ROH Molecules Research Articles

The Solvation of Ca2+ with Gas Phase Clusters of Alcohol Molecules

A comprehensive examination of how the identity of an alcohol molecule can change the behavior of a solvated, alkaline earth dication has been undertaken. The metal dication of Ca2+ has been clustered with a range of different alcohols to form [Ca(ROH)n]2+ complexes, where n lies in the range 2–20. Following collisional activation via electron capture from nitrogen gas, complexes for n in the range 2–6 exhibit a switch in reaction product as a function of n. For low values, solvated CaOH+ is the dominant fragment, but as n increases beyond 4, this is displaced by the appearance of solvated CaOR+. A separate study of unimolecular metastable decay by [Ca(ROH)n]2+ complexes found evidence of charge separation to form CaOH+(ROH)n−1 + R+. For two isomers of butanol, the n = 3 complexes were found to follow parallel, but different metastable pathways: one leading to the appearance of CaOH+ and another that resulted in proton abstraction to form ROH2+. These differences have been attributed to the precursor complexes adopting geometries where one ROH molecule occupies a secondary solvation shell. Comparisons were made with a previous study of magnesium complexes; [Mg(ROH)n]2+ show that the difference in second ionization energy Mg+ (15.09 eV) as opposed to Ca+ (11.88 eV) influences behavior. A complex between Ca2+ and 1-chloroethanol is shown to favor the formation of CaCl+ as opposed to CaOH+ as a unimolecular charge separation product, which is attributed to differences in bond energy in the precursor molecule.

Polysubstituted 3-trifluoromethylpyrazoles: regioselective (3 + 2)-cycloaddition of trifluoroacetonitrile imines with enol ethers and functional group transformations.

Non-catalysed addition of trifluoroacetonitrile imines to enol ethers provided fully regioselectively (3 + 2)-cycloadducts, which either spontaneously or via Brønsted acid-induced elimination of ROH molecules led to the formation of 3-trifluoromethylated pyrazoles. In the case of 2,3-dihydrofuran, the respective bicyclic intermediate was isolated and its structure was confirmed by X-ray analysis. Using the developed protocol the synthesis of a known antitumor compound SC-560 was performed in 45% yield. Subsequent functionalisations of selected 4-(ω-hydroxyalkyl)pyrazoles at C(5) through lithiation/addition, cross-coupling reactions or via intramolecular Pd-catalysed C-H arylations opened up an access to polysubstituted pyrazoles including unusual tricyclic systems comprising 7-membered rings (oxepane, thiepane and azepane) as the central unit.

A case of Z/E-isomers elution order inversion caused by cosolvent percentage change in supercritical fluid chromatography

A case of elution order inversion caused by cosolvent percentage change in supercritical fluid chromatography was observed and investigated in some detail. Z- and E-isomers of phenylisobutylketone oxime experience an elution order reversal on most columns if the mobile phase consists of CO2 and alcohol. At lower percentages of alcohol Z-oxime is retained less, somewhere at 2–5% coelution occurs and at larger cosolvent volume elution order reverses – Z-oxime is eluted later than E-oxime. We suppose inversion with CO2-ROH phases happens due to a shift in balance between two main interactions governing retention. At low ROH percentages stationary phase surface is only slightly covered by ROH molecules so oximes primarily interact with adsorption sites via hydrogen bond formation. Due to intramolecular sterical hindrance Z-oxime is less able to form hydrogen bonds and consequently is eluted first. At higher percentages alcohols occupy most of strong hydrogen bonding sites on silica surface thus leaving non-specific electrostatic interactions predominantly responsible for Z/E selectivity. Z-oxime has a much larger dipole moment than E-oxime and at these conditions it is eluted later. Additional experimental data with CO2-CH3CN, hexane-iPrOH and CHF3-ROH mobile phases supporting this explanation are presented.

A family of cationic oxime-based hexametallic manganese(iii) single-molecule magnets

Three novel cationic hexametallic Mn(III) compounds of formulae [Mn6(μ3-O)2(H2N-sao)6(py)6(EtOH)2](ClO4)2·4EtOH (1), [Mn6(μ3-O)2(H2N-sao)6(tpy)6(H2O)2](ClO4)2·2tpy·4H2O·2EtOH (2) and [Mn6(μ3-O)2(H2N-sao)6(Him)6(EtOH)2](ClO4)2·6EtOH (3) [H2N-saoH2 = salicylamidoxime, py = pyridine, tpy = 4-tert-butylpyridine and Him = imidazole] have been synthesised and magnetostructurally characterised. These [Mn6](2+) complexes are new members of the oxime-based family of neutral [Mn6] single-molecule magnets (SMMs) in which the previously terminally bonded carboxylates, phosphinates, halides or ROH molecules on the outwardly facing triangular faces have been replaced with pyridine (1), 4-tert-butylpyridine (2) and imidazole (3) molecules generating a new series of salts based on Mn6 complexes. These results suggest that the cationic [Mn6](2+) species could be used as suitable building blocks for preparing new materials with different functionalities.

