Deuterium isotope effects on the partial molal volumes of cyclohexane, acetone, and acetonitrile in carbon tetrachloride

Abstract

At 25°C both molar volumes V and partial molal volumes V: , , , in carbon tetrachloride of cyclohexane-dl? and of acetone-d6 are smallerthan V and V: C14 of the corresponding protio compounds. However, both V and V: , , , of acetonitrile-d, are larger than V and v&.,~ of acetonitrile-h3, and in solvent cyclohexane V:h,,12 of acetone-& and of acetone-h6 are approximately equal.Apparently deuteration has not only a steric effect, but (in polar compounds) a counter-balancing effect, which may be polar.G. RONALD BROWN, JULIAN K. EDWARD et JOHN T. EDWARD. Can. J. Chem. 61, 2684 (1983.A 25"C, les volumes molaires V et les volumesmolaires partiels V: , , , du cyclohexane-dl, et de I'acCtone-d6 dans le tCtrachlorur_e de carbone sont plus faibles que V et v:,,~ des composts non deuttrks correspondants. Cependant, les valeurs de V et de v :~~~ de I'acCtonitrile-d-, sont plusgrandes que les valeurs correspondantes pour I'acCtonitrile non deutCrt; dans le cyclohexane comme solvant, les valeurs de v:,,,,~ de l'acttone-d6 et de I'acttone-h6 sont a peu pres Cgales. Apparemment, la deutCration n'a pas seulement un effet stCrique, mais (dans les composCs polaires) un effet contre balan~ant qui peut &tre polaire.[Traduit par le journal]A large number of examples of secondary deuterium isotope effects on reaction rates (reviewed in refs. 1-3) has been observed. One explanation which accounts for many results depends on the idea that protio-alkyl groups (such as CH,) occupy a slightly larger volume than the corresponding deuteroalkyl groups (such as CD,), because of the greater amplitude of the zero-point vibration of the C-H as compared with the C-D bond. This idea finds support in the studies of Baldry and Robinson (4) on the conformational equilibrium of trans-lmethyl-d,-3-methylcyclohexane, which showed the conformation having CD, axial favoured by 11 cal mol-' over the conformation having CH3 axial; in optical rotatory dispersion studies of Djerassi and co-workers (5); and in studies of steric effects of H and D on ' H and I3C chemical shifts by Anet and Dekmezian (6).However, the most direct indication of this volume difference might be expected to come from measurements of molar volumes. Indeed, at the triple point (7) and at the critical temperature (8) the molar volume V of CH, is greater than that of CD,. Similarly, at ordinary temperatures the molar volumes of benzene (9-1 l ) , cyclohexane (16), and toluene (1 1) are greater than the volumes of their deuterated forms. However, Rabinovich (1 1) repcrted that the molar volumes of CDCl3, CD3N02, PhND?, C H 3 0 D , CH3CH20D, CH,CH2CH20D, (CH3)?CHOD, CH3CH2CH2CH20D, CH20D-CH20D, CH20D-CHOD-CH20D, and (CH,),CCO,D were greater than the volumes of the corresponding protio compounds.This last result pointed to a curious difference between hydrocarbons and more polar organic molecules which we thought worth confirming, particularly since it was based on density measurements made with pyknometers, which are probably less accurate than the direct-reading density meters now availabl...

Deuterium isotope differences in 2-propanone, (CH3)2CO/(CD3)2CO: a high-pressure sound-speed, density, and heat capacities study

“…A simple core-size analysis tell us that the molecular volume of acetoneh 6 is expected to be slightly greater than that of acetone-d 6 as anharmonicity, combined with higher internal vibrational frequencies for the lighter molecule, lead to greater vibrational amplitudes of the C-H stretching modes compared to the C-D ones. The difference in the bond length between the C-H and the C-D bond is $0.0005 nm [4,10]. For instance, in ethane, r CH = 0.1112 nm and r CD = 0.1107 nm.…”

“…In this work, we report extensive data of several thermophysical properties of acetone-d 6 in broad temperature and pressure ranges, which when combined with those of acetone-h 6 , permit us to test the reliability of a simple statistical-mechanics approach for heat capacitiy isotope effects. Unfortunately, in contrast to the situation encountered regarding many other properties, there is not, to date, a well-established theory for molar volume isotope effects [2][3][4][5][6][7][8][9][10][11][12]. The rather murky procedure of establishing links between molecular structure and density combined with the lack of extensive (and accurate) data on the molar density shifts upon isotopic substitution are the responsible factors.…”

“…The latter properties have been investigated over considerable temperature and pressure ranges. Brown [4] reported on the molar volume IE of acetone at 298 K and 0.1 MPa, while Ibberson et al [5] determined calorimetrically the isobaric specific heat capacity IE in the temperature range (10 to 300) K and 0.1 MPa.…”

On the Determination of Partial Molar Polarizations and Dipole Moments of Solutes from Multicomponent Solutions Alone: Experimental and Model Development Using Deutero-Labeled Organic Compounds

“…c Toluene- h 8 in cyclohexane calculated at x i = 0.0589, ref . d Acetone- d 6 in cyclohexane, ref . e Acetone- h 6 in cyclohexane, ref .…”

Deuterium isotope effect on molar heat capacities and apparent molar heat capacities in dilute aqueous solutions: A multi-channel heat-flow microcalorimeter study

“…Indeed, deuterium isotope effects on several physico-chemical properties have been previously reported and discussed [5][6][7][8][9][10][11][12][13][14][15][16]. Depending on the nature of the physico-chemical properties, deuterium isotope effects can be quite significant to nearly negligible.…”