Thermodynamic parameters of deuterated and tritiated nonlinear triatomic hydrides

Entropy and free energy are calculated for isotopic forms of H₂S and H₂Se in the ideal-gas state.     

Vibrational relaxation of normal and deuterated liquid nitromethane

Anti-Stokes Raman scattering is used to monitor vibrational energy redistribution in the ambient temperature liquids nitromethane (NM-h3) and perdeuterated nitromethane (NM-d3) after ultrafast IR excitation of either the symmetric or asymmetric CH- or CD-stretch transitions. The instantaneous populations of most of the fifteen NM vibrations are determined with good accuracy, and a global fitting procedure with a master equation is used to fit all the data. The pump pulses excite not only CH- or CD-stretches but also certain combinations of bending and nitro stretching fundamentals. The coupled vibrations that comprise the initial state are revealed via the instantaneous rise of the anti-Stokes transients associated with each vibrational fundamental. In contrast to many other polyatomic liquids studied previously, there is little energy exchange among the CH-stretch (or CD-stretch) excitations, which is attributed to the nearly free rotation of the methyl group in NM. The vibrational cooling process, which is the multistep return to a thermalized state, occurs in three stages in both NM-h3 and NM-d3. In the first stage, the parent CH- or CD-stretch decays in a few picoseconds, exciting all lower-energy vibrations. In the second stage, the midrange vibrations decay in 10-15 ps, exciting the lower-energy vibrations. In the third stage, these lower-energy vibrations decay into the bath in tens of picoseconds. The initial excitations are thermalized in approximately 150 ps in NM-h3 and there is little dependence on which CH-stretch is excited. VC is somewhat faster in NM-d3 with more dependence on the initial CD-stretch, taking approximately 100 ps with symmetric CD-stretch excitation and approximately 120 ps with asymmetric CD-stretch excitation. Comparison is made with earlier nonequilibrium molecular dynamics simulations of VC [Kabadi, V. N.; Rice, B. M. Molecular dynamics simulations of normal mode vibrational energy transfer in liquid nitromethane. J. Phys. Chem. A 2004, 108, 532-540]. The simulations do a good job of reproducing the observed VC process and in addition they predicted the slow interconversion among CH-stretch excitations and the slower relaxation of the asymmetric CH-stretch now observed here.     

Thermodynamic properties of mixtures of deuterated and undeuterated dipalmitoyl phosphatidylcholines (differential scanning calorimetry/lipid bilayers/membranes)

In need for nonperturbing but spectroscopically unique environments for studies of lipid/lipid and lipid/protein interactions, we have investigated the thermodynamic properties of deuterated and undeuterated dipalmitoyl phosphatidylcholines as well as the mixtures of both. The data have been collected using the highly sensitive differential scanning calorimetry. From the results of these measurements we conclude that mixtures of deuterated and undeuterated lipids behave ideally. The transition enthalpies, transition entropies and the cooperative unit are given as a function of the input ratio of the components and the phase diagram is constructed, showing that the deuterated lipids are suitable as nonperturbing probes.     

Synthesis and properties of a deuterated phenolic resin

A highly deuterated novolac‐type phenolic resin was prepared by polycondensation of deuterated phenol and formaldehyde using oxalic acid as an acid catalyst. The polycondensation of deuterated monomers and the formation of the highly deuterated phenolic resin were confirmed by the gel permeation chromatography, IR, and ¹H NMR analyses. With the exception of hydroxyl groups, the degree of deuteration was estimated to be more than 98%. The polymer conformation in THF solution was evaluated by the scaling exponent of the Mark–Houwink–Sakurada equation. The exponent of the deuterated phenolic resin is 0.26 in THF at 40 °C and is close to that of a nondeuterated phenolic resin, which suggests that phenolic resins behave like a compact sphere irrespective of deuteration. The curing behavior of the deuterated phenolic resin with hexamethylenetetramine was confirmed by differential scanning calorimetry analysis. The cured highly deuterated phenolic resin exhibits a lower incoherent neutron scattering background than that of the nondeuterated phenolic resin, which suggests that the former is suitable for matrix resins with low incoherent backgrounds for small‐angle neutron scattering studies of thermosetting resins. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Network properties of mixtures of protonated and deuterated polyethylene

Mixtures of protonated and deuterated polyethylene were irradiated in the melt. The degree of crystallinity, the degree of crosslinking, as well as the enthalpyH and the melting pointT _M were determined. No significant differences in the degree of crosslinking between protonated and deuterated chains were found. The mass specific entropyS of the uncrosslinked samples remained constant and independent of the deuterium concentration. For the crosslinked samples, a netpoint entropy was postulated. A weaker Van der Waals interaction could explain the decrease in melting temperature by deuteration (for weakly crosslinked samples).     

Rhodium-catalyzed hydroformylation of cyclopropenes

The first catalytic diastereo- and enantioselective hydroformylation of cyclopropenes was demonstrated. The reaction proceeds efficiently under very mild conditions and low catalyst loadings providing high yields of cyclopropylcarboxaldehydes. This novel methodology represents a convenient, atom-economic approach toward optically active cyclopropylcarboxaldehydes from readily available prochiral cyclopropenes.     

