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1.
Defined-sector explicit solvent in the continuum model approach for computational prediction of pK a
《Molecular physics》2012,110(19-20):2401-2412
Accurate prediction of the acidity dissociation constant (K a) is a challenge for the theory of proton-transfer reactions, making first-principles prediction of pK a within 0.5?pK units of experimental values a benchmark of broad interest. In the present contribution, the defined-sector explicit solvent in continuum cluster model, which considers the structure-to-chemical affinity relationship of the carboxyl functional group, is presented. The model demonstrates predictable solvent networks based on established ‘preferred’ conformations found in a training set. Predictability within 1?kcal?mol–1 accuracy is shown for a full set of carboxylic acid systems with varying functionality. 相似文献
2.
Kinetics and mechanism of the anilinolysis of aryl 4‐nitrophenyl thionocarbonates in aqueous ethanol
Enrique A. Castro Rayen Acevedo José G. Santos 《Journal of Physical Organic Chemistry》2011,24(7):603-610
The reactions of bis(4‐nitrophenyl), 3‐chlorophenyl 4‐nitrophenyl, and 3‐methoxyphenyl 4‐nitrophenyl thionocarbonates ( 1 , 2 , and 3 , respectively) with a series of anilines are subjected to a kinetic investigation in 44 wt.% ethanol–water, at 25.0 °C and an ionic strength of 0.2 M. Under aniline excess, pseudo‐first‐order rate coefficients (kobs) are found. Plots of kobs versus aniline concentration are linear, with the slopes (kN) pH independent, kN being the rate coefficient for the anilinolysis of the thionocarbonates. The Brønsted plot (log kN vs. pKa of anilinium ions) for thionocarbonate 1 is linear, with slope (β) 0.62, which is consistent with a concerted mechanism. The Brønsted plots for thionocarbonates 2 and 3 are curved, with slopes 0.1 at high pKa for both reaction series and slopes 0.84 and 0.79 at low pKa for the reactions of 2 and 3 , respectively. The latter plots are in accordance to stepwise mechanisms, through a zwitterionic tetrahedral intermediate (T±) and its anionic analogue (T?), the latter being formed by deprotonation of T± by the basic form of the buffer (HPO). The Brønsted curves are explained by a change in the rate‐limiting step, from deprotonation of T± at low pKa, to its formation at high pKa. The influence of the amine nature and the non‐leaving and electrophilic groups of the substrate on the kinetics and mechanism is also discussed. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
3.
David R. Edwards Christopher I. Maxwell Robert W. Harkness Alexei A. Neverov Nicholas J. Mosey R. Stan Brown 《Journal of Physical Organic Chemistry》2012,25(3):258-266
An experimental determination of the βEq value for equilibrium transfer of the O,O‐dimethyl phosphorothioyl group between oxyanion nucleophiles in water and methanol at 25 °C is presented. The respective βEq values in the two solvents are experimentally the same at ?1.45 ± 0.08 and ?1.39 ± 0.12. Based on the observation that the Brønsted correlation for the nucleophilic reaction of phenoxides in water with substrate 1d (dimethyl 4‐nitrophenyl phosphorothioate, pKaHOAr of 7.14) is linear over the entire range of phenoxides employed (5.53 ≤ pKaNu ≤ 12.38), the reaction for phenoxide nucleophiles displacing phenoxide leaving groups is probably concerted. The obtained data allow one to calculate, for a symmetrical transition state involving 2,4,5‐trichlorophenoxide as a nucleophile and leaving group, an approximately 60% P–OAr cleavage and about 40% P–Nuc bond formation. A computational method is presented for the rapid prediction of the βEq values for such processes in water and methanol, and the results are compared with known values from the literature. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
4.
V. Koptev M. Nekipelov M. Büscher S. Dymov M. Hartmann V. Hejny H.R. Koch N. Lang S. Mikirtichyants H. Ohm A. Petrus Z. Rudy R. Schleichert A. Sibirtsev K. Sistemich H. Ströher K.-H. Watzlawik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):235-240
Results of a first experiment on (K+p) and (K+d) correlations from proton-carbon (pC) and proton-deuteron (pd) interactions at beam energies above and much below the threshold for elementary kaon production in nucleon-nucleon reactions
( T
NN = 1580 MeV) are discussed. These data, obtained with the ANKE spectrometer at COSY-Jülich, provide first direct evidence
for K+ production via the two-step mechanism and an indication for a cluster mechanism. It is shown that both processes contribute
significantly in pC collisions at 1200 MeV, while they are strongly suppressed at 2300 MeV and also in pd-interactions at 1344 MeV. It is emphasized that the underlying kinematics can be exploited to distinguish between these reaction
mechanisms.
Received: 26 November 2002 / Accepted: 26 March 2003 / Published online: 20 May 2003 相似文献
5.
