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1989 (196)
61Author    VernonJ. Shiner, ThomasE. NeumannRequires cookie*
 Title     
 Abstract    r o tiu m -D e u te r iu m F r a c tio n a tio n F a c to r s fo r O r g a n ic M o le c u le s C a lc u la te d F ro m V ib r a tio n a l F o rc e F ie ld s This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday New valence force fields have been calculated for forty-seven small organic molecules and used to calculate protium-deuterium fractionation factors. Factors for molecules of the type CH ,X and HCOX have been found to correlate with the electronegativities of X and the CX bond lengths. The effects of cumulative substitution on a given C atom on the alpha CH fractionation factors have been examined. Some uses of the factors in mechanistic analysis are discussed. 
  Reference    Z. Naturforsch. 44a, 337—354 (1989); received February 6 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0337 
 Volume    44 
62Author    Katalin Tóth, Gabor JancsóRequires cookie*
 Title     
 Abstract    p p lic a tio n o f V a p o r P r e s s u r e I s o to p e E f fe c t to th e D e te rm in a tio n o f V ib r a tio n a l A n h a rm o n ic ity in th e L iq u id P h a s e Dedicated to Professor Jac ob Bigeleisen on the occasion of his 70th birthday The experimentally observed H/D vapor pressure isotope effects in chloroform and bromoform were combined with reliable spectroscopic data from the literature in order to obtain information on the change of the potential curve of the CH stretching motion on vapor-liquid transition. The parameters studied include the Morse potential parameters, the anharmonicity constant and the harmonic, cubic and quartic force constants in both phases. While the anharmonic character of the potential energy curve of the CH oscillator of chloroform has been found to decrease on condensa­ tion. the opposite behavior has been observed in the case of bromoform. 
  Reference    Z. Naturforsch. 44a, 355 (1989); received December 30 1988 
  Published    1989 
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 Identifier    ZNA-1989-44a-0355 
 Volume    44 
63Author    Tseng-Ven King, Takao Oi, Anthony Popowicz, Karl Heinzinger, Takanobu IshidaRequires cookie*
 Title     
 Abstract    a p o r P r e s s u r e I s o to p e E ffe c ts in L iq u id a n d S o lid A m m o n ia Dedicated to Professor Jacob Bigeleisen on the occasion of his 70tli birthday The H/D and 14N/15N vapor pressure isotope effects in liquid and solid ammonia have been measured at temperatures between 163 K and 243 K. The isotopic vapor pressure data have been fitted to T ln (P' P) = A/T-B for the liquid/liquid, liquid/solid and solid/solid ranges of temperature. The triple points are; 195.41 K (45.49 torr) for 14NH3, 198.96 K (48.35 torr) for 14ND3, and 195.58 K (48.83 torr) for 15NH3. The isotopic difference in the vapor pressures of NH3 and ND3 at temper­ atures between 195.41 K and 198.96 K is nearly independent of temperature within the present experimental uncertainty. The phase ratios of the reduced partition function ratios, / it,//gas and /soi//gas, deduced from these results are well represented by Tin (fc/fg) = A/T-B. Molecular forces in the liquid and solid ammonias are discussed using a simple cell and a 4-molecular unit cell model, respectively. The librational motions in the liquid are almost as highly hindered as they are in the solid, but the directionality of the external forces on nitrogen atoms in liquid ammonia is not as well defined as in the solid. 
  Reference    Z. Naturforsch. 44a, 359—370 (1989); received January 24 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0359 
 Volume    44 
64Author    MaryFoster Smith, W. Alexander, Van HookRequires cookie*
 Title     
 Abstract    o m e M e a s u r e m e n ts o f H / D P o la riz a b ility Is o to p e E f fe c ts U s in g D if fe r e n tia l R e f r a c to m e tr y Dedicated to Professor Jacob Bigeleisen on the occasion of his 70tli birthday Refractive index differences between the H and D isomers of some common molecules in the liquid phase were measured between 404.7 and 690.0 nm. The data are combined with information on molar volume isotope effects to yield values for H/D isotope effects on the static polarizability, the vibrational contribution to the static and frequency dependent parts of the polarizability, and the H/D isotope effect on the second moment of the electronic charge distribution. The present results suffice to demonstrate the practicability of this technique to measure the components of the polariz­ ability listed above. However for accurate resolution of the vibrational and second moment contri­ butions, refractive index data of still greater precision will be required. 
