Raman spectrocopic studies on the vibrational relaxation of CH3CN in different environments

Comparison of the frequencies and half-widths of v₁ in a variety of solvents shows that dispersion forces make a significant contribution to the effective intermolecular potential. Measurements of τ_v^?1 and [ω²] in the CH₃CN/CD₃OD/CCl₄ system demonstrates that long-range (hydrogen-bonding?) potentials significantly affect the relaxation rate.     

Reaction of [HO(CH2)3]3P with α,β-Unsaturated Ketones Containing a Phenylpropanoid Backbone

Abstract

Interaction of 3,4-(MeO)₂-benzylideneacetone with [HO(CH₂)₃]₃P (THPP) was studied in CD₃OD by NMR to compare reactivity of a phenylpropanoid α,β-unsaturated ketone with a corresponding α,β-unsaturated aldehyde. In the presence of HCl, both the ketone and a related cinnamaldehyde first establish an equilibrium with the product formed by nucleophilic attack of the THPP at the C?O bond, [ArCH?CHCX(OD)PR₃]⁺Cl^?(X?H or CH₃, Ar?Ph or 3,4-(MeO)₂C₆H₃). The ketone salt then slowly transforms into [R₃PCH(Ar)CH(D)C(O)CD₃]⁺Cl^?, the phosphonium product of nucleophilic attack of THPP at the C?C bond, whereas the final product from the aldehyde is the (α-ether)phosphonium chloride [ArCH?CHCH(OCD₃)PR₃]⁺Cl^?. In aqueous media, in the absence of HCl, 4-HO-benzylideneacetone, which is similar to a lignin-type, α,β-unsaturated aldehyde model compound, interacts with THPP to afford a stable phosphonium zwitterion, in contrast to the previously studied aldehyde model, which forms dimeric, bisphosphonium products.     

Isotope effects and H/D scrambling in the fragmentation of labelled propenes

The fragmentation reaction [C₃(H,D)₆]⁺· → [C₃(H,D)₅]⁺ + (H, D) has been examined in the metastable decomposition region for two pairs of labelled propenes: CH₃CD?CH₂,CD₃CH?CD₂ and CD₃CH?CH₂, CH₃CD?CD₂. The results indicate that complete hydrogen scrambling occurs in the propene molecular ion prior to fragmentation. The isotope effect kH/kD is in the range 2·1 to 3·3.     

Steric control in the base catalysed H-D exchange of an α,β-unsaturated ketone

For the base catalysed H-D exchange of the equatorial hydrogen and the axial hydrogen in 4-t-butyl-1-acetylcyclohex-1-ene (1) in CH₃OD containing CH₃ONa, k_eq/k_ax is 3.8:1. This is clearly a result of steric rather than stereoelectronic factors.     

η-Pentamethylcyclopentadienylruthenium(II) complexes containing η-coordinated α-amino acids

Reaction of [Cp* RuCl₂]₂ with -alanine ( -alaH) in methanol at room temperature in the presence of NaOMe yields the complex Na[Cp* RuCl( -ala)] (1), which contains a five-membered N,O-coordinated chelate ring. The analogous complex Na[Cp* RuCl( -phe)] (2) is obtained under similar conditions but at 0°C in 90% yield. At temperatures above 20°C both 2 and the η⁶-coordinated complex [Cp* Ru( -pheH)]Cl (4) are obtained, with the proportion of the latter increasing with temperature. Compound 4 is obtained in 88% yield by refluxing [Cp* RuCl₂]₂ and -phenylalanine ( -pheH) in CH₃OH/CH₃ONa followed by separation from 2. The analogous ruthenium(II) sandwich complexes 5–10 were obtained from -tyrosine and -tryptophane and various derivatives. [Cp* Ru( -met)] (3), prepared by the reaction of [Cp* RuCl₂]₂ with -methionine ( -metH) in CH₃OH/CH₃ONa, displays N,O,S-coordination.     

Reactions of [CH3]+ and [CD3]+ with alcohols

The reactions of [CH₃]⁺ and [CD₃]⁺ with a number of C₁ to C₅ alcohols were studied at approximately thermal energies (0.1 eV) using a tandem Dempster ion cyclotron resonance mass spectrometer. Branching ratios obtained under single collision conditions are reported for [CH₃]⁺ and [CD₃]⁺ with methanol, perdeutero methanol, ethanol, allyl alcohol, 1-propanol, 2-propanol, perdeutero-2-propanol, 1-butanol, 2-butanol, t-butanol, cyclopentanol and 1-pentanol. The results are examined in terms of the mechanism of reactions and indicate that upon progression to larger alcohols, the formation of a long-lived adduct becomes less important in determining the reaction products.     

