Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G^*(6D) basis set. Least-squares refinement of a model withC _s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, =119.0±0.2 (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1, 120.7±0.1, and 119.0±0.3, respectively. Important bond distances are r _g(C-C)=1.398±0.003 å andr _g(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is ¦¦=44±4. The equilibrium dihedral angle is calculated to be 41.8 at the HF level and 43.6 at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(C_ortho-C_meta) -r(C_ipso-C_ortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.     

Molecular structure and conformational composition of 1-Chlorobutane, 1-Bromobutane,and 1-Iodobutane as determined by gas-phase electron diffraction and ab initio calculations

Gas-phase electron diffraction (ED), together with ab initio molecular orbital calculations, have been used to determine the structure and conformational composition of 1-chlorobutane, 1-bromobutane, and 1-iodobutane. These molecules may in principle exist as mixtures of five different conformers, but only three or four of these were observed in gas phase at temperatures of the ED experiments, 18C, 18C, and 23C, respectively. The observed conformational compositions (1-chlorobutane, 1-bromobutane, and 1-iodobutane) were AA (13 ± 12%, 21 ± 14%, 19 ± 17%), GA (60±13%, 33±32%, 17±31%), AG (12±16%, 8±12%, <1%), and GG (12 ±16%, 38± 34%, 64±31%). A and G denotesanti andgauche positions for the X-C₁-C₂-C₃ (X=Cl, Br, I), and the C₁-C₂-C₃-C₄ torsion angles. The results for the most important distances (r _g) and angles () from the combined ED/ab initio study for the GA conformer of 1-chlorobutane, with estimated 2 uncertainties, arer(C₁-C₂)=1.519(3)å,r (C₂-C₃)=1.530(3) å,r (C₃-C₄)=1.543(3) å,r (C₁-Cl)=1.800(4) å, <C₁C₂C₃=114.3(6), <C₂C₃C₄=112.0(6), <CCCl=112.3(5). The results for the GA conformer of 1-bromobutane arer (C₁-C₂)=1.513(4) å,r (C₂-C₃)=1.526(4) å,r (C₃-C₄)=1.540(4) å,r(C₁-Br)=1.959(8) å, <C₁C₂C₃=115.3(11), <C₂C₃C₄=112.8(11),<CCBr=112.1(14). The results for 1-chlorobutane and 1-bromobutane are compared with those from earlier electron diffraction investigations. The results for the GA conformer of 1-iodobutane arer (C₁-C₂)=1.506(5) å,r (C₂-C₃)=1.518(5) å,r (C₃-C₄)=1.535(5) å,r (C₁-I)=2.133(11) å, <C₁C₂C₃=116.8(15), <C₂C₃C₄=115.3(15), <CCI=110.2(14). Differences in length between the different C-H bonds in each molecule, between the different C-C bonds, between the different CCH angles, and between the different CCC angles were kept constant at the values obtained from the ab initio calculations.     

Structure and conformation of 1-Bromopropane: A gas-phase electron-diffraction investigation using microwave-spectroscopy data and results from ab initio calculations as constraints

1-Bromopropane has been studied by gas-phase electron diffraction (ED) at 24C. Earlier published values for rotational constants from microwave spectroscopy (MW), together with results from ab initio molecular-orbital calculations, have been included in the ED analysis. Two conformers with C-C-C-Br torsion angles of 180 (anti) or 66.0(17) (gauche) have been observed. The results obtained for the bond distances (r _g) and valence angles () from this combined ED/MW analysis, with the ab initio results used as constraints are r (C-H)=1.114(9) å,r(C₁-C₂)=1.521(5) å,r(C₂-C₃)=1.535(5) å,r (C₁-Br)=1.962(6) å, <(C-C-C)anti,=110.0(11), <(C-C-C)gauche=113.3(11), < (C-C-Br)anti=111.1(6), < (C-C-Br)gauche=112.1(6), <C₂-C₁-H=112.1 (ab initio value), <C₂-C₃-H=111.4 (ab initio value), <H-C₂-H=107.0 (ab initio value). Error limits are given as 2, where (standard deviation) includes estimates of uncertainties in voltage/height measurements and correlation in the experimental data. The observed amountof gauche conformer was 64(14)%. Using the entropy difference between conformers obtained in the ab initio calculations, this composition corresponds to an energy difference of E=E _anti —E _gauche=0.03(36) kcal/mol. The results are compared with those earlier obtained for other 1-halopropanes.     