Concerted Reactions and Mechanism of Glucose Pyrolysis and Implications for Cellulose Kinetics

Concerted reactions are proposed to be keys to understanding thermal decomposition of glucose in the absence of ionic chemistry, including molecular catalysis by ROH molecules such as H(2)O, other glucose molecules, and most of the intermediates and products. Concerted transition states, elementary-reaction pathways, and rate coefficients are computed for pyrolysis of β-D-glucose (β-D-glucopyranose), the monomer of cellulose, and for related molecules, giving an improved and elementary-reaction interpretation of the reaction network proposed by Sanders et al. (J. Anal. Appl. Pyrolysis, 2003, 66, 29-50). Reactions for ring-opening and formation, ring contraction, retro-aldol condensation, keto-enol tautomerization, and dehydration are included. The dehydration reactions are focused on bicyclic ring formations that lead to levoglucosan and 1,6-β-D-anhydrousglucofuranose. The bimolecular ROH-assisted reactions are found to have lower activation energy compared to the unimolecular reactions. The same dehydration reaction to levoglucosan should occur for cellulose going to cellosan (e.g., cellotriosan) plus a shortened cellulose chain, a hypothesis supported by the very similar activation energies computed when alternate groups were substituted at the C1 glycosidic oxygen. The principles of Sanders et al. that distinguish D-glucose, D-fructose, sucrose, and cellulose pyrolysis prove useful in providing qualitative insights into cellulose pyrolysis.

Simultaneous Measurements of Droplet Size and Transient Temperature Within Surface Water Droplets

A lifetime-based molecular tagging thermometry technique was developed for achieving simultaneous measurements of droplet size and transient temperature distribution within a small water droplet over a solid surface. For molecular tagging thermometry measurements, a pulsed laser is used to tag phosphorescent 1-BrNp · Mβ-CD ·ROH molecules premixed within a small water droplet Long-lived laser-induced phosphorescence is imaged at two successive times after the same laser excitation pulse. While the size of the water droplet (in terms of volume, height, contact area, and contact angle of the water droplet) can be determined instantaneously from the acquired phosphorescence images, the transient temperature measurement is achieved by taking advantage of the temperature dependence of phosphorescence lifetime, which is estimated from the intensity ratio of the acquired phosphorescence image pair. The feasibility and implementation of the lifetime-based molecular tagging thermometry technique were demonstrated by conducting simultaneous measurements of droplet size and spatially and temporally resolved temperature distribution inside a convectively-cooled microsized water droplet over an aluminum test plate to quantify the unsteady mass and heat transfer processes within the small water droplet to elucidate underlying physics to improve our understanding about microphysical phenomena associated with aircraft icing studies.

Proton-Transfer and H2-Elimination Reactions of Trimethylamine Alane: Role of Dihydrogen Bonding and Lewis Acid−Base Interactions

Proton-transfer and H(2)-elimination reactions of aluminum hydride AlH(3)(NMe(3)) (TMAA) with XH acids were studied by means of IR and NMR spectroscopy and DFT calculations. The dihydrogen-bonded (DHB) intermediates in the interaction of the TMAA with XH acids (CH(3)OH, (i)PrOH, CF(3)CH(2)OH, adamantyl acetylene, indole, 2,3,4,5,6-pentafluoroaniline, and 2,3,5,6-tetrachloroaniline) were examined experimentally at low temperatures, and the spectroscopic characteristics, dihydrogen bond strength and structures, and the electronic and energetic characteristics of these complexes were determined by combining experimental and theoretical approaches. The possibility of two different types of DHB complexes with polydentate proton donors (typical monodentate and bidentate coordination with the formation of a symmetrical chelate structure) was shown by DFT calculations and was experimentally proven in solution. The DHB complexes are intermediates of proton-transfer and H(2)-elimination reactions. The extent of this reaction is very dependent on the acid strength and temperature. With temperature increases the elimination of H(2) was observed for OH and NH acids, yielding the reaction products with Al-O and Al-N bonds. The reaction mechanism was computationally studied. Besides the DHB pathway for proton transfer, another pathway starting from a Lewis complex was discovered. Preference for one of the pathways is related to the acid strength and the nucleophilicity of the proton donor. As a consequence of the dual Lewis acid-base nature of neutral aluminum hydride, participation of a second ROH molecule acting as a bifunctional catalyst forming a six-member cycle connecting aluminum and hydride sites notably reduces the reaction barrier. This mechanism could operate for proton transfer from weak OH acids to TMAA in the presence of an excess of proton donor.

The Solvation of Mg2+ with Gas-Phase Clusters Composed of Alcohol Molecules

The dication Mg2+ has been clustered with a range of different alcohols to form [Mg(ROH)N]2+ complexes, where N lies in the range 2-10. Observations on the chemistry of the complexes reveal two separate patterns of behavior: (i) unimolecular metastable decay, where at small values of N the complexes undergo rapid charge separation via Coulomb explosion; and (ii) electron capture-induced decay, where collisional activation promotes bond-breaking processes via charge reduction. For the latter it has been possible to identify a generic set of reactions that are common to all of the different [Mg(ROH)N]2+ complexes; however, there are examples of reactions that are specific to individual alcohols and values of N. For metastable decay, it is shown that there is a clear correlation between the value of N at which a complex ceases to be metastable and the ionization energy of R, the radical that forms the complementary ion in the Coulomb explosion step. Metastable decay in two of the [Mg(ROH)N]2+ complexes follows a very different pathway that eventually results in proton abstraction. It is suggested that this difference is due to the precursor complexes adopting geometries that have at least one ROH molecule in a secondary solvation shell.

Molecular tagging thermometry for transient temperature mapping within a water droplet

We present the progress made in developing a molecular tagging thermometry (MTT) technique