  Reference    Z. Naturforsch. 44a, 371—375 (1989); received January 17 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0371 
 Volume    44 
65Author    C. M. Stevens, A. F. WagnerRequires cookie*
 Title      
 Abstract    Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Kinetic isotopic fractionation plays an important role in the quantitative analysis by isotopic studies of the cycles of the two atmospheric trace gases, CO and CH4, which are important because of their impact on the environment. These gases are scavenged from the atmosphere mainly by homogeneous gas phase oxidation reactions with OH radicals. The isotopic composition of these gases provides constraints on the relative distribution of the fluxes from sources, natural or anthro­ pogenic, of different isotopic compositions. The relationship between the composition of the gas in the atmosphere and the average value of the sources is determined by the fractionation effect of the scavenging processes, in particular the reaction with OH. Thus, knowledge of the fractionation effect is essential to determining the relative distribution of the fluxes from isotopically different sources. The reactions CO + OH and CH4 + OH exhibit several types of KIE's including normal, inverse, and compound effects resulting from the bimodal character of the former. A brief discussion of the measured values of the KIE for these reactions and their application to interpretation of the atmospheric cycles of CO and CH4 is presented. 
  Reference    Z. Naturforsch. 44a, 376 (1989); received February 3 1989 
  Published    1989 
  Keywords    Kinetic isotopic fractionation, CO + OH, CH4 + OH, Atmospheric carbon monoxide, Atmospheric methane 
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 Identifier    ZNA-1989-44a-0376 
 Volume    44 
66Author    CharlesL. Kneifel, HaroldL. Friedman, MarshallD. NewtonRequires cookie*
 Title     
 Abstract    a lc u la tio n o f th e T h e rm o d y n a m ic S o lv e n t I s o to p e E f fe c t f o r F e r r o u s a n d F e r ric Io n s in W a te r Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Molecular dynamics simulations of molecular models of Fe2 + and Fe3+ in water (L20 = H20 or D20) are used to generate various correlation functions that characterize the respective hexaaquo hydration complexes. The static Fe2+-oxygen and Fe2+-hydrogen correlation functions are compared in detail with the first difference neutron diffraction results of Enderby et al. for Ni2 + . Velocity autocorrelation functions and corresponding power spectra are generated and analyzed for those modes of hydration shell water molecules whose reduced masses are most sensitive to the changes from H20 to D20. Various approximations are applied to these data to calculate the solvent isotope effect on the difference in hydration free energies for Fe2+ and Fe3 + . These different approximations all lead to the qualitative conclusion that the net solvent isotope effect reflects a large degree of cancellation between the OL stretching modes and the librational modes. The simulation results generally agree with the results of earlier quantum chemical calculations applied to the same system, but in some respects the new results are not as realistic as the earlier ones. It is proposed that the agreement with experiment would be improved by changes in the model potential which are motivated by other, independent considerations. 
  Reference    Z. Naturforsch. 44a, 385 (1989); received February 12 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0385 
 Volume    44 
67Author    Y. Fujii, M. Nomura, M. Okamoto, H. Onitsuka, F. Kawakami, K. TakedaRequires cookie*
 Title     
 Abstract    n A n o m a lo u s Is o to p e E ffe c t o f 235U in U (I V) -U (V I) C h e m ic a l E x c h a n g e Dedicated to Professor J. Bigeleisen on the occasion of his 70th birthday The abundance ratios of 234U, 235U, 236U and 238U were determined by mass spectrometry on uranium samples obtained from a chromatographic uranium enrichment process based on the U(IV) — U(VI) chemical exchange reaction. According to standard theory, the elementary isotope effect in processes based on equilibrium chemical exchange is proportional to the mass difference of the isotopes. In the present work this has been confirmed for 234U, 236U and 238U. However, according to the observed data the fractionation between 234U and 235U is much smaller than the one between 235U and 236U in spite of the same mass difference in either isotopic pair. The anomaly of the fractionation is concluded to be due to the characteristics of 235U, which is the only odd mass number isotope in the present system. 