Reaction of tris(hydroxymethyl)phosphine and cinnamaldehyde in methanol

Reaction of tris(hydroxymethyl)phosphine with excess cinnamaldehyde in CH₃OH or CD₃OD, followed using NMR, proceeds via several phosphorus-containing intermediates, multiple transformations of organic parts, and with the solvent H/D isotope effect on products. In both solvents, one CH₂OH group of tris(hydroxymethyl)phosphine is readily replaced by the cinnamaldehyde moiety to give the primary product, a 1,3-oxaphosphorinane derivative. Slower replacement of the second CH₂OH group leads to a mixture of aliphatic and heterocyclic phosphine intermediates in a ratio of ~4:1 in CH₃OH and ~1:1 in CD₃OD; both intermediates contain alcohol and aldehyde groups and convert rapidly into intra- and intermolecular hemiacetals. The hemiacetals of the aliphatic phosphine rearrange further into an unsymmetrical trialkylphosphine oxide, whereas the hemiacetals of the heterocyclic phosphine react with the third mole of cinnamaldehyde to replace the third CH₂OH group of tris(hydroxymethyl)phosphine. All intermediates and products are formed as mixtures of stereoisomers.     

The Chemical Ionization of Organic Compounds. 1st Communication. Linear alkenes with six to nine carbon atoms

The chemical ionization spectra of linear alkenes have been measured using H₂O, CH₄ or CD₃OD as ionizing gas. In the case of 1-heptene the dependence of spectra on pressure, temperature and repeller field strength has been measured and is discussed.     

Deuterium Isotope Effect on Excess Enthalpies of Methanol or Ethanol and Their Deuterium Derivatives at 298.15 K

Excess enthalpies of six binary mixtures of CH₃ OD+CH₃ OH, CH₃ OD+CD₃ OD, CD₃ OD+CH₃ OH, C₂ D₅ OD+C₂ H₅ OH, C₂ D₅ OD+C₂ H₅ OD, C₂ H₅ OD+C₂ H₅ OH have been determined over the whole range of mole fractions at 298.15 K in order to know the isotopic effect on hydrogen-bonding accurately, although there are many reports on the differences in the strength of hydrogen-bonding between OH and OD. All excess enthalpies measured are very small and endothermic. The mixtures of CH₃ OD+ CH₃ OH, and C₂ D₅ OD+C₂ H₅ OH showed the largest excess enthalpies among each methanol and ethanol mixtures. The difference of intermolecular interaction between OH and OD in methanol and ethanol was almost same value of (1.82±0.04) J mol^-1 Excess enthalpies of 1,4-dimethylbenzene+1,3-dimethylbenzene and 1,4-dimethylbenzene+1,2-methylbenzene were measured by three different principle calorimeters at 298.15 K in order to know the precision of calorimetry for a small enthalpy change. This revised version was published online in July 2006 with corrections to the Cover Date.     

1-Butyl-2,3-trimethyleneimidazolium bis(trifluoromethylsulfonyl)imide ([b-3C-im][NTf2]): a new, stable ionic liquid

Using imidazole as the starting material, the synthesis of a new bicyclic ionic liquid [b-3C-im][NTf₂] is described. Except for the alkylation reaction in the second step (40% yield) of this four-step synthesis of [b-3C-im][NTf₂], others were all high yielding reactions (85-94% isolated yields). We investigated intrinsic reactivity of this and other imidazolium-based ionic liquids and found that, under strongly basic conditions (KOD in CD₃OD/D₂O (1:1) solution), the new ionic liquid was stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] and [bdmim][PF₆] ionic liquids were 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. At the same experimental condition, the most commonly employed [bmim][PF₆] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases (CD₃OD/D₂O = 1:1), only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and other ionic liquids gave no detectable exchanges even after one week at ambient temperature. It is therefore concluded that the new [b-3C-im][NTf₂] ionic liquid is far more chemically stable than previously reported [bmim][PF₆], [bdmim][NTf₂], and [bdmim][PF₆].     

Electrochemical and ESR studies of the oxidation mechanism of pyrazine-di-N-oxides in the presence of methanol and its deuterated derivatives

The mechanism of oxidation of pyrazine-, 2,5-di-Me-, and 2,3,5,6-tetra-Me-pyrazine-di-N-oxides in the presence of methanol and its deuterated derivatives (CH₃OD, CD₃OD), i.e., compounds exhibiting the high energy of C-H bond dissociation, is studied by the methods of cyclic voltammetry, ESR electrolysis, and quantum chemical modeling. The study is carried out on a glassy carbon (GC) electrode in acetonitrile and on an Au electrode in solutions of different alcohols (methanol and its deuterated derivatives CH₃OD, CD₃OD). In alcohol solutions, the ESR spectra of radical cations and radical anions of the tested aromatic di-N-oxides are observed. The quantum chemical simulation of the reaction of the pyrazine-di-N-oxide radical cation with the MeOH C-H bond is carried out. The results obtained are explained within the framework of the E₁C₁E₂C₂ mechanism for a two-stage electrode process determined by the catalytic current of the second electrode stage. The overall two-electron catalytic oxidation of an alcohol within its complex with the pyrazine-di-N-oxide radical cation is proposed.     

