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1.
Restricted rotation about the naphthalenylcarbonyl bonds in the title compounds resulted in mixtures of cis and trans rotamers, the equilibrium and the rotational barriers depending on the substituents. For 2,7-dimethyl-1,8-di-(p-toluoyl)-naphthalene (1) ΔH° = 3.66 ± 0.14 kJ mol?1, ΔS° = 1.67 ± 0.63 J mol?1 K?1, ΔHct = 55.5 ± 1.3 kJ mol?1, ΔHct = 51.9 ± 1.3 kJ mol?1, ΔSct = ?41.3±4.1 J mol?1 K?1 and ΔSct = ?42.9±4.1 J mol?1 K?1. The rotation about the phenylcarbonyl bond requires ΔH = ?56.9±4.4 kJ mol?1 and ΔS = ?20.5±15.3 J mol?1 K?1 for the cis rotamer, and ΔH = 43.5Δ0.4 kJ mol?1 and ΔS =± ?22.4Δ1.3 J mol?1 K?1 for the trans rotamer. The role of electronic factors is likely to be virtually the same for both these rotamers but steric interaction between the two phenyl rings occurs in the cis rotamer only. Hence, the difference of the activation enthalpies obtained for the cis and trans rotamers, ΔΔH?1 = 13.4 kJ mol?1, provides a basis for the estimation of the role of steric factors in this rotation. For the tetracarboxylic acid 2 and its tetramethyl ester 3 the equilibrium is even more shifted towards the trans form because of enhanced steric and electrostatic interactions between the substituents in the cis form. The barriers for the rotation around the phenylcarbonyl bond and the cis-trans isomerization are lowered; an explanation for this result is presented.  相似文献   

2.
The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k1 ~10?3 s?1 and k2 ~10?5 s?1) and activation parameters (for thioglycolic acid: ΔH1 = 22.4 ± 3.0 kJ mol?1, ΔS1 = ?220 ± 11 J K?1 mol?1, ΔH2 = 38.5 ± 1.3 kJ mol?1, ΔS2 = ?204 ± 4 J K?1 mol?1; for 2‐thiouracil: ΔH1 = 42.2 ± 2.0 kJ mol?1, ΔS1 = ?169 ± 6 J K?1 mol?1, ΔH2 = 66.1 ± 0.5 kJ mol?1, ΔS2 = ?124 ± 2 J K?1 mol?1; for glutathione: ΔH1 = 47.2 ± 1.7 kJ mol?1, ΔS1 = ?155 ± 5 J K?1mol?1, ΔH2 = 73.5 ± 1.1 kJ mol?1, ΔS2 = ?105 ± 3 J K?1 mol?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as   相似文献   

3.
Cobalt Chelates for Hydrogenation Catalysts. II. Hydride Formation with [Co(dmgH)2] and [Co(dpnH)]+ In the presence of benzil as scavanger for the hydridocomplexes [Co(dpnH)]+ and [Co(dmgH)2] the hydride formation in water/n-propanol (50% v/v) becomes the rate determining step, and the ligand hydrogenation is completely suppressed in the case of [Co(dpnH)]+, but only partially in the case of [Co(dmgH)2]. The rate of hydride formation in both cases is 2nd order with respect to the complex, and the activation parameters ([Co(dmgH)2]: ΔH = 48.4 ± 1.0 kJ · mol–1, ΔS = ?57.4 ± 3.4J · mol?1 · K?1, [Co(dpnH)]+: ΔH = 52.7 = 0.4 kJ · mol?1, ΔS = ?59.8 ± 1.2J · mol?1 · K?1) indicate a H2-activation by homolytic splitting for both complexes. Some sources of error and possible causes for the missing activity of [Co(tim)]2+ are discussed.  相似文献   

4.
Cyclohexane and piperidine ring reversal in 1-(3-pentyloxyphenylcarbamoyloxy)-2-dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol?1 and activation parameters ΔG218 = 43.8 ± 0.4 kJ mol?1, ΔH = 48.9 ± 2.5 kJ mol?1 and ΔS = 23 ± 9 J mol?1 K?1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans-pyrrolidinyl derivative. In the trans-piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol?1, ΔH = 55.7 ± 6.3 kJ mol?1 and ΔS = 51 ± 21 J mol?1 K?1 was found for the piperidine ring reversal from the non-equivalence of the α-carbons.  相似文献   