  Reference    Z. Naturforsch. 44a, 395 (1989); received January 17 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0395 
 Volume    44 
68Author    Takao Oi, Hidetake KakihanaRequires cookie*
 Title     
 Abstract    T h e o r e tic a l C o n s id e ra tio n on U r a n iu m Is o to p e E f fe c ts O b s e r v e d in C h e m ic a l U ra n iu m -2 3 5 E n r ic h m e n t P r o c e s s e s * This paper is dedicated to Professor J. Bigeleisen on the occasion oj his 70th birthday Theoretical consideration on the uranium isotope effects in chemical chromatographic uranium isotope enrichment processes are presented, making use of up-to-date spectroscopic, solution chem­ ical and separation factor data. It is shown that hydration of the uranyl (U02 +) and uranous (U4 +) ions has a profound effect on the reduced partition function ratios (RPFR's) of these ions and that, in accordance with experiment, the RPFR of the uranous ion is larger than that of the uranyl ion. Future prospects concerning the separation factors in chemical processes are mentioned. 
  Reference    Z. Naturforsch. 44a, 399—405 (1989); received December 30 1989 
  Published    1989 
  Keywords    Chemical processes for uranium isotope enrichment, Uranium isotope effects, Reduced partition function ratio, Separation factor, Uranyl and uranous ions 
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 Identifier    ZNA-1989-44a-0399 
 Volume    44 
69Author    Y. Chiang, A. J. Kresge, P. A. WalshRequires cookie*
 Title     
 Abstract    o m e K in e tic a n d E q u ilib riu m Is o to p e E ffe c ts in th e Is o b u ty lp h e n o n e E n o l a n d E n o la te Io n S y s te m This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday The following kinetic isotope effects were determined for acid-catalyzed ketonization of isobutyro-phenone enol and enolate ion through rate-determining hydron transfer from catalyst to substrate: enol, kH/kD = 3.30±0.07 (hydronium ion catalysis), /cH//cD = 4.0 + 2.8 (acetic acid catalysis); enolate ion, kH/kD= 1.00 + 0.21 (hydronium ion catalysis), kH/kD = 3A \ +0.20 (acetic acid catalysis), kH /kD = 7.48 + 0.23 (water catalysis). The magnitude of these isotope effects, when assessed in terms of the free energies of reaction for the processes in which they occur, are consistent with Melander-West-heimer-Bigeleisen theory. An equilibrium isotope effect of KH/KD = 5.88 + 0.32 was also determined for the ionization of isobutyrophenone enol as an oxygen acid. 
  Reference    Z. Naturforsch. 44a, 406—412 (1989); received November 18 1988 
  Published    1989 
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 Identifier    ZNA-1989-44a-0406 
 Volume    44 
70Author    L. Xie, W. H. SaundersRequires cookie*
 Title    Is  
 Abstract    o to p e E ffe c ts in K in e tic E n o la te F o r m a tio n fro m 2 -P e n ta n o n e a n d 2 -P e n t a n o n e -l , l , l -d 3 This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday 2-Pentanone and 2-pentanone-l,l,l-d3 were treated with three-fold excesses of lithium diiso-propylamide (LDA) or lithium hexamethyldisilazide (LHMDS) in tetrahydrofuran (THF) with and without hexamethylphosphoric triamide (HMPA, 3 mol per mol of base) at temperatures ranging from 24 to — 70 °C. The deuterium kinetic isotope effects calculated from the product ratios (mea­ sured by GLC as trimethylsilyl enol ethers) showed a range of temperature dependences: none (LDA in THF), attenuated with A^jA^ = 2.53 (LHMDS in THF), and normal with /1H//1D~0.6 indicating moderate tunneling (LDA and LHMDS in THF-HMPA). The variation in temperature dependence is attributed to reaction via multiple base species in which HMPA affects the equilibria between the base species. 