Enrique A. Castro Margarita Aliaga Paola R. Campodonico J. Ramón Leis Luis García‐Río José G. Santos 《Journal of Physical Organic Chemistry》2008,21(2):102-107
The reactions of quinuclidines with phenyl, 4‐chlorophenyl, 4‐cyanophenyl, and 4‐nitrophenyl chlorothionoformates ( 1 , 2 , 3 , and 4 , respectively) are subjected to a kinetic study in aqueous solution, at 25.0°C, and an ionic strength of 0.2 M (KCl). The reactions are studied by following spectrophotometrically the release of the corresponding phenoxide anion/phenol generated in the parallel hydrolysis of the substrates. Under amine excess, pseudo‐first‐order rate coefficients (kobs) are found. Plots of kobs versus [amine] are linear, with slope kN. The Brønsted‐type plots (log kN vs. pKa of aminium ions) are linear, with slopes β = 0.26, 0.22, 0.19, and 0.28 for the reactions with 1 , 2 , 3 , and 4 , respectively. The magnitudes of the slopes indicate that these mechanisms are stepwise, with rate‐determining formation of a zwitterionic tetrahedral intermediate (T±). A dual parametric equation with the pKa of the nucleophiles and non‐leaving groups show βN = 0.26 and β nlg = ?0.16, also in accordance with the proposed mechanism. On the other hand, the reactivity of these thiocarbonyl substrates and their carbonyl derivatives was studied using their hardness index and compared with their experimental parameters, confirming the proposed mechanisms. By comparison of the title reactions with similar aminolyses, the following conclusions arise: (i) The mechanism of the reactions under investigation is stepwise with rate‐determining formation of T±. (ii) The reactivity of the substrates toward quinuclidines follows the order 4 > 3 > 2 > 1 . (iii) Quinuclidines are more reactive than isobasic pyridines toward chlorothionoformates. (iv) Chlorothionoformates are less reactive than chloroformates towards quinuclidines in accordance with the HSAB principle. (v) The kN values for phenyl chloroformate and 4 can be correlated with the pKa of quinuclidines and also with the hardness values calculated by the HF/3‐21G level of theory. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
6.
Enrique A. Castro Marcela Gazitúa José G. Santos 《Journal of Physical Organic Chemistry》2009,22(11):1030-1037
The reactions of pyridines and secondary alicyclic (SA) amines with phenyl and 4‐nitrophenyl chlorodithioformates (PClDTF and NPClDTF, respectively) are subjected to a kinetic study in aqueous ethanol (44 wt% ethanol) solution, at 25.0 °C, and an ionic strength of 0.2 M (KCl). The reactions are studied spectrophotometrically. Under amine excess, pseudo‐first‐order rate coefficients (kobs) are found. Plots of kobs versus [amine] are linear and pH independent, with slope kN. The Brønsted‐type plots (log kN vs. pKa of aminium ions) are linear for the reactions of PClDTF with SA amines (slope β of 0.3) and pyridines (β = 0.26) and those of NPClDTF with pyridines (β = 0.30). For the reaction of NPClDTF with SA amines the Brønsted‐type plot is biphasic, with slopes β1 = 0.2 (at high pKa) and β2 = 1.1 (at low pKa). The pKa value at the center of curvature (pK) is 7.7. The magnitude of the slopes indicates that the mechanisms of these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate as the rate‐determining step, except for the reaction of NPClDTF with SA amines where there is a change in the rate‐determining step, from formation to breakdown of the tetrahedral intermediate, as the amine basicity decreases. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
Vladislav M. Vlasov 《Journal of Physical Organic Chemistry》2012,25(4):296-308
Variation of the activation parameters in the SN2, acyl‐transfer, SNAr, SNV, and AdN reactions offers a uniquely useful probe for the mechanistic features of these reactions in solution. New approach uses the substituent effects on the aromatic ring to the variation of the activation parameters, ΔH≠ and ΔS≠, in the above reactions in the frameworks of the Hammett‐like equations in order to evaluate the resultant δΔH≠ and δΔS≠ reaction constants. Compensation relationships of δΔH≠ versus δΔS≠ allow one to estimate the contribution of changes of the internal enthalpy, δΔH≠int, to the enthalpy reaction constant, δΔH≠, that is inherent to bimolecular nucleophilic reactions and gives a single linear dependence on the Hammett ρ reaction constants for these reactions. The deviations from dependence of δΔH≠int versus ρ serve as useful points of interpretation of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the substrates, nucleophiles, and leaving groups on the mechanistic features in bimolecular nucleophilic reactions are governed by the magnitude of δΔH≠int. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
8.
