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1.
Klaus Rakus Sergej P. Verevkin Hans-Dieter Beckhaus Christoph Rüchardt 《欧洲无机化学杂志》1994,127(11):2225-2234
The thermolysis reactions of the tricyanomethyl compounds 10a-c were studied in solution. 2,2-Dicyano-3-methyl-3-phenylbutyronitrile ( 10a ) and 2,2-dicyano-3-methyl-3-(4-nitrophenyl)butyronitrile ( 10b ) decomposed heterolytically into carbenium ions and (CN)3C− anions, while 9-methyl-9-(tricyanomethyl)fluorene ( 10c ) underwent about 11% homolytic C-C bond cleavage into 9-methyl-9-fluorenyl- and tricyanomethyl radicals. The rates of the homolysis were determined by a radical scavenger procedure under conditions of pseudozero order kinetics. From the temperature effect on the rate constants the activation parameters were determined [ΔH ( 10c ) = 155· 2 kJ mol−1, ΔS ( 10c ) = 58· 5 J mol−1 K−1]. Standard enthalpies of formation ΔH (g) were determined for 2,2-dicyanopropionitrile ( 2 ) (422.45 kJ mol−1), 2,2-dicyanohexanenitrile ( 3 ) (349.74 kJ mol−1), 2,2-dicyano-3-phenylpropionitrile ( 4 ) (540.75 kJ mol−1), 2-butyl-2-methylhexanentrile ( 5 ) (-133.20 kJ mol−1), 2,2-dimethylpentanenitrile ( 6 ) (-45.78 kJ mol−1), and 2-methylbutyronitrile ( 7 ) (2.44 kJ mol−1) from the enthalpies of combustion and enthalpies of sublimation/vaporization. From these data and known Δ (g) values for alkanenitriles and -dinitriles, thermochemical increments for ΔH (g) were derived for alkyl groups with one, two, or three cyano groups attached. The comparison of these increments with those of alkanes reveals a strong geminal destabilization, which is interpreted by dipolar repulsions between the cyano groups. - From ΔH (g) of 10c and ΔH of its homolytic decomposition the radical stabilization enthalpy for the tricyanomethyl radical 1 RSE ( 1 ) = -18 kJ mol−1 was determined. Thus, 1 is destabilized, in comparison with the RSEs of tertiary α-cyanalkyl (23 kJ mol−1) and α,α-dicyanoalkyl (27 kJ mol−1) radicals, which were recalculated from bond homolysis measurements[4] and the new thermochemical data. This change of RSE on increasing the number of α-cyano groups is discussed as the result of the additive contributions by resonance stabilization and increasing destabilization by dipolar repulsion. The amount of the dipolar energies was estimated by molecular mechanics (MM2). 相似文献
2.
Luis F. Pacios Víctor M. Campos Irene Merino Luis Gómez 《Journal of computational chemistry》2009,30(15):2420-2432
A key step in the metabolic degradation of biphenyl xenobiotics is catechol formation upon dehydrogenation of cis‐ and trans‐dihydrodiols in prokaryotic and eukaryotic pathways, respectively. Structure and thermodynamics of stereoisomers of cis‐, trans‐2,3‐biphenyl‐dihydrodiols ( I ) and their dehydrogenation products (hydroxyketones, II ), as well as final catechol (2,3‐biphenyldiol, III ) are studied by means of ab initio MP2/6‐311++G(2df,2p)//MP2/6‐311G(d,p) calculations. Formation of stereoisomers I and II is exothermic and endergonic, whereas III is enthalpically and entropically driven. Dehydrogenations are endothermic (ΔH ~ 1.5–4 kcal mol?1) and exergonic (ΔG ~ ?5 to ?7.5 kcal mol?1) without noticeable differences between cis and trans pathways, although the same keto stereoisomer II ‐(2S) is found to be the more favored product from both cis‐ and trans‐ I . The final II → III tautomerization is thermodynamically enhanced (ΔH ~ ?27, ΔG ~ ?28 kcal mol?1) but the process is shown to have a large activation energy if it had to occur via unimolecular path. Although this tautomerization is generally assumed to be a nonenzymatic process as it involves rearomatization of an oxygenated ring, proton transfer with an anionic intermediate might be a more probable process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
3.