Differential scanning calorimetric study of phase changes in poly(ethylene glycol) dodecyl ether-water systems

Phase changes in binary systems of poly(ethylene glycol) dodecyl ethers, C₁₂H₂₅(OC₂H₄)_xOH (x=5, 6 and 8) with water have been studied between –40 to 100 C by differential scanning calorimetry. A number of transitions, including the liquidliquid phase separation, were seen and the transition temperatures and enthalpy changes were determined. The observed temperatures were generally in good agreement with reported phase diagrams. In the C₁₂E₅ system, three of the four three-phase lines were seen and a more complete phase diagram is suggested for the water-rich part of the system. Most of the phase changes seen above 0 C are accompanied by small endothermic enthalpy changes of 0.7 to 0.9 kJ (mol C₁₂E_x)^–1, independent of system studied, type of transition and transition temperature. Water-rich solutions and liquid crystalline phases separate upon freezing into ice and crystals of hydrated amphiphile. Eutectics are developed at the following temperatures and compositions: C₁₂E₅ –3.0 C and 54 wt % C₁₂E₅; Q₂E₆ –4.5 C and 54 wt % C₁₂E₆, C₁₂E₈ –3.8 C and 49 wt % C₁₂E₈.     

Metal ion catalysed aquation of carboxylatoamine cobalt(III) complexes. Kinetics of copper(II) catalysed aquation ofcis(diformato)bis(ethylenediamine)cobalt(III) ion

Summary The aquation ofcis-[(en)₂Co(CO₂H)₂]⁺ tocis-[(en)₂Co(OH₂)(CO₂H)]²⁺ is catalysed by Cu²⁺ and the rate equation, –d[complex]_t/dt=(k_Cu[Cu²⁺]+k_H [H⁺]) [complex)_T is valid at [Cu²⁺]_T=0.01–0.1, I=0.5 and [HClO₄]=0.005 mol dm^–3. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu²⁺ and H⁺-catalysed paths are: k_H(35°C)=(2.44±0.09)×10^–2 dm³ mol^–1 s^–1, H=83±13 kJ mol^–1, S=–8±42 JK^–1 mol^–1, k _Cu (35°C)=(3.30±0.09)×10^–3 dm³ mol^–1 s^–1, H=73.2±6.1 kJ mol^–1, S=–55±20 JK^–1 mol^–1. The formate-bridged innersphere binuclear complex,cis-[(en)₂Co{(O₂CH)₂Cu}]³⁺ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H⁺-bridged species presumed to be present in the acidcatalysed path.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

Diffusion of linear aliphatic esters in polyethylene as a function of chain length of the esters,pressure and temperature

Diffusion of linear aliphatic mono- and diesters (C _N ) havingN main chain atoms (N=13–68) in bulk medium-density polyethylene (MDPE) has been studied under hydrostatic pressures up to 2500 bar at temperatures between 60°C and 125°C. Three triglycerides, phenyl stearate, and p-aminoazobenzene (pAAB, 80°C) as the diffusants and low-density (LDPE) and high-density (HDPE) polyethylenes as polyethylene substrate were used for comparison. Diffusion coefficientD was determined from concentration distribution of the diffusants through stacked PE sheets as substrate. Regarding the linear esters at 90°C, the relationshipD N holds at constant pressures. Under the atmospheric pressure, became –2.10 in accordance with de Gennes's proposal (1971)D N ^–2 as well as with the experimental results reported by Klein and Briscoe (1979) forN larger than 30.D's for the glycerides deviate from the relationshipD N ^–2 toward the smaller values by comparison at the sameN. The exponent is pressure-dependent. It decreases with increasing pressure according to =–2.10–0.000942P, whereP is measured by the unit of bar. Plots of lnD vsP for all the diffusants show linear relationships with negative slopes, from which activation volume for the diffusion V was calculated. At 90°C, V increases slowly with increasingN and increasingV _Ki, the intrinsic molecular volume of the diffusant, from 39.3 cm³/mol for ethyl caprate (C ₁₃,V _Ki=136 cm³/mol) to 76.8 cm³/mol for behenyl behenate (C₄₅,V _Ki=466 cm³/mol). Observed V s are explainable on the basis of the reptation mode of the chain molecule diffusion. V s for C₂₅ and C₄₅ are found to increase with increasing degree of crystallinity where MDPE, heat-treated MDPE, LDPE, and HDPE were used. The results obtained by varying temperature are as follows. V for C₄₅ was always found to be larger than C₂₅. Both decreased linearly with increasing temperature, giving two linear lines with different slopes whose extensions intersected at 132°C, the melting point of the MDPE, where the difference in V disappeared. The apparent activation energiesE _Ds for the diffusion of C₂₅ and C₄₅ increased linearly with increasing pressure, whose slopes are explainable according toE _D=E ₀+PV [1-(dln V /dlnT) _P ].     