Quasiclassical Trajectory Study of the Reaction of CD4 with O(1D)

Extensive quasiclassical trajectory calculations for the O(¹D)+CD₄ multichannel reaction were carried out on a new global potential energy surface fit by permutationally invariant polynomials. The product branching ratios, translational energy distributions, and angular distributions of OD+CD₃, D+CD₂OD/CD₃O, and D₂+DCOD/D₂CO product channels were calculated and compared with the available experimental results. Good agreement between theory and experiment has been achieved, indicating small isotope effects for the title reaction. The O(¹D)+CD₄ reaction mainly proceeds through the CD₃OD intermediate via the trapped abstraction mechanism, with initial abstraction of the D atom rather than the direct insertion, followed by decomposition of CD₃OD into various products.     

Investigation of the Nucleophilic Rearrangement of 2-(Cyanomethyl)-1,4,6-trimethylpyrimidinium Iodide Into 4,6-Dimethyl-2-methylaminonicotinic Acid Nitrile

2-(Cyanomethyl)-1,4,6-trimethylpyrimidinium iodide is rearranged into 4,6-dimethyl-2-methylaminonicotinic acid nitrile by interaction with alcoholic solutions of sodium ethylate, methylamine, and also glycine and -alanine ethyl esters. This conversion was also observed for the first time for pyrimidinium salts during the process of recording ¹H NMR spectra in CD₃OD solution containing CD₃ONa. After the rearrangement deuterium exchange of the protons of the pyridine ring methyl groups was noted spectrally. It was demonstrated experimentally that for carrying out and completing the recyclization a quantity of nucleophilic reagent must convert the molar equivalent quantity of pyridinium salt.     

The Photochemistry of the (Cycloalkene)(hydro)(trispyrazolylborato)iridium Complexes [Ir(η4-cod)(TpMe2)] and [Ir(η2-coe)H2(TpMe2)]: the Formation of [IrH4(TpMe2)] and [Ir(CO)H2(TpMe2)]

Photolysis of [Ir(η²-coe)H₂(Tp^Me2)] ( 1 ; Tp^Me2=hydrotris(3,5-dimethylpyrazolyl)borato, coe=(Z)-cyclooctene) in CH₃OH gives a mixture of [IrH₄(Tp^Me2)] ( 4 ) and [Ir(CO)H₂(Tp^Me2)] ( 5 ) in a ca. 1 : 1 ratio. Mass-spectral analysis of the distillate of the reaction mixture at the end of the photolysis shows the presence of coe. When pure CD₃OD is used as solvent, the deuteride complexes [IrD₄(Tp^Me2)] ((D₄)- 4 ) and [Ir(CO)D₂(Tp^Me2)] ((D₂)- 5 ) are obtained. Also the photolysis of [Ir(η⁴-cod)(Tp^Me2)] ( 3 ) (cod=cycloocta-1,5-diene) gives 4 and 5 . A key feature of this photoreaction is the intramolecular dehydrogenation of cod with formation of cycloocta-1,3,5-triene, detected by mass spectroscopy at the end of the photolysis. Labeling experiments using CD₃OD show that the hydrides in 4 originate from MeOH. When ¹³CH₃OH is used as solvent, [Ir(¹³CO)H₂(Tp^Me2)] is formed demonstrating that CH₃OH is the source of the CO ligand. The observation that the photolysis of both 1 and 3 give the same product mixture is attributed to the formation of a common intermediate, i.e., the coordinatively unsaturated 16e⁻ species {IrH₂(Tp^Me2)}.     

Conformational Analysis of the 1,3‐Oxaphosphorinanes Formed from α,β‐Unsaturated Aldehydes and the (Hydroxymethyl)phosphines RP(CH2OH)2 (R = Ph or CH2OH)

Equimolar reactions of cinnamaldehyde or its 3,5‐dimethoxy‐4‐hydroxy derivative (sinapaldehyde) with RP(CH₂OH)₂ (R = Ph or CH₂OH) were studied in MeOH or CD₃OD at room temperature by NMR spectroscopy. In MeOH, nucleophilic attack of the phosphine at the C?C bond, with concomitant loss of CH₂O, affords the tertiary phosphine HOCH₂P(R)CH(Ar)CH₂CHO ( 3 ) that rapidly converts mainly into a 1,3‐oxaphosphorinane derivative ( 5 ) formed as a mixture of four diastereomers. Conformational analysis reveals that the Ar group in these is exclusively in an equatorial position while the OH and R groups can be equatorial‐oriented or axial‐oriented. In CD₃OD, 1,3‐oxaphosphorinanes monodeuterated in the C5 position are obtained as a mixture of eight diastereomers where the dominate diastereomers have an axial D‐atom. Diastereomeric ratios depend on the nature of the Ar and R groups.     