Ondrej Kysel Šimon Budzák Miroslav Medveď Pavel Mach 《International journal of quantum chemistry》2008,108(9):1533-1545
Geometry, thermodynamic, and electric properties of the π‐EDA complex between hexamethylbenzene (HMB) and tetracyanoethylene (TCNE) are investigated at the MP2/6‐31G* and, partly, DFT‐D/6‐31G* levels. Solvent effects on the properties are evaluated using the PCM model. Fully optimized HMB–TCNE geometry in gas phase is a stacking complex with an interplanar distance 2.87 × 10?10 m and the corresponding BSSE corrected interaction energy is ?51.3 kJ mol?1. As expected, the interplanar distance is much shorter in comparison with HF and DFT results. However the crystal structures of both (HMB)2–TCNE and HMB–TCNE complexes have interplanar distances somewhat larger (3.18 and 3.28 × 10?10 m, respectively) than our MP2 gas phase value. Our estimate of the distance in CCl4 on the basis of PCM solvent effect study is also larger (3.06–3.16 × 10?10 m). The calculated enthalpy, entropy, Gibbs energy, and equilibrium constant of HMB–TCNE complex formation in gas phase are: ΔH0 = ?61.59 kJ mol?1, ΔS = ?143 J mol?1 K?1, ΔG0 = ?18.97 kJ mol?1, and K = 2,100 dm3 mol?1. Experimental data, however, measured in CCl4 are significantly lower: ΔH0 = ?34 kJ mol?1, ΔS = ?70.4 J mol?1 K?1, ΔG0 = ?13.01 kJ mol?1, and K = 190 dm3 mol?1. The differences are caused by solvation effects which stabilize more the isolated components than the complex. The total solvent destabilization of Gibbs energy of the complex relatively to that of components is equal to 5.9 kJ mol?1 which is very close to our PCM value 6.5 kJ mol?1. MP2/6‐31G* dipole moment and polarizabilities are in reasonable agreement with experiment (3.56 D versus 2.8 D for dipole moment). The difference here is due to solvent effect which enlarges interplanar distance and thus decreases dipole moment value. The MP2/6‐31G* study supplemented by DFT‐D parameterization for enthalpy calculation, and by the PCM approach to include solvent effect seems to be proper tools to elucidate the properties of π‐EDA complexes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 相似文献
4.
The kinetics of formation and dissociation of [V(H2O)5NCS]2+ have been studied, as a function of excess metal-ion concentration, temperature, and pressure, by the stopped-flow technique. The thermodynamic stability of the complex was also determined spectrophotometrically. The kinetic and equilibrium data were submitted to a combined analysis. The rate constants and activation parameters for the formation (f) and dissociation (r) of the complex are: k/M ?1 · S?1 = 126.4, k/s?1 = 0.82; ΔH /kJ · mol?1 = 49.1, ΔH/kJ · mol?1 = 60.6; ΔS/ J·K?1·mol?1= ?39.8, ΔSJ·K?1·mol?1 = ?43.4; ΔV/cm3·mol?1 = ?9.4, and ΔV/cm3 · mol?1 =?17.9. The equilibrium constant for the formation of the monoisothiocynato complex is K298/M ?1 = 152.9, and the enthalpy and entropy of reaction are ΔH0/kJ · mol?1 = ? 11.4 and ΔS0/J. K?1mol?1 = +3.6. The reaction volume is ΔV0/cm3· mol?1 = +8.5. The activation parameters for the complex-formation step are similar to those for the water exchange on [V(H2O)6]3+ obtained previously by NMR techniques. The activation volumes for the two processes are consistent with an associative interchange, Ia, mechanism. 相似文献
5.
Ab initio calculations at the CCSD(T)/6‐311++G(2d,p)//B3LYP/6‐311++G(d,p) level of theory have been carried out for three prototypical rearrangement processes of organosilicon anion systems. The first two are reactions of enolate ions which involve oxygen–silicon bond formation via three‐ and four‐membered states, respectively. The overall reactions are: The ΔG (reaction) values for the two processes are +175 and +51 kJ mol?1, with maximum barriers (to the highest transition state) of +55 and +159 kJ mol?1, respectively. The third studied process is the following: (CH3O)C(?CH2)Si(CH3)2CH → (CH3)2(C2H5)Si? + CH2CO, a process involving an SNi reaction between ‐CH and CH3O‐ followed by silicon–carbon bond cleavage. The reaction is favourable [ΔG(reaction) = ?39 kJ mol?1] with the barrier for the SNi process being 175 kJ mol?1. The previous experimental and the current theoretical data are complementary and in agreement. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
Paul Von Ragué Schleyer José Walkimar De M. Carneiro 《Journal of computational chemistry》1992,13(8):997-1003
The closely related Cs ( 1 ) and C2v ( 3 ) structures of CH have been reinvestigated at many ab initio levels using MP2/6-31G** and MP2/6-311 + + G(2df, 2pd) geometries. The largest basis sets employed were 6-311G(3df, 2p), 6-311 + + G(3df, 3pd), and the Dunning “correlation consistent” polarized triple-split valence basis set (cc-pVTZ). Electron correlation was probed at the MP4 level, but the QCISD method was also used with the largest basis sets. While electron correlation favors 3 over 1 by about 2 kcal/mol, the correlated relative energies with all basis sets employed range from 0.36–1.03 kcal/mol in favor of 1 . The best estimate of this difference, 0.86 kcal/mol, is essentially identical with the (scaled) zero-point energy difference, 0.84 kcal/mol, favoring 3 over 1 . These results indicate that 1 and 3 have almost exactly the same energy at 0 K. Our best value for the dissociation energy of CH is 42.0 kcal/mol [QCISD(T)/6-311 + + G(3df, 3pd)//MP2(fu)/6-311 + + G(2df, 2pd), corrected to 298 K], which agrees very well with the experimental value. © 1992 by John Wiley & Sons, Inc. 相似文献
7.