Correlation of volumes and entropies of activation for oxidation of coordinated sulfur in bis-ethylenediaminecobalt(III) complexes by peroxodisulphate,hydrogen peroxide and periodate and for peroxodisulphate oxidation of diimine-cyanide–iron(II) complexes

Activation parameters H , S and V and correlations between S and V are reported for peroxodisulphate oxidation of [Fe(CN)₆]^4–, [Fe(bipy)₃]²⁺ (bipy = (2, 2-bipyridyl), [Fe(phen)₃]²⁺ (phen = 1,10-phenanthroline), cis-[Fe(bipy)₂(CN)₂], [Fe(bipy)(CN)₄]^2–, [Fe(phen)(CN)₄]^2–, [Co(en)₂(glyS)]⁺ (glyS = mercaptoacetate, SCH₂COO^2–), [Co(en)₂(cyS)]⁺ (cyS = cysteinate, SOCH₂CH(COO)NH₂ ^2–) and [Co(en)₂(amS)]²⁺ (amS = ethanesulphenaminate, SCH₂CH₂NH₂ ^–) and for periodate and hydrogen peroxide oxidation of the three last-named complexes. Activation parameters are discussed in terms of electrostriction, solvation and ligand size contributions. Opposite trends for S /V correlations were found for oxidations of Fe^II complexes in comparison with oxidations of coordinated sulphur in the Co^III complexes.     

Molecular structure of N-(2-hydroxyethyl)pyridinium bromide

X-ray diffraction, structural analysis was employed to establish the structure of N-(2-hydroxyethyl)pyridinium bromide, C₇H₁₀NO⁺-Br^–. The plane of the pyridinium ring is twisted by 93 relative to the C-C bond of the side-chain. The N-C-C-O torsion angle is 63.6. The OH bond is oriented toward the heteroaromatic ring. The H-O-C-C torsion angle is 84.4. The molecular packing in the crystal lattice is such that the bromide ions are found between the heteroaromatic rings and the hydrogen bonded to the hydroxyl groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2617–2619, November, 1990.     

Kinetics and mechanism of the interaction of azide with [(H2O)(tap)2RuORu(tap)2-(H2O)]2+ ion at physiological pH

The title reaction has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand], pH and temperature at constant ionic strength. At the physiological pH (7.4) the interaction with azide shows two distinct consecutive steps, i.e., it shows a non-linear dependence on the concentration of N₃ ^–; both processes are [ligand]-dependent. The rate constant for the processes are: k ₁10^–3 s^–1 and k ₂10^–5 s^–1. The activation parameters calculated from Eyring plots are: H ₁ = 14.8 ± 1 kJ mol^–1, S ₁ = –240 ± 3 J K^–1 mol^–1, H ₂ = 44.0 ± 1.5 kJ mol^–1 and S ₂ = –190 ± 4 J K^–1 mol^–1. Based on the kinetic and activation parameters an associative interchange mechanism is proposed for the interaction process. From the temperature dependence of the outersphere association equilibrium constant, the thermodynamic parameters calculated are: H ₁ ⁰ = 4.4 ± 0.9 kJ mol^–1, S ₁ ⁰ = 64 ± 3 J K^–1 mol^–1 and H ₂ ⁰ = 14.2 ± 2.9 kJ mol^–1, S ₂ ⁰ = 90 ± 9 J K^–1 mol^–1, which gives a negative G ⁰ value at all temperatures studied, supporting the spontaneous formation of an outersphere association complex.     

Kinetics of the displacement of aqua ligands from cis-diaqua(ethylenediamine)-platinum(II)perchlorate by adenosine 5′-monophosphate in aqueous medium

The kinetics of the interaction of adenosine 5-monophosphate (5-AMP) with cis-[Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [5-AMP] and temperature at pH 4.0, where the substrate complex exists predominantly as the diaqua species. Both N1 and N7 donor sites of 5-AMP are active for coordination to Pt at this pH. Base stacking and metal-induced macrochelate formation of 5-AMP plays a vital role in determining the concentration limit of 5-AMP during kinetics. Substitution occurs in two consecutive steps; both dependent on the 5-AMP concentration. Activation parameters for both steps have been calculated. The low H ₁ (42.76 ± 1.64 kJ mol^–1) and large negative values of S ₁ (–112.1 ± 5.1 J K^–1 mol^–1) as well as H ₂ (58.1 ± 1.4 kJ mol^–1) and S ₂ (–84.2 ± 4.4 J K^–1 mol^–1) indicate associative modes of activation for both ligand substitution processes in the two consecutive steps.     