5.
The isomerization of the complex trans-meso-CH3Co(H2O)L2+ (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) to trans-primary, rac-CH3Co(H2O)L2+ has been investigated from pH range 7.11 to 8.09 in aqueous solution. The reaction rate law has been determined as: -d[meso-CH3Co(H2O)L2+]/dt = kOH [OH?][meso-CH3Co(H2O)L2+], where kOH = 600 ± 10 M?1s?1 at 25 °C and μ = 0.5 M. The activation parameters of the reaction were also studied with ΔH± = 19.1 ± 0.9 Kcal mol?1 and ΔS± = 18.0 ± 0.8 cal K?1mol?1. A mechanism that involves a secondary NH inversion is proposed.  相似文献   

6.
It has been confirmed by 1H and 13C NMR spectroscopies that Sn(σ-C7H7)Ph3 undergoes either 1,4- or 1,5-shifts of the SnPh3 moiety around the cycloheptatrienyl ring with ΔH3 = 13.8 ± 0.4 kcal mol?1, ΔS3 = ?5.6 ± 1.2 cal mol?1 deg?1, and ΔG3300 = 15.44 ± 0.14 kcal mol?1. Similarly, (σ-5-cyclohepta-1,3-dienyl)triphenyltin undergoes 1,5-shifts with ΔH3 = 12.4 ± 0.6 kcal mol?1, ΔS3 = ?11.2 ± 1.8 cal mol?1 deg?1, and ΔG3300 = 15.76 ± 0.13 kcal mol?1. It is therefore probable that Sn(σ-5-C5H5)R3 and Sn(σ-3-indenyl)R3 do not undergo 1,2-shifts as previously suggested but really undergo 1,5-shifts.  相似文献   

7.

Ligand substitution of trans-[CoIII(en)2(Me)H2O]2+ was studied for pyrazole, 1,2,4-triazole and N-acetylimidazole as entering nucleophiles. These displace the coordinated H2O molecule trans to the methyl group to form trans-[Co(en)2(Me)azole]. Stability constants at 18°C for the substitution of H2O by pyrazole, 1,2,4-triazole and N-acetylimidazole are 0.7 ± 0.1, 13.8 ± 1.4 and 1.7 ± 0.2 M?1, respectively. Second order rate constants at the same temperature for the reaction of trans-[CoIII(en)2(Me)H2O]2+ with pyrazole, 1,2,4-triazole and N-acetylimidazole are 161 ± 12, 212 ± 11 and 12.9 ± 1.6 M?1 s?1, respectively. Activation parameters (ΔH, ΔS) are 67 ± 6 kJ mol?1, + 27 ± 19 J K?1 mol?1; 59 ± 2 kJ mol?1, + 1 ± 6 J K?1 mol?1 and 72 ± 4 kJ mol?1, + 23 ± 14 J K?1 mol?1 for reactions with pyrazole, 1,2,4-triazole and N-acetylimidazole, respectively. Substitution of coordinated H2O by azoles follows an Id mechanism.  相似文献   

8.
Addition of methoxide to either geometric isomer of the benzylidene complex [(η-C5H5)Re(NO)(PPh3)(CHC6H5)]+PF6? (1t, 1k) affords (η-C5H5)Re(NO)(PPh3)(CH(OCH3)C6H5 (2t, 2k) in which a new chiral center has been generated stereospecifically or with high stereoselectivity. Reaction of 2t and 2k with Ph3C+PF6? results in the chemospecific abstraction of a methoxy group and the stereospecific regeneration of 1t and 1k, respectively.  相似文献   