Vibrational spectra and normal coordinate analysis of p-cresol and its deuterated analogs

I.r. and Raman spectra of p-cresol and its seven deuterated analogs were investigated in dilute solutions of hydrophobic solvents. Assignments of the observed i.r. and Raman bands were made on the basis of isotopic frequency shifts, Raman polarization properties, i.r. intensifies and normal coordinate calculations. The calculated normal frequencies are in good agreement with the experimental ones: the average error below 1700 cm⁻¹ is 3.8 cm⁻¹ for 164 in-plane vibrations and 3.3 cm⁻¹ for 59 out-of-plane vibrations. The calculated vibrational modes may be useful in analysing the vibrational spectra of tyrosine. It is suggested that several doublets due to Fermi resonance and a trio of Raman bands in the 1260-1160 cm⁻¹ region are potential probes for the micro-environments of tyrosine side chains in proteins.     

Thermodynamic properties of hexacosane

The heat capacity of a purified sample of hexacosane, n-C₂₆H₅₄, has been measured from 13 to 358 K. The enthalpies of transition near 325.5 K and fusion at 329.25 K, and the purity of the sample have been determined; the accuracy of the results is influenced by the closeness in temperature, and overlap, of the crystal-to-crystal and crystal-to-liquid phase transitions. Thermodynamic properties have been calculated from the heat capacities and enthalpies.     

Synthesis and thermolysis of tetrasubstituted cyclopropenes

Photolysis of 5-benzyl-2-methoxy-2,5-dimethyl-³-1, 3,4-oxadiazoline and of the 5,5-dibenzyl analogue with 300-nm light afforded 1-phenyl-2-diazopropane and 1,3-diphenyl-2-diazopropane, respectively. The diazoalkanes were intercepted, in situ, with dimethyl acetylenedicarboxylate to afford 3-benzyl-4,5-bis(methoxycarbonyl)-3-methyl-3H-pyrazole and 3,3-dibenzyl-4,5-bis(methoxycarbonyl)-3H-pyrazole, respectively. Those pyrazoles are short-lived under the reaction conditions and undergo two major reactions. Photolysis prior to rearrangement affords the corresponding 3,3-dialkyI-1,2-bis(methoxycarbonyl)-cyclopropenes. Thermal 1,5-benzyl migration converts the two 3H-pyrazoles in part into the corresponding 4H-pyrazoles, which undergo photolysis to 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropenes.Thermolysis of the 3,3-dialkyl-1,2-bis(methoxycarbonyl) cyclopropenes affords conjugated dienes, presumably through the sequence cyclopropene vinyl carbene diene. The stereochemistry of the dienes was determined and a mechanism consistent with that stereochemistry is proposed.The 2,3-dialkyl-1,3-bis(methoxycarbonyl)cyclopropanes are very stable under conditions that convert isomeric 3,3-dialkyl-1,2-bis(methoxycarbonyl)cyclopropenes to conjugated dienes. It is proposed that the effect of substitution pattern on the thermolysis rate constants is the result of combined ground state and transition state factors.     

Thermodynamic properties of tetrachlorocyclopropene

A facility is described which incorporates the use of electronic microbalances to follow gravimetric changes due to the formation or spallation of surface oxides on metals or alloys during high temperature oxidation. The outputs from the balances are fed into a data acquisition system which allows easy collection and analysis of the data from more than one microbalance.The sensitivity of the technique is illustrated by reference to the measurements of oxidation and spallation on a 20Cr/25Ni/Nb stabilised stainless steel oxidised in flowing CO₂ based gas at 1 atmosphere pressure and 850°C.     

Thermodynamic properties of chloropinnoite

The molar enthalpies of solution of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O in approximately 1 mol · dm⁻³ aqueous hydrochloric acid (HCl) and of MgCl₂ · 6H₂O(s) in aqueous (approximately 1 mol · dm⁻³ HCl + MgCl₂ + H₃BO₃) at T=298.15 K were determined. From a combination of these results with measured enthalpies of solution of boric acid (H₃BO₃) in HCl(aq) and of magnesium oxide (MgO) in aqueous (HCl + H₃BO₃) solution, together with the standard molar enthalpies of formation of MgO(s), H₃BO₃(s), MgCl₂ · 6H₂O(s) and H₂O(l), the standard molar enthalpy of formation of −(8812 ± 3) kJ · mol⁻¹ of 2MgO · 2B₂O₃ · MgCl₂ · 14H₂O was obtained. Thermodynamic properties of this compound were also calculated by group contribution method.     