Thomas Bally Helmut Baumgrtel Ulrich Büchler Edwin Haselbach Wolfgang Lohr John P. Maier Jürgen Vogt 《Helvetica chimica acta》1978,61(2):741-753
The enthalpy of formation of tris(methylidene)-cyclopropane (“[3]radialene”, 1 ) has been determined as ΔH = 396 ± 12 kJ mol?1 from three fragmentation reactions of its molecular ion 1 + formed from 1 by photoionisation using synchrotron radiation. Comparative electron impact measurements using conventional mass spectrometry were also performed. A treatment of the latter data is described which leads to satisfactory agreement with the photoionization data. The experimental value of ΔH( 1 ) is compared with various theoretical estimates. The strain energy of 1 is calculated to be 226.3 kJ mol?1. Linear extrapolation of this quantity from the increase of strain in passing from cyclopropane to methylidenecyclopropane yields 282.4 kJ mol?1. The discrepancy between these values, already predicted by Dewar and Baird ten years ago from theoretical calculations, is discussed on the basis of maximum overlap considerations. The enthalpy of formation of bis(methylidene)cyclopropane is predicted to be ΔH= 309 kJ mol?1. 相似文献
8.
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
9.
The haloacetyl ions [XCH2CO+], X = Cl, Br, I, have been produced by the dissociative ionization of selected precursor molecules and identified via their fragmentation characteristics. Their heats of formation, Δ, were 708 ± 8, 750 ± 25 and 784 ± 10 kJ mol?1, respectively, all appreciably above ΔH for [CH3CO+], 653 kJ mol?1. The effect of halogen substitution α to carbonyl is discussed for neutral molecules and their molecular ions. 相似文献
10.
H. Donald B. Jenkins Luminita C. Jitariu Ingo Krossing Jack Passmore Reijo Suontamo 《Journal of computational chemistry》2000,21(3):218-226
The dimerization energies of two M to give M (M=S,Se) were calculated. They depend strongly on the size of the basis set and the correlation method used (ranging from 217 to 522 kJ/mol, M = S) and, therefore, a systematic study of basis set and correlation effects was performed [MP2, MP3, MP4(SDQ), CCSD, CCSD(T)]. The introduction of a second set of polarising d‐functions caused a significant reduction of the dimerization energies, but neither of the above limits is reached by the MPn (n=2,3,4) theory, even with the largest basis sets [cc‐pVQZ]. However, convergence was achieved by CCSD(T), compound methods or hybrid HF/DFT calculations employing flexible basis sets [e.g., CCSD(T)/cc‐pV5Z, CBS‐Q or B3PW91/6‐311+G(3df)] and revealed an average dimerization energy of 261 (199) kJ/mol for sulfur (selenium), ΔrH298 (2S → S) is 257 kJ/mol. In the selenium system the dependence on basis set and correlated method was less pronounced. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 218–226, 2000 相似文献
11.
Mikhail N. Glukhovtsev Paul Von Ragu Schleyer 《International journal of quantum chemistry》1993,46(1):119-125
The lowest-energy N4 is computed ab initio to be the planar C2h(3Bu) open-chain structure 13 . The open-chain N4 singlet-state structures dissociate on geometry optimization. The tetraazatetrahedrane Td structure 1 and the tetrazete D2h structure 2 are minima at MP 2/6-31G *. However, both are higher in energy than 13 (24.1 and 21.2 Kcal/mol [UQCISD ) (T )(full)/6-311+G *//MP 2/6-31G * + ZPE (MP 2/6-31G )*, respectively]. The energy of 13 is 157.5 kcal/mol higher than that of two N2(1∑ molecules [UQCISD (T )(Full)/6-311+G *//MP 2/6-31G *] © 1993 John Wiley & Sons, Inc. 相似文献
12.