9.
Ligand substitution kinetics for the reaction [PtIVMe3(X)(NN)]+NaY=[PtIVMe3(Y)(NN)]+NaX, where NN=bipy or phen, X=MeO, CH3COO, or HCOO, and Y=SCN or N3, has been studied in methanol at various temperatures. The kinetic parameters for the reaction are as follows. The reaction of [PtMe3(OMe)(phen)] with NaSCN: k1=36.1±10.0 s−1; ΔH1=65.9±14.2 kJ mol−1; ΔS1=6±47 J mol−1 K−1; k−2=0.0355±0.0034 s−1; ΔH−2=63.8±1.1 kJ mol−1; ΔS−2=−58.8±3.6 J mol−1 K−1; and k−1/k2=148±19. The reaction of [PtMe3(OAc)(bipy)] with NaN3: k1=26.2±0.1 s−1; ΔH1=60.5±6.6 kJ mol−1; ΔS1=−14±22 J mol−1K−1; k−2=0.134±0.081 s−1; ΔH−2=74.1±24.3 kJ mol−1; ΔS−2=−10±82 J mol−1K−1; and k−1/k2=0.479±0.012. The reaction of [PtMe3(OAc)(bipy)] with NaSCN: k1=26.4±0.3 s−1; ΔH1=59.6±6.7 kJ mol−1; ΔS1=−17±23 J mol−1K−1; k−2=0.174±0.200 s−1; ΔH−2=62.7±10.3 kJ mol−1; ΔS−2=−48±35 J mol−1K−1; and k−1/k2=1.01±0.08. The reaction of [PtMe3(OOCH)(bipy)] with NaN3: k1=36.8±0.3 s−1; ΔH1=66.4±4.7 kJ mol−1; ΔS1=7±16 J mol−1K−1; k−2=0.164±0.076 s−1; ΔH−2=47.0±18.1 kJ mol−1; ΔS−2=−101±61 J mol−1 K−1; and k−1/k2=5.90±0.18. The reaction of [PtMe3(OOCH)(bipy)] with NaSCN: k1 =33.5±0.2 s−1; ΔH1=58.0±0.4 kJ mol−1; ΔS1=−20.5±1.6 J mol−1 K−1; k−2=0.222±0.083 s−1; ΔH−2=54.9±6.3 kJ mol−1; ΔS−2=−73.0±21.3 J mol−1 K−1; and k−1/k2=12.0±0.3. Conditional pseudo-first-order rate constant k0 increased linearly with the concentration of NaY, while it decreased drastically with the concentration of NaX. Some plausible mechanisms were examined, and the following mechanism was proposed. [Note to reader: Please see article pdf to view this scheme.] © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 523–532, 1998  相似文献   

10.
The reaction between chromium(VI) and L-ascorbic acid has been studied by spectrophotometry in the presence of aqueous citrate buffers in the pH range 5.69–7.21. The reaction is slowed down by an increase of the ionic strength. At constant ionic strength, manganese(II) ion does not exert any appreciable inhibition effect on the reaction rate. The rate law found is where Kp is the equilibrium constant for protonation of chromate ion and kr is the rate constant for the redox reaction between the active forms of the oxidant (hydrogenchromate ion) and the reductant (L-hydrogenascorbate ion). The activation parameters associated with rate constant kr are Ea = 20.4 ± 0.9 kJ mol?1, ΔH = 17.9 ± 0.9 kJ mol?1, and ΔS=?152 ± 3 J K?1 mol?1. The reaction thermodynamic magnitudes associated with equilibrium constant Kp are ΔH0 = 16.5 ± 1.1 kJ mol?1 and ΔS0 = 167 ± 4 J K?1 mol?1. A mechanism in accordance with the experimental data is proposed for the reaction. © 1993 John Wiley & Sons, Inc.  相似文献   

11.
Proton affinities of a series of triphenyl Group Va compounds have been determined by bracketing using reactant ion monitoring: (C6H5)3N = 904 ± 8 kJ mol?1, (C6H5)3P = 968 ± 5 kJ mol?1, (C6H5)3As = 904 ± 8 kJ mol?1 and (C6H5)3Sb = 846 ± 8 kJ mol?1. The large difference in substituent effect of phenyl for hydrogen between As or P and N may result from overlap of the 2p orbitals of N with the sp2 orbitals on the ring carbons and lack of overlap for P or As. Proton affinities of phenylalkylphosphine oxides are essentially the same, 904 ± 8 kJ mol?1, independent of alkyl group.  相似文献   

12.
2D 1H-1H EXSY NMR spectroscopy show that the free energy of activation ΔG in six 3-allyl-3-borabicyclo[3.3.1]nonane derivatives is significantly higher (72–86 kJ mol?1) than that in typical allylboranes (48–66 kJ mol?1). For the first member of the series, viz., 3-allyl-3-borabicyclo[3.3.1]nonane, the activation parameters of the permanent allylic rearrangement were also determined (ΔH = 82.7±3.4 kJ mol?1, ΔS = ?11.8±10.3 J mol?1 K?1, E A = 85.5±3.4 kJ mol?1, lnA = 29.2±1.2).  相似文献   