Crystal and molecular structure analysis of flutamide. Bifurcated helicoidal C-H ⋯ O hydrogen bonds

Crystal structure determination and semiempirical AM1 and PM3 calculations were performed on flutamide {2-methyl-N[4 nitro-3-(trifluoromethyl) phenyl] propamide}, a powerful nonsteroidal androgen antagonist. The molecule is almost planar apart from CF₃, NO₂, and CH₃ groups. The NO₂ plane makes an angle of 36.3(4) with the least-square plane of the phenyl ring. The molecules are intermolecularly linked by one N-H O and one C-H O hydrogen bonds. A bifurcated helicoidal hydrogen bond network is formed by the intermolecular C-H O hydrogen bond together with another intramolecular C-H O hydrogen bond. The calculated structures are in good agreement with the crystallographic conformations. AM1 is more accurate for predicting the intramolecular C-H O hydrogen bond while PM3 gives a better geometry for the crowded nitro group. AM1 and PM3 charges of benzenic hydrogens are used to predict the propensity of these atoms to form hydrogen bonds. The noncentrosymmetric space group of the crystal (Pna2₁), the calculated dipole moment (8.88 D), and the calculated angle between molecular dipoles and the twofold axis (–49) close to the optimal value (54.7) indicate that flutamide might be a possible candidate for nonlinear optical material.     

The molecular complex of dibenz[a,c]anthracene and trinitrobenzene

The crystal structure of the complex between the polycyclic aromatic hydrocarbon di-benz[a,c]anthracene and 1,3,5-trinitrobenzene is reported. The crystals are triclinic, space group P¯1 with unit cell dimensionsa=7.277(2) å,b=11.237(6) å, andc=13.902(5) å,= 104.13(4),=96.04(3), and =95.15(2). Diffraction data were measured at 121(2) K. The structure was determined and refined toR ₁=0.046. The structure consists of layers containing both dibenz[a,c]anthracene and 1,3,5-trinitrobenzene molecules, interconnected within a layer by C-H O interactions. Layers stack on one another so that dibenz[a,c]anthracene molecules are sandwiched between 1,3,5-trinitrobenzene molecules and vice versa. The average distance between molecules in these sandwiches is 3.23 å.     

Rate constants and mechanism of the reactions of N(4S) atoms with methane and ethane

The channel for the reaction of nitrogen atoms and methane yielding hydrogen atoms does not exceed 10% at 20C. The rate constant for the reaction of nitrogen atoms and ethane at 20C is (4 ± 2)·10^–16 cm³/sec.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 705–706, March, 1990.     

Study of phenolic resin/EVA blends by thermal analysis

The properties of polymeric blends originate from the synergistic association of their components. In this investigation, phenolic resins obtained by the reaction of cashew-nut shell liquid (CNSL) and aldehyde are used in several applications. Mixtures of CNSL with industrial reject ethylene-co-vinyl acetate (EVA reject) were prepared with an EVA reject content up to 70%. The thermal compatibility and stability were evaluated by means of thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). For blends containing a high percentage of EVA reject, the TG curves clearly show two decomposition stages, one at 350C and the other at 450C (onset 467C). The DIG curves of the blend containing 70% CNSL exhibit decomposition at 240C. The DSC curves show that the samples containing a high percentage of EVA reject are incompatible, withT _g values around –30C.The authors would like to thank PETROBRAS/CENPES/DIQUIM for the NMR facilities and thermal measurements.     

Mechanism of oxidation of selenium(IV) by cobalt(III) in perchloric acid — a kinetic study

Summary The kinetics of Co^III oxidation of Se^IV have been studied in aqueous HClO₄. The order with respect to Co^m is two the order with respect to Se^IV is one at low concentrations; two at high concentrations. The latter variation is attributed to the greater reactivity of the Se^IV dimier A mechanism involving complexation between oxidant and substrate is proposed. [CoOH]²⁺ is presumed to be the reactive Co^III species and H₂SeO₃ and HSeO ₃ ^– to be those of Se^IV. At 25° C, E_a, H and S for the monomeric path are 125.6±4.0 kJ mol^–1, 122.1±3.8 kJ mol^–1 and 206±12 JK^–1 mol^–1 respectively and those for the dimeric path are 88.6±3.6 kJ mol^–1, 85.9±3.4 kJ mol^–1 and 62.6±11.3 JK^–1 mol^–1 respectively.     