  Reference    Z. Naturforsch. 44a, 413 (1989); received January 13 1989 
  Published    1989 
  Keywords    Isotope Effects, Kinetic Enolates, Temperature Dependence, Lithium Dialkylamide Bases 
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 Identifier    ZNA-1989-44a-0413 
 Volume    44 
71Author    MauriceM. Kreevoy, In-Sook, Han LeeRequires cookie*
 Title      
 Abstract    Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday If hydride transfer from a donor, A^H, to an acceptor, A,+ , involves tunneling, phenomenological theory suggests a characteristic functional relation between rate constants and the equilibrium constant, i.e. between ln (ktj H/ktj d) and In Kjj. Tunneling occurs at a heavy atom separation larger than that of the transition state (saddle point). This gives the critical configuration (point of no-re-turn) for H-transfer a larger heavy atom separation than that for D-transfer and leads to the pattern described through a corollary of Marcus theory of atom transfer. The theory is called corner-cutting because it shortens the path which represents the reaction in multi-dimensional potential energy space. If the reactions are moderately spontaneous and the variation in structure which generates the variation in ktj H, ku D and K(j is in the acceptor, the slope of the plot of ln (ku H/kij. d) against ln Kij is expected to be negative; if the structure variation is in the donor it is expected to be positive. Similar results are expected for proton and hydrogen atom transfer. This behavior has now been observed, for hydride transfer between various nitrogen heterocycles (all of which may be regarded as analogues of the enzymatic cofactor, NAD"). These reactions have ktj ii/Tc.j [) ~~ 5. The increase of ktj H/ktj D, with increasing Ku, reported in this paper, is particularly hard to explain without corner-cutting. The present results, therefore, support the view that some tunneling is involved in most hydrogen transfer reactions, even when no anomalies are obvious. 
  Reference    Z. Naturforsch. 44a, 418 (1989); received January 11 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0418 
 Volume    44 
72Author    GillianC. Lynch, Philippe Halvick, DonaldG. Truhlar, BruceC. Garrett, DavidW. Schwenke, DonaldJ. KouriRequires cookie*
 Title     
 Abstract    e m ic la s s ic a l a n d Q u a n tu m M e c h a n ic a l C a lc u la tio n s o f Is o to p ic K in e tic B ra n c h in g R a tio s f o r th e R e a c tio n o f 0 (3P) w ith H D Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Tunneling probabilities for the reactions O + HD ->OH + D and O + DH ->OD + H have been calculated by semiclassical dynamical methods and compared to accurate quantal calculations for the same potential energy surface. The results are used to test the reliability of variational transition state theory with the least-action semiclassical method for tunneling probabilities for the prediction of intramolecular kinetic isotope effects. 
  Reference    Z. Naturforsch. 44a, 427—434 (1989); received January 13 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0427 
 Volume    44 
73Author    S. K. Bhattacharya, M. H. ThiemensRequires cookie*
 Title      
 Abstract    This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday The isotopic fractionation associated with the O + CO reaction has been studied using oxygen atoms produced by room temperature 0 2 photolysis at two different wavelengths, 185 and 130 nm. A large mass-independent isotopic fractionation is observed in the product C 02, extending the range of this type of reaction beyond 0 + 0 2 and SF5 + SF5. Kinetic evaluation of the data restricts the source of the mass-independent fractionation mecha­ nism to the O + CO recombination step rather than 0 2 photolysis, secondary ozone formation, or 0 2 photodissociation. At least one, and most likely two other fractionation processes appear to occur in the experiments, and interpretation of the isotopic results is tentative at present. Based on the relevant reaction rates and the value for the reduced partition function for isotopic exchange between O and CO, it is suggested that this process may occur prior to the < 5170 = <5180 recombi­ nation process. Secondary C02 photolysis may superimpose an additional fractionation. The exper­ imental data are also examined in the context of a model based upon energy randomization rates versus the lifetime of the activated complex. 
  Reference    Z. Naturforsch. 44a, 435—444 (1989); received April 24 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0435 
 Volume    44 
74Author    W.Wallace ClelandRequires cookie*
 Title      
 Abstract    Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday When a presteady state burst is seen in an enzymatic reaction where a change in absorbance accompanies the isotope-sensitive step, there will be an isotope effect on the initial rate of the burst. The apparent commitment which reduces the size of the intrinsic isotope effect will not be solely the partition ratio of the intermediate undergoing the isotope-sensitive step (as in steady state kinetics), but will also be a function of the ratio of the forward rate constants for the isotope-sensitive step and the one preceding it. A contour map of these relationships is presented. 