Thermodynamic properties of methylvinylsulphide

Enthalpies of the overall decomposition reactions MX₂L₂(c) → MX₂(c) + 2L(g) and of the intermediate stepwise loss of ligand, L, where X is Cl or Br; L is 3-chloropyridine, 3-bromopyridine, 2-chloropyridine, 2-bromopyridine, or 2-methoxypyridine; and M is Mn, Ni, Cu, or Cd have been measured by use of a differential scanning calorimeter. Enthalpies of sublimation of NiCl₂(3-chloropyridine)₂, NiCl₂(3-bromopyridine)₂ and CuCl₂(3-bromopyridine)₂ have been determined. Values of the metal—nitrogen bond dissociation energies in these compounds have been calculated. A value for the specific heat of CuCl₂(2-chloropyridine)₂ is reported.     

Vibrational spectra of cyclopropenes. II. IR spectra of 1,2-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for the 1,2-dimethyl-3-phenylcyclopropene (I) and 1,2-diphenylcyclopropene (II) molecules. The forms of the normal vibrations were determined, and the vibrations associated with vibrations of the exo- and endocyclic bonds of the ring were distinguished. It was shown that substitution at the double bond of cyclopropene leads to a change in the form of the symmetrical vibration of the ring in comparison with the vibration of unsubstituted cyclopropene. It was shown that a significant hypsochromic shift of the band of the symmetrical ring vibration in 1,2-disubstituted cyclopropenes in comparison with cyclopropenes that do not contain substituents at the C^1,2 atoms is due chiefly to the kinematic effect of the substituent. It was found that the introduction of substituents at the double bond of the ring leads to a decrease in the force constant of the double bonds.St. Petersberg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 125–132, January–February, 1993.     

Vibrational spectra of cyclopropenes. I. IR spectra of 3,3-disubstituted cyclopropenes

The IR spectra were measured and the vibrational problem was solved for a series of 3,3-disubstituted cyclopropenes [R¹: CH₃; R²: C(CH₃)₃ (I), C₆H₅ (II), CC–C(CH₃)₃ (III), CCH (IV)]. It was shown that a number of vibrations of the cyclopropene ring [symmetrical vibration of the ring, stretching and deformational (planar and out-of-plane) vibrations of the vinyl C–H bonds] are characteristic in frequency and form. On the basis of an analysis of the influence of a substituent at the C³ atom on the force field and the frequencies of the characteristic vibrations, it was concluded that the effect of conjugation of the substituent with _Walsh of the MO of the ring on the distribution of electron density in the ring plays a determining role.St. Petersberg University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 112–124, January–February, 1993.     

Palladium-catalyzed hydrophosphorylation and hydrophosphinylation of cyclopropenes

Novel transition-metal-catalyzed addition of P-H entities across the cyclopropene double bond has been developed. This transformation allows for mild and efficient preparation of phosphorus-containing cyclopropanes in good yields and high degrees of diastereoselectivity.     

Direct palladium-catalyzed arylation of cyclopropenes

The first examples of direct palladium-catalyzed arylation and heteroarylation of cyclopropenes have been demonstrated. This method allows for efficient synthesis of various tetrasubstituted cyclopropenes, incuding nonracemic cyclopropenes, which are not available via known asymmetric cyclopropenation methods. Mechanistic studies strongly suggest an electrophilic path for this Heck-type transformation.     

Enantioselective palladium-catalyzed carbozincation of cyclopropenes

A highly enantioselective palladium-catalyzed carbozincation of cyclopropenes has been developed. The intermediate cyclopropylzinc species, after transmetalation with copper, were trapped with various electrophiles. This one-pot procedure furnished functionalizied cyclopropenes with excellent diastereo- and enantioselectivity.     

Solid phase synthesis of cyclopropenes

Cyclopropene derivatives of high purity were prepared by reaction of acetylenes with a rhodium carbenoid bound to a polystyrene resin. This solid phase method avoids the formation of undesired byproducts obtained in the corresponding solution reaction and an eventual extension to combinatorial synthesis of cyclopropene derivatives could be achieved.     

Catalytic enantioselective hydroboration of cyclopropenes

2,2-Disubstituted cyclopropyl boronates have been synthesized with high degrees of diastereo- and enantioselectivity via the rhodium-catalyzed asymmetric hydroboration of 3,3-disubstituted cyclopropenes. A strong directing effect of ester and alkoxymethyl substituents has been demonstrated. The directing effect was found to be necessary in achieving high degrees of enantiomeric induction. Selected cyclopropylboronic derivatives were successfully employed in the Suzuki cross-coupling reaction to produce the corresponding optically active aryl- and vinylcyclopropanes in good yields.     

Thermodynamic properties of cerium mononitride

Data on the thermodynamic properties of cerium mononitride CeN in the solid state are analyzed. Relations approximating the temperature dependence of the thermodynamic functions of CeN(cr.) in the temperature range of 298.15–2900 K are obtained. Using the relations of thermodynamics known for this temperature range, the thermodynamic functions of cerium mononitride (entropy, Gibbs energy, and enthalpy variation) are calculated. The resulting data is entered into the database of the IVTANTHERMO software package and is used to analyze the thermal stability of CeN(cr.), and to estimate its boiling point at atmospheric pressure.