13.
The heat of formation of benzophenone oxide, Ph2CO2, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph2CN2 + O2 → Ph2CO2 + N2 was found to be ?48.0 ±0.8 kcal mol?1 and ΔHf(Ph2CN2) was determined by measuring the reaction enthalpy for Ph2CN2 + EtOH → Ph2CHOEt + N2 (?53.6 ±1.0 kcal mol?1). Taking ΔHf(PhCHOEt) = ?10.6 kcal mol?1 led to ΔHf(Ph2CN2) = 99.2 ± 1.5 kcal mol?1 and hence to ΔHf(Ph2CO2) = 51.1 ± 2.0 kcal mol?1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph2CO2 → 2Ph2CO + O2 is exothermic by ?76.0 ±4.0 kcal mol?1.  相似文献   

14.
Reactions of Fe+ and FeL+ [L=O, C4H6, c-C5H6, C5H5, C6H6, C5H4(=CH2)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe+, Fe(C5H5)+, and FeC6H 6 + yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC4H 6 + and Fe(c-C5H6)+], as well as FeC5H4(=CH2)+ and FeO+, are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC4H6 +, Fe(c-C5H6)+, and FeC5H4(=CH2)+. In addition, FeC4H 6 + and Fe(c-C5H6)+ cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C5H6)+ with pyrrole and thiophene is hydrogen-atom displacement, which implies DO(Fa(N5H5)+-C4H4X)>DO(Fe(C5H5)+-H)=46±5 kcal mol?1. DO(Fe+-C4H4S) and DO(Fe+-C4H5N)=DO(Fe+-C4H6)=48±5 kcal mol?1. Finally, 55±5 kcal mol?1=DO(Fe+-C6H6)>DO(Fe+-C4H4O)>DO(Fe+-C2H4)=39.9±1.4 kcal mol?1. FeO+ reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. DO(Fe+-CS)>DO(Fe+-C4H4S)≈48±5 kcal mol?1 and DO(Fe+-C4H5N)≈48±5 kcal mol?1>DO(Fe+-HCN)>DO(Fe+-C2H4)=39.9±1.4 kcal mil?1.  相似文献   

15.
Kinetics of the complex formation of chromium(III) with alanine in aqueous medium has been studied at 45, 50, and 55°C, pH 3.3–4.4, and μ = 1 M (KNO3). Under pseudo first-order conditions the observed rate constant (kobs) was found to follow the rate equation: Values of the rate parameters (kan, k, KIP, and K) were calculated. Activation parameters for anation rate constants, ΔH(kan) = 25 ± 1 kJ mol?1, ΔH(k) = 91 ± 3 kJ mol?1, and ΔS(kan) = ?244 ± 3 JK?1 mol?1, ΔS(k) = ?30 ± 10 JK?1 mol?1 are indicative of an (Ia) mechanism for kan and (Id) mechanism for k routes (‥substrate Cr(H2O) is involved in the k route whereas Cr(H2O)5OH2+ is involved in k′ route). Thermodynamic parameters for ion-pair formation constants are found to be ΔH°(KIP) = 12 ± 1 kJ mol?1, ΔH°(K) = ?13 ± 3 kJ mol?1 and ΔS°(KIP) = 47 ± 2 JK?1 mol?1, and ΔS°(K) = 20 ± 9 JK?1 mol?1.  相似文献   

16.
The product from reaction of lanthanum chloride heptahydrate with salicylic acid and thioproline, [La(Hsal)2•(tch)]•2H2O, was synthesized and characterized by IR, elemental analysis, molar conductance, thermogravimatric analysis and chemistry analysis. The standard molar enthalpies of solution of LaCl3•7H2O (s), [2C7H6O3 (s)], C4H7NO2S (s) and [La(Hsal)2•(tch)]•2H2O (s) in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide (DMSO) and 3 mol•L-1 HCl were determined by calorimetry to be [LaCl3•7H2O (s), 298.15 K]=(-102.36±0.66) kJ•mol-1, [2C7H6O3 (s), 298.15 K]=(26.65±0.22) kJ•mol-1, [C4H7NO2S (s), 298.15 K]=(-21.79±0.35) kJ•mol-1 and {[La(Hsal)2•(tch)]•2H2O (s), 298.15 K}=(-41.10±0.32) kJ•mol-1. The enthalpy change of the reaction LaCl3•7H2O (s)+2C7H6O3 (s)+C4H7NO2S (s)=[La(Hsal)2•(tch)]•2H2O (s)+3HCl (g)+5H2O (l) (Eq. 1) was determined to be =(41.02±0.85) kJ•mol-1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of [La(Hsal)2•(tch)]•2H2O (s) was estimated to be {[La(Hsal)2•(tch)]•2H2O (s), 298.15 K}=(-3017.0±3.7) kJ•mol-1.  相似文献   