Lignin-type, α,β-unsaturated aldehydes of lignin-type in organic solvents

A 1:1 reaction of [HO(CH₂)₃]₃P with 4-hydroxy-3-methoxy-cinnamaldehyde (coniferaldehyde) or 3,5-dimethoxy-4-hydroxycinnamaldehyde (sinapaldehyde) in acetone at room temperature affords phosphonium zwitterions of the type R₃P⁺CH(4-O^?-Ar)CH₂CHO; other phosphines [R = Et, n-Bu, (CH₂)₂CN, and p-Tol] do not react under the same conditions. In alcohols R??OH(D) [R?? = CD₃, Et, (CD₃)₂CD, s-Bu, HOCH₂CH₂], the above phosphines (except the cyano-derivative) and those where R = i-Pr, Cy, Me₂Ph, MePh₂ do react within an equilibrium established between the reactants and the zwitterion-hemiacetal products R₃P⁺CH(4-O^?-Ar)CH₂CH(OH)(OR??) that are formed as a mixture of two diastereomers. The nature of the phosphine and the alcohol affects the equilibrium and the diastereomeric ratio.     

Effect of strongly interacting solutes on group rotational correlation functions in ethanol

Proton magnetic relaxation rates of solutions of LiCl and LiI in isotopically labelled ethanols CH₃CD₃OD, CD₃CH₂OD and CD₃CD₂OH have been measured as functions of temperature and concentration mostly at v=30 MHz, where 21. The data were reduced in a way that revealed that CH₃ and CH₂ relaxation curves contained a residuum from the slow motion of the OH group in many cases. Thus, the rotational time correlation function of the CH₃ and CH₂ groups contain a residuum term stemming from the slow motion within the same molecule. The data show a threshold of the rotational energy which has to be exceeded in order to make the effect observable.     

Bond energies and thermal decomposition of [Pt(X)(CH3)(P(C2H5)3)2] complexes

The thermal decomposition of the complexes trans-[Pt(X)(CH₃)L₂] (L  P(C₂H₅)₃; X  Cl, Br, I, CN) in decalin at 170 and 200°C affords methane platinum metal and [Pt(X)₂L₂]. The kinetics of the decomposition of the complexes were determined by monitoring the appearance of methane by GLC. The observed first-order rate constant was found to be independent on the nature of the ligand X. The thermal decomposition of the trideuteriomethyl complexes [Pt(X)(CD₃)L₂] (X  I, CN) in decalin-d₁₈ at 170 and 200°C was studied by GLC/MS. The thermolysis affords CD₃H and CD₄ in ratios which are independent of the nature of X and of the temperature used. The mass spectra of the complexes were also examined. A relative scale of platinum-to-methyl bond dissociation energies has been established by measuring the appearance potential of the fragment ion [Pt(X)L₂]⁺ and the ionization energies in the series [Pt(X)(CH₃)L₂]. Ionization potentials and PtCH₃ bond energies show a clear dependence on the nature of X which is not reflected in corresponding changes in the decomposition rates.     

Selective Activation of the C−H Bond in Methane by Single Platinum Atomic Anions

Mass spectrometric analysis of the anionic products of interaction between platinum atomic anions, Pt^?, and methane, CH₄ and CD₄, in a collision cell shows the preferred generation of [PtCH₄]^? and [PtCD₄]^? complexes and a low tendency toward dehydrogenation. [PtCH₄]^? is shown to be H?Pt?CH₃^? by a synergy between anion photoelectron spectroscopy and quantum chemical calculations, implying the rupture of a single C?H bond. The calculated reaction pathway accounts for the observed selective activation of methane by Pt^?. This study presents the first example of methane activation by a single atomic anion.     

Angular dependence of 1H- and 2H-NMR spectra of water and methanol absorbed in cellulose triacetate film

¹H- and ²H-NMR spectra of water (H₂O and D₂O) and methanol (CH₃OD and CD₃OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. ¹H-NMR signals of H₂O and CH₃OD are doublets and triplets due to dipole interactions, respectively. ²H-NMR signals of D₂O, CD₃OH, and CH₃OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle-dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.