The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949–1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected C5? C6 bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 1016.0±0.3 exp(?300.4 ± 12.6 kJ mol?1/RT) s?1 for bond fission and 1013.2+0.4 exp(?247.7 ± 8.4 kJ mol?1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔH [H2CCHCC?H2] = 391.9, DH [H2CCHCCCH2? H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol?1 for the 3-ethenylpropargyl radical, based on a value of 420.2 kJ mol?1 for the primary C? H bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol?1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH2?CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc. 相似文献
13.
Ana Filipa L.O.M. Santos Manuel A.V. Ribeiro da Silva 《The Journal of chemical thermodynamics》2010,42(12):1441-1450
The standard molar enthalpies of formation, in the crystalline phase, of three halogenated 1-phenylpyrrole derivatives, namely 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were derived from the respective enthalpies of combustion, measured by rotating-bomb combustion calorimetry. Their enthalpies of sublimation, at T = 298.15 K, were obtained from the Knudsen mass-loss effusion technique. From these two experimental parameters, the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 1-(4-fluorophenyl)pyrrole, 1-(4-chlorophenyl)pyrrole, and 1-(4-iodophenyl)pyrrole were calculated, respectively, as (26.2 ± 2.4) kJ · mol−1, (196.2 ± 2.5) kJ · mol−1, and (311.5 ± 2.4) kJ · mol−1.The gas-phase enthalpies of formation of both fluorine and chlorine compounds were estimated by G3(MP2)//B3LYP computations. For the iodine compound, the B3LYP/6-311G(d):ECP46MDF approach was employed. Additionally, the DFT calculations were extended to estimate the enthalpy of formation of the bromine derivative, 1-(4-bromophenyl)pyrrole, performed at the B3LYP/6-311G(d) level of theory. 相似文献
14.
Introduction A series of lanthanide sulfide complexes have beenlargely used for ceramics and thin film materials1 andthese complexes could be prepared from the precursorswhich are the compounds containing lanthanide-sulfurbonds.2-4 For instance, the compounds synthesized with[(alkyl)2dtc]-, phen?H2O and lanthanide salts were usedas the volatile precursors for preparing lanthanide sul-fide, its friction properties in lubricant was investigatedin literature 5 and the preparation and propertie… 相似文献
15.
The two possible conformations of 13-R-substituted oxyprotoberberines are enantiomeric. The racemization barriers are determined for three of these compounds (R=OMe, OCOMe, OCOPh) using variable temperature 1H NMR. It was found that ΔG = 39.0 kJ mol?1 when R = OMe, ΔG = 63.5 kJ mol?1 when R = OCOMe and ΔG = 63.7 kJ mol?1 when R = OCOPh. When R = H, however, the barrier is well below 35 kJ mol?1, suggesting that one of the factors influencing these racemization barriers (as in 2,2′-bridged biphenyl systems) is steric in origin. Such low barriers to racemization do not allow easy handling of the enantiomers after resolution, but could allow better complexation of the one desired enantiomer to the receptor. 相似文献
16.
F. P. Emmenegger 《无机化学与普通化学杂志》1987,545(2):56-68
The equilibrium constants of the reactions MBr2(s) + Al2Br6(sln) ? MAl2Br8(sln) M = Cr, Mn, Co, Ni, Zn, Cd have been measured at 298 K in toluene. Ni: 0.017 ± 0.0024, Co: 0.54 ± 0.07, Zn: 1.5 ± 0.2, Mn: 2.1 ± 0, 7, Cr: 2.2 ± 1, Cd: 7 ± 5. They are compared with literature values of the equilibrium constants of analogous reactions in the gas phase MX2(s) + Al2X6(g) ? MAl2X8(g), X = Cl, Br. For CoAl2Br8(sln) the temperature dependence of the equilibrium constant yielded ΔfH = ?9.4 ± 1 kJ mol?1 and ΔfS = ?39.5 ± 3 J mol?1 K?1 while literature values for CoAl2Br8(g) are ΔfH = 42.4 ± 2 kJ mol?1 and ΔfS = 42.9 ± 2 J mol?1 K?1. The solubility of Al2Br6 in toluene as well as its enthalpy of dissolution have been measured in order to evaluate ΔH° and ΔS° of the solvation of Al2Br6(g) and CoAl2Br8(g) in toluene by a thermodynamic cycle. Solvation of Al2Br6(g): ΔH = ?72.7 ± 1 kJ mol?1, ΔS = ?139.6 ± 4 J mol?1 K?1, solvation of CoAl2Br8(g): ΔH = ?124.5 ± 4kJ mol?1, ΔS = ?222 ± 9J mol?1 K?1. Thus, CoAl2Br8 interacts more strongly with the solvent toluene than Al2Br6 does. 相似文献
17.