Effect of the chemical nature of the support on the properties of platinum catalysts for the combined oxidation of CO and H2

The steady-state rate of hydrogen oxidation catalyzed by platinum on an inert support (corundum) is greater than the rate of oxidation of carbon monoxide, while the rate of hydrogen oxidation on a platinum-vanadium catalyst is less than the rate of oxidation of carbon monoxide. The conditions for the complete selective oxidation of the reaction mixture components were determined. Hydrogen is oxidized on the Pt/corundum cataljst at 273K in a non-steady-state mode, while CO is oxidized on the same catalyst at 273 K and on Pt/BaSO₄-V₂O₅ at 383–393K in a steady-state mode.Deceased.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 31, No. 2, pp. 81–85, March–April, 1995.     

Electron diffraction study of the molecular structure of gaseous 1,1-dibromo-3,3,5,5-tetramethyl-1-stanna-3,5-disila-4-oxacyclohexane,Br2Sn(CH2SiMe2)2O

The molecular structure of gaseous Br₂Sn(CH₂SiMe₂)₂O was studied by electron diffraction. The six-membered ring has a chair conformation whereas the entire molecule possessesC _s symmetry. The existence of a boat conformer cannot be completely excluded. The results of theoretical calculations for a twisted-boat conformation are at variance with the experimental data. Steric strain caused by mutual repulsion of the two axial methyl groups is reduced to the tilt of the Me₂Si fragments in opposite directions. This results in an increase (up to 26°C) in the angle formed by the bisector of the C_M-Si-C_M angle with the C_cSiO plane. The main geometrical parameters are as follows:r _g (Å): Si-O 1.708(20); Si-C_M 1.862(20); Si-C_c 1.882(9); Sn-C 2.108(26); Sn-Br 2.456(3); C-H 1.099(30); (degr.): C-Sn-C 105(2); Br-Sn-Br 107.9(1.2); Si-O-Si 129.6(3); C_M-Si-C_M 112; Si-C-H 113 (fixed value in accordance with experiment); C_c-Si-O 107(2); Sn-C-Si 109(2); torsion angles: (Si-C) 52(2); (Si-O) 62(1); (C_c-Sn) 54(1). The average amplitudes were fixed at the values calculated from the force field. Structural parameters of molecules with similar structures were analyzed and compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–387, February, 1993.     

Thermal study of synthesis of cryptohalite

The present work represents a thermal study of synthesis of cryptohalite (Ammonium silicon hexafluoride) by sintering of quartz with ammonium fluoride using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curves indicate that the intensive formation of cryptohalite takes place at 125–155C by an endothermic reaction. Cryptohalite is unstable and dissociates at 320–335C as represented by the sharp and large endothermic peaks at these temperatures.The resulted cryptohalite is colorless in thin sections and crystallizes in cubic system, in the form of octahedral crystals with perfect (111) cleavage. The dimorph bararite is not detected in all runs.

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Zusammenfassung Mittels eines Derivatographen wurde die Synthese von Kryptohalit (Ammoniumsiliziumhexafluorid) durch Sintern von Quarz mit Ammoniumfluorid thermisch untersucht. Die Reaktionsprodukte wurden mikroskopisch und mit Hilfe eines Siemens-Crystalloflex Diffraktometers identifiziert. Die DTA-Kurven zeigen, da\ die intensive Bildung von Kryptohalit in einer endothermen Reaktion bei 125–155C abläuft. Wie durch die scharfen und intensiven endothermen Peaks bei 320–335C gezeigt wird, ist Kryptohalit bei dieser Temperatur instabil und dissoziiert.Das erhaltene Kryptohalit ist in dünnen Schnitten farblos und kristallisiert im kubischen System in der Form von oktaedrischen Kristallen mit perfekter (111) Spaltbarkeit. Das dimorphe Bararit konnte in keinem der Versuche beobachtet werden.

     

Effect of the reduction temperature on the formation and activity of bimetallic Ni-Tc catalysts

The effect of the temperature on the formation, surface state, and catalytic activity in the reactions of dehydrogenation of cyclohexane and dehydrocyclization of n-hexane by Ni-Tc/-Al₂O₃ mono- and bimetallic catalysts was investigated. TcO₂, NiCl₂, and metal phases, and at a high temperature (500–700C), NiAl₂O₄ spinel and Ni-Tc clusters, were found on the surface of all of the catalysts. It was shown that the maximum activity is observed in reduction of monometallic catalysts at 500C and bimetallic catalysts at 700–800C. Synergism appeared in the bimetallic catalysts due to the formation of Ni-Tc clusters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2486–2490, November, 1990.