17.
The anionic gold(I) complexes [1‐(Ph3PAu)‐closo‐1‐CB11H11]? ( 1 ), [1‐(Ph3PAu)‐closo‐1‐CB9H9]? ( 2 ), and [2‐(Ph3PAu)‐closo‐2‐CB9H9]? ( 3 ) with gold–carbon 2c–2e σ bonds have been prepared from [AuCl(PPh3)] and the respective carba‐closo‐borate dianion. The anions have been isolated as their Cs+ salts and the corresponding [Et4N]+ salts were obtained by salt metathesis reactions. The salt Cs‐ 3 isomerizes in the solid state and in solution at elevated temperatures to Cs‐ 2 with ΔHiso=(?75±5) kJ mol?1 (solid state) and ΔH=(118±10) kJ mol?1 (solution). The compounds were characterized by vibrational and multi‐NMR spectroscopies, mass spectrometry, elemental analysis, and differential scanning calorimetry. The crystal structures of [Et4N]‐ 1 , [Et4N]‐ 2 , and [Et4N]‐ 3 were determined. The bonding parameters, NMR chemical shifts, and the isomerization enthalpy of Cs‐ 3 to Cs‐ 2 are compared to theoretical data.  相似文献   

18.
Appearance energies for [C7H5O]+ fragment ions, formed from a variety of benzoyl compounds, have been measured by photon impact. The mean heat of formation calculated for [C7H5O]+ is 705 ± 6 kJ mol?1, which can be correlated with either a single threshold structure or a mixture of structures with similar heats of formation. Previously observed variations of ΔHf([C7H5O]+) with precursor molecule are shown to be consistent with a structure dependent kinetic shift, rather than the presence of isolated electronic states.  相似文献   

19.
The product from reaction of samarium chloride hexahydrate with salicylic acid and Thioproline, [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O, was synthesized and characterized by IR, elemental analysis, molar conductance, and thermogravimetric analysis. The standard molar enthalpies of solution of [SmCl3·6H2O(s)], [2C7H6O3(s)], [C4H7NO2S(s)] and [Sm(C7H5O3)2·(C4H7NO2S)·H2O(s)] in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide(DMSO) and 3 mol L?1 HCl were determined by calorimetry to be Δs H m Φ [SmCl3 δ6H2O (s), 298.15 K]= ?46.68±0.15 kJ mol?1 Δs H m Φ [2C7H6O3 (s), 298.15 K]= 25.19±0.02 kJ mol?1, Δs H m Φ [C4H7NO2S (s), 298.15 K]=16.20±0.17 kJ mol?1 and Δs H m Φ [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O (s), 298.15 K]= ?81.24±0.67 kJ mol?1. The enthalpy change of the reaction (1) $$ SmCl_3 \cdot 6H_2 O(s) + 2C_7 H_6 O_3 (s) + C_4 H_7 NO_2 S(s) = Sm(C_7 H_5 O_3 )_2 \cdot (C_4 H_6 NO_2 S) \cdot 2H_2 O(s) + 3HCl(g) + 4H_2 O(1) $$ was determined to be Δs H m Φ =123.45±0.71 kJ mol?1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of Sm(C7H5O3)2(C4H6NO2S)δ2H2O(s) was estimated to be Δs H m Φ [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O(s), 298.15 K]= ?2912.03±3.10 kJ mol?1.  相似文献   

20.
Low-temperature heat capacity of polynuclear Fe(HTrz)3(B10H10)·H2O (I) and trinuclear [Fe3(PrTrz)6(ReO4)4(H2O)2](ReO4)2 (II) spin crossover coordination compounds was measured in 80–300 K temperature range using a vacuum adiabatic calorimeter. For I, an anomaly of heat capacity with a maximum at T trs=234.5 K (heating mode) was observed, Δtrs H=10.1±0.2 kJ mol?1 Δtrs S=43.0±0.8 J mol? K?1. For II, a smooth anomaly between 150 and 230 K was found, Δtrs H=2.5±0.25 kJ mol?1 Δtrs S=13.6±1.4 J mol? K?1. Anomalies observed in both compounds correspond to 1A1?5T2 spin transition.  相似文献   

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