The interaction of the palladium(II) complex [Pd(hzpy)(H2O)2]2+, where hzpy is 2‐hydrazinopyridine, with purine nucleoside adenosine 5′‐monophosphate (5′‐AMP) was studied kinetically under pseudo‐first‐order conditions, using stopped‐flow techniques. The reaction was found to take place in two consecutive reaction steps, which are both dependent on the actual 5′‐AMP concentration. The activation parameters for the two reaction steps, i.e. ΔH = 32 ±2 kJ mol?1, ΔS = ?168 ±7 J K?1 mol?1, and ΔH = 28 ± 1 kJ mol?1, ΔS = ?126 ± 5 J K?1 mol?1, respectively, were evaluated and suggested an associative mode of activation for both substitution processes. The stability constants and the associated speciation diagram of the complexes were also determined potentiometrically. The isolated solid complex was characterized by C, H, and N elemental analyses, IR, magnetic, and molar conductance measurements. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 132–142, 2010 相似文献
18.
Tianfang Wang Hayley J. Andreazza Daniel Bilusich John H. Bowie 《Rapid communications in mass spectrometry : RCM》2009,23(11):1669-1677
The characteristic fragmentations of a pTyr group in the negative ion electrospray mass spectrum of the [M–H]? anion of a peptide or protein involve the formation of PO (m/z 79) and the corresponding [(M‐H)?–HPO3]? species. In some tetrapeptides where pTyr is the third residue, these characteristic anion fragmentations are accompanied by ions corresponding to H2PO and [(M‐H)?–H3PO4]? (these are fragmentations normally indicating the presence of pSer or pThr). These product ions are formed by rearrangement processes which involve initial nucleophilic attack of a C‐terminal ‐CO [or ‐C(?NH)O?] group at the phosphorus of the Tyr side chain [an SN2(P) reaction]. The rearrangement reactions have been studied by ab initio calculations at the HF/6‐31+G(d)//AM1 level of theory. The study suggests the possibility of two processes following the initial SN2(P) reaction. In the rearrangement (involving a C‐terminal carboxylate anion) with the lower energy reaction profile, the formation of the H2PO and [(M‐H)?–H3PO4]? anions is endothermic by 180 and 318 kJ mol?1, respectively, with a maximum barrier (to a transition state) of 229 kJ mol?1. The energy required to form H2PO by this rearrangement process is (i) more than that necessary to effect the characteristic formation of PO from pTyr, but (ii) comparable with that required to effect the characteristic α, β and γ backbone cleavages of peptide negative ions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
The reactions of dimethyl ether (CH3OCH3, DME) with O(3P) and H atoms have been studied at high temperatures by using a shock tube apparatus coupled with atomic resonance absorption spectroscopy (ARAS). The rate coefficients for the reactions CH3OCH3 + O(3P) → CH3OCH2 + OH (1) and CH3OCH3 + H → CH3OCH2 + H2 (2) were experimentally determined from the decay of O(3P) and H atoms as: These results show that DME can react with O(3P) atoms more easily than with H atoms. By combining these results with the previous lower temperature data, we obtained the following modified Arrhenius expressions applied over the wide temperature range between 300 and 1500 K: Both reactions of DME are faster than those of ethane, because the dissociation energy of the C? H bond in DME is smaller. Furthermore, the rate coefficients for reactions ( 1 ) and ( 2 ) were calculated with the transition‐state theory (TST). Structural parameters and vibrational frequencies of the reactants and the transition states required for the TST calculation were obtained from the MP2(full)/6‐31G(d) ab initio molecular orbital (MO) calculation. The energy barrier, E?0, was adjusted until the TST rate coefficient most closely matched the observed one. The fitting results of E(1) = 23 kJ mol?1 and E(2) = 34 kJ mol?1 were in agreement with the G2 energy barriers, within the expected uncertainty, demonstrating that the experimentally determined rate coefficients were theoretically valid. © 2006 Wiley Periodicals, Inc. 39: 97–108, 2007 相似文献
20.
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 ΔG≠218 = 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