  Reference    Z. Naturforsch. 44a, 445 (1989); received November 14 1988 
  Published    1989 
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 Identifier    ZNA-1989-44a-0445 
 Volume    44 
75Author    M. A. Morgenstern, R. L. SchowenRequires cookie*
 Title     
 Abstract    re d ic tio n o f Iso to p e E ffe c ts fo r A n tic ip a te d I n te r m e d ia te S tr u c tu r e s in th e C o u rs e o f B a c te ria l D e n itrific a tio n This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Vibrational-analysis methods have been used to estimate the equilibrium 14N/15N isotope effects to be expected for conversion of nitrite anion to thirteen possible intermediate-state and product-state structures [HONO, NO + , NO, NO",*NO] in the reduction of nitrite ion to nitrous oxide denitrifying bacteria. The results, taken in combination with previous experimental isotope-effect and tracer studies of the Pseudomonas stutzeri and related systems, are consistent with a suggestion that a second nitrite anion enters the enzyme-catalytic cycle at the stage of a nitrosyl-ion intermediate but re-emerges after entry of the reducing electrons; the product nitrous oxide is then formed by disproportionation of enzymically generated hyponitrous acid. The calculations are consistent with contributions, under different experimental conditions, of several different transition states to limit­ ing the rate of the enzymic reaction. These transition states (and the corresponding experimental conditions) are the transition states for N —O fission in the generation of a mononitrogen elec-trophilic species from nitrite anion (high reductant, high nitrite concentrations), for attack of nitrite on this electrophile (high reductant, low nitrite concentrations) and for electron transfer to a dinitrogen-trioxide-like species (low reductant concentration). 
  Reference    Z. Naturforsch. 44a, 450 (1989); received January 10 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0450 
 Volume    44 
76Author    Hans-Heinrich Limbach, Ludger Meschede, Gerd SchererRequires cookie*
 Title      
 Abstract    tr a ta g e m s f o r th e S tu d y o f M u ltip le K in e tic H y d r o g e n /D e u te r iu m I s o to p e E f fe c ts o f P r o to n E x c h a n g e . E x a m p le : D i-p -f lu o r o p h e n y lf o r m a m id in e /T H F Dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Stratagems are presented for the determination of kinetic isotope effects of proton exchange reactions by dynamic NMR spectroscopy. In such experiments, lineshape analyses and/or polariza­ tion transfer experiments are performed on the exchanging protons or deuterons as well as on remote spins, as a function of the deuterium fraction in the mobile proton sites. These methods are NMR analogs of previous proton inventory techniques involving classical kinetic methods. A theory is developed in order to derive the kinetic isotope effects as well as the number of transferred protons from the experimental NMR spectra. The technique is then applied to the problem of proton exchange in the system 15N,15N'-di-p-fluorophenylibrmamidine, a nitrogen analog of formic acid, dissolved in tetrahydrofuran-d8 (THF). DFFA forms two conformers in THF to which s-trans and s-cis structures have been assigned. Only the s-trans conformer is able to dimerize and exchange protons. Lineshape simulations and magnetization transfer experiments were carried out at 189,2 K, at a concentration of 0.02 mol l-1, as a function of the deuterium fraction D in the 'H-15N sites. Using 1H NM R spectroscopy, a linear dependence of the inverse proton lifetimes on D was observed. From this it was concluded that two protons are transported in the rate limiting step of the proton exchange. This result is expected for a double proton transfer in an s-trans dimer with a cyclic structure. The full kinetic HH/HD/DD isotope effects of 233:11:1 at 189 K were determined through 19F NMR experiments on the same samples. The deviation from the rule of geometric mean, although substantial, is much smaller than found in previous studies of intramolecular HH transfer reactions. Possible causes of this effect are discussed. Key words: NMR spectroscopy (dynamic), Proton exchange, Isotope effects (kinetic HH/HD/DD), Formamidine, Hydrogen bonding. 
  Reference    Z. Naturforsch. 44a, 459 (1989); received January 25. 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0459 
 Volume    44 
77Author    Peder Svensson, Nils-Äke Bergman, Per AhlbergRequires cookie*
 Title    Is A Theoretical Study using the Ab Initio STO -3G Potential Energy Surface  
 Abstract    o to p e E ffe c ts a n d C o n c e rte d T w o -H y d ro n -T r a n s f e r b e tw e e n F o rm a m id in e M o le c u le s Dedicated to Professor Jacob Bigeleisen on the occasion of his 70 th birthday With the intention to assist mechanistic studies of two-hydron-transfer reactions using lH/2H isotope effects we have carried out theoretical studies of the two-hydron-transfer reaction between formamidine molecules. The ab initio STO-3G potential energy surface has been calculated and all stationary points characterized by their force constant matrices. With this basis set the two hydrons are transferred concertedly and synchronously. The transition state (TS) has D2h symmetry. 'H/2H isotope effects were calculated using the Bebovib-IV program. Our results deviated from predictions made from common simple vibrational models. The isotope effects are dominated by the zero-point-energy contribution. The effect due to the stretching vibrations of the initial state is to a small extent counteracted by stretching of the TS. The bending vibrations appear to play a dominant role in reducing the magnitude of the isotope effect for the two-hydron-transfer reaction to a value expected for a one-hydron-transfer reaction. 
