bonds ( 3 ). 1 is found to have a considerable degree of stabilization, which is attributed to limited π delocalization. The polyene 3 is the more stable of the two planar forms; it is a transition state in the inversion between two possible nonplanar structures. 2 is found to be a triplet at the Hartree–Fock level and is a critical point on an alternate pathway between the two possible arrangements of alternating single and double bonds in 3 . Both 2 and 3 have negative isodesmic energies, indicating the presence of stabilizing factors. Our results for 3 show that an “antiaromatic” system need not necessarily show a net destabilization. © 1994 John Wiley & Sons, Inc.     

Conlometric determination of weak bases applying bismuth electrode pair for the end-point detection

Tertiäre Amine und Salze organischer Säuren werden in Acetanhydrid mit 5% Essigsäure durch anodische Proton-Erzeugung auf Platin in Gegenwart von Hydrochinon mit Hilfe der biamperometrischen Endpunkttechnik mit einem Wismutelektrodenpaar quantitativ bestimmt. Mengen von 0,5–0,9 mg wurden mit einer mittleren Abweichung von <1% analysiert. Die Ergebnisse stimmten zufriedenstellend mit denen aus thermometrischen und photometrischen Titrationen überein.Summary Tertiary amines and salts of organic acids have been quantitatively determined in acetic anhydride with 5% of acetic acid by means of anodic generation of protons on platinum in the presence of hydroquinone, applying a biamperometric end-point detection using an indicating system of bismuth electrodes. Amounts of 0.5–0.9 mg have been analysed with average deviations of <1%. Good agreement was obtained with the results of thermometric and photometric titrations.

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Coulometrische Bestimmung von schwachen Basen unter Anwendung eines Wismut-Elektrodenpaars als Indicatorsystem

     

Autoxidation kinetics of atactic polypropylene in bulk

The kinetics of the reaction between atactic polypropylene (APP) and oxygen in bulk at temperatures ranging from 170 to 210°C and oxygen partial pressures from 160 to 760 torr have been studied by thermal differential analysis. The reaction takes place in two successive steps, both giving hydroperoxide groups as product. Partial reaction orders with respect to APP and oxygen for the first step, which corresponds to the uncatalyzed attack of a C? H tertiary bond to give a hydroperoxide, are one and two, respectively. In the second step, interpreted as another attack on a tertiary C? H by oxygen, catalyzed by a neighboring hydroperoxide group, reaction orders are one and one-half for APP and oxygen, respectively. Activation parameters have been determined and a reaction sequence is proposed. Hydroperoxidated APP subsequently decomposes via a zero-order process giving methylketone groups as its main product. An interpretation of this process is also given.     

Rare earth metal complexes with 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione. An example of anhydrous rare earth β-diketonates

Summary The interaction of non-anhydrous solutions of the ligand 1,3-bis-(2-hydroxyphenyl)-1,3-propanedione (bhppH₃) with hydrated rare earth chlorides resulted in the formation of anhydrous, non-solvated, complexes M(bhppH₂)₃ (M=Y, La, Nd, Pr, Sm or Yb). The complexes have been characterized by elemental analysis, t.g., i.r. and¹H n.m.r. spectroscopy. The evidence suggests that the coordination is through the -diketone site.     

Synthesis,Structure and Reactivity of [1, 2‐Bis(diphenylphosphinite)ethane]bromotricarbonylmanganese(I) with Reactions of Phosphites,Phosphonites. and Phosphinites

The manganese carbonyl complex [MnBr(CO)₃ L ] ( 1 ), where L = Ph₂POCH₂CH₂OPPh₂, was prepared by reacting [MnBr(CO)₅] with the bidentate ligand 1, 2‐Bis(diphenylphosphinite)ethane. From this compound and the appropriate phosphite, phosphinite or phosphonite ligands were synthesized the complexes [MnBr(CO)₂ LL ′], where L ′ = P(OMe)₃ ( 2 ) or P(OEt)₃ ( 3 ) and [MnBr(CO)₃ L ′₂], where L ′ =PPh(OEt)₂ ( 4 ) or PPh₂(OEt) ( 5 ). The obtained compounds have been characterized by elemental analysis, mass spectrometry, IR and NMR (¹H, ¹³C and ³¹P) spectroscopies and X‐ray diffractometry for the complexes 1 , 4 and 5 .     

Double exchange in polynuclear mixed-valence clusters. 1. General solution of the electronic problem

The problem of calculating the electronic energy spectra of mixed-valence clusters with one “extra” electron (dⁿ-dⁿ...dⁿ⁺¹) or hole (dⁿ⁺¹-dⁿ⁺¹...dⁿ) delocalized in the paramagnetic cores of transition metals is solved. Unlike the available particular solutions, which are restricted to small numbers of ions and electrons, the solution proposed in this work is general and is suitable for many-electron systems of arbitrary numbers of nuclei and arbitrary symmetries. The new microscopic approach to the double exchange problem is based on the combination of the sequential (“chain”) scheme of spin coupling and angular momentum method. In terms of this approach, an analytical dependence of the matrix elements of the double exchange, Heisenberg exchange, and vibronic interaction on all spin quantum numbers is obtained. The final equations contain only the 6j symbols and are free of the higher-order nj symbols, which obstructed the solution of the double exchange problem in previous works. Valencia University, Spain. Bordeaux University, France. Moldova State University. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 805–815, September–October, 1996. Translated by I. Izvekova     

Role of Hartree-Fock and Kohn-Sham orbitals in the basis set superposition error for systems linked by hydrogen bonds

In this work the effect of the basis set superposition error (BSSE) is explored with the counterpoise method on the occupied and unoccupied Hartree-Fock (HF) and Kohn-Sham (KS) orbitals. Three different systems linked by hydrogen bonds, H(2)O...FH, H(2)O...H(2)O, and H(2)O...CFH(3), were studied by using the basis set families cc-pVXZ and aug-cc-pVXZ (X = D, T, Q). The basis sets were tested with the HF method and two approximations for the exchange-correlation functional of KS: a generalized gradient approximation and a hybrid approach. In addition to these methods, the second-order M?ller-Plesset perturbation theory, MP2, was considered. It was found that the presence of the "ghost" basis set affects the orbitals in two ways: (1) The occupied KS orbitals are more sensitive to the presence of this "ghost" basis set than the occupied HF orbitals. For this reason the BSSE observed in HF is less than that obtained with KS. (2) The unoccupied HF orbitals are more sensitive to the presence of the "ghost" basis set than their corresponding occupied orbitals. Because the MP2 method uses both, occupied and unoccupied HF orbitals, to compute the total energy, the contribution of the BSSE is bigger than that obtained with HF or KS methodologies.