Petr K. Sazonov Galina A. Artamkina Irina P. Beletskaya 《Journal of Physical Organic Chemistry》2008,21(3):198-206
Second order rate constants are reported for the reactions of metal carbonyl anions ([M(CO)nL]?) with several vinyl halides: PhCCl?C(CN)2, Z‐ and E‐Ph(CN)C?CHHal (Hal = Cl, Br) which follow the addition–elimination (AdNE) substitution mechanism. The obtained data show that the nucleophilic reactivity of [M(CO)nL]? anions towards vinyl halides increases in the same order as in aliphatic SN2 reactions, but much more steeply, by 14 orders of magnitude in the row log{ }: [CpFe(CO)2]? (~14), [Re(CO)5]? (7.8), [Mn(CO)5]? 2.1, [CpW(CO)3]? (0.7) > [CpMo(CO)3]? (0). A good correlation exists between nucleophilicities of [M(CO)nL]? anions towards vinyl (sp2‐carbon) and alkyl halides (sp3‐carbon) with slope 2.7. The reactivity of [M(CO)nL]? in a halogen–metal exchange process (with Z‐PhC(CN)?CHI) follows a similar ‘large’ scale as in the AdNE process. The nucleophilicity of [M(CO)nL]? anions correlates better with their one‐electron oxidation potentials (Eox) than with their basicity (pKa of [M(CO)nL]H). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
Sergey L. Khursan Mikhail Yu. Ovchinnikov 《Journal of Physical Organic Chemistry》2014,27(12):926-934
A scheme for the pKa estimation of organic acids in dimethylsulfoxide (DMSO) solution based on quantum chemical calculations is proposed. The procedure of pKa calculation requires several steps. The first is the calculation of the gas phase acidity of the compound. The G3MP2B3, G4MP2 as well as CBS‐QB3 composite methods made it possible to estimate values of gas phase acidities of an extensive set of structures with a high confidence level (standard deviations equal to 1.15, 1.13 and 1.29 kcal mol?1, respectively; the test set included 91 compounds). The second step is the computation of the solvation correction with the integral equation formalism version of polarizable continuum model (IEF‐PCM)–B3LYP/6‐311+G(d,p) approximation. Within the bounds of our approach, the medium properties were covered only by the PCM model, i.e. the proposed procedure neglects specific interactions between DMSO and the solute. It was determined that the approach to pKa estimation mentioned above is the most balanced in terms of accuracy, resource intensity and computation time cost. In the third step, the error of the pKa calculation was decreased by correlation allowances. Correlation allowances were determined for each acid class (62 С―Н, 55 N―Н, 24 O―Н and 5 S―Н acids) in the range of 50 units in terms of logarithmic scale using the test set including 146 compounds. Seven O―H acids showing the ability to form cyclic dimers were separated into a discrete group. The proposed methodology was applied to the estimation of pKa for trans‐ and cis‐dimethyl‐4,5‐dihydro‐3H‐pyrazol‐3,5‐dicarboxylates as well as for 5‐fluorouracil subject to competitive dissociation, the latter by N1―H or N3―H bonds. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
Ju‐Young Kim Dong Wook Kim Choong Eui Song Dae Yoon Chi Sungyul Lee 《Journal of Physical Organic Chemistry》2013,26(1):9-14
We present a mechanistic study for nucleophilic substitution (SN2) reactions facilitated by multifunctional n‐oligoethylene glycols (n‐oligoEGs) using alkali metal salts MX (M+ = Cs+, K+, X– = F–, Br–, I–, CN–) as nucleophilic agents. Density functional theory method is employed to elucidate the underlying mechanism of the SN2 reaction. We found that the nucleophiles react as ion pairs, whose metal cation is ‘coordinated’ by the oxygen atoms in oligoEGs acting as Lewis base to reduce the unfavorable electrostatic effects of M+ on X–. The two terminal hydroxyl (?OH) function as ‘anchors’ to collect the nucleophile and the substrate in an ideal configuration for the reaction. Calculated barriers of the reactions are in excellent agreement with all experimentally observed trends of SN2 yields obtained by using various metal cations, nucleophiles and oligoEGs. The reaction barriers are calculated to decrease from triEG to pentaEG, in agreement with the experimentally observed order of efficiency (triEG < tetraEG < pentaEG). The observed relative efficiency of the metal cations Cs+ versus K+ is also nicely demonstrated (larger [better] barrier [efficiency] for Cs+ than for K+). We also examine the effects of the nucleophiles (F–, Br–, I–, CN–), finding that the magnitudes of reaction barriers are F– > CN– > Br– > I–, elucidating the observation that the yield was lowest for F–. It is suggested that the role of oxygen atoms in the promoters is equivalent to that of –OH group in bulky alcohols (tert‐butyl or amyl‐alcohol) for SN2 fluorination reactions previously studied in our lab. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献