  Reference    Z. Naturforsch. 44a, 473—479 (1989); received May 18 1989 
  Published    1989 
  Keywords    Two-hydron-transfer, Formamidine, Ab initio, STO-3G, Isotope effects 
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 Identifier    ZNA-1989-44a-0473 
 Volume    44 
78Author    Martin Saunders, GaryW. ClineRequires cookie*
 Title     
 Abstract    a lc u la tio n o f E q u ilib riu m I s o to p e E f fe c ts in a C o n f o r m a t io n a l^ M o b ile C a r b o c a tio n Dedicated to Jacob Bigeleisen on the occasion of his 70 th birthday The rapid, degenerate 1,2-hydride shift in 2,3-dimethyl-2-butyl cation in stable solution in SbF5/ S02C1F was perturbed by deuterium and 13C leading to splittings observed by 13C NMR spectros­ copy over a range of temperatures. Accurate values for equilibrium isotope effects were obtained from these data. Theoretical calculations of the equilibrium isotope effects were performed using the Gaussian-86 program to obtain an optimized geometry and the Cartesian force constant matrix, followed by the program QUIVER which applies the Bigeleisen-Mayer method. When all of the conformers, which are in rapid equilibrium, were considered specifically, quite good agreement between theory and experiment was obtained. 
  Reference    Z. Naturforsch. 44a, 480—484 (1989); received January 23 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0480 
 Volume    44 
79Author    LiemX. Dang, Philippe Bopp, Max WolfsbergRequires cookie*
 Title     
 Abstract    v a lu a tio n o f Is o to p e E ffe c ts o n H e n r y 's L a w C o n s ta n ts by a M o le c u la r D y n a m ic s T e c h n iq u e Dedicated to our teacher, colleague, and friend Jacob Bigeleisen on the occasion of his 70th birthday Solute isotope effects on Henry's law constants of aqueous solutions of argon atoms, of helium atoms, and of nitrogen molecules are considered. A cell model is employed; the translational and rotational motions are treated in the first quantum approximation while the vibrational motion of nitrogen is fully treated (but assumed to be separable and harmonic). The required mean square forces (or equivalent frequency parameters) are evaluated by classical molecular dynamics calcula­ tions. 
  Reference    Z. Naturforsch. 44a, 485—491 (1989); received February 20 1989 
  Published    1989 
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 Identifier    ZNA-1989-44a-0485 
 Volume    44 
80Author    DerekP N Satchell, RosemaryS. SatchellRequires cookie*
 Title    Deuterium Isotope Effects on the Silver Ion-Promoted Hydrolyses of S,S-Diethvlacetals of p-Substituted Benzaldehydes  
 Abstract    This paper is dedicated to Professor Jacob Bigeleisen on the occasion of his 70th birthday Solvent deuterium isotope effects support the view that the p-N02 and p-Me derivatives of benzaldehyde S.S-diethyl-acetal undergo silver ion-promoted hydrolysis in water by different mechanisms. scheme common [3] for O.O-acetals in the presence of H30 + ions, while for the latter we suggested a bimolecular A2-type mechanism with one (or more) water molecules in the slow phase of step (3). The compound with R = H may be an intermediate case [1, 2j. Solvent deuterium isotope effects are sometimes helpful in distinguishing between reaction mechanisms in solution [4], Relatively few studies, however, have examined such isotope effects in systems involving metal ion-promotion or catalysis. No general pattern of behaviour has been established in the way that it has for H30 +-catalysed processes [4], We have now studied the effect of using D,0 in place of H20 on some of the results for two of these S,S-acetals: the p-Me and p-N02 compounds. 
  Reference    Z. Naturforsch. 44a, 492—493 (1989); received January 3 1989 
  Published    1989 
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 TEI-XML for    default:Reihe_A/44/ZNA-1989-44a-0492_n.pdf 
 Identifier    ZNA-1989-44a-0492_n 
 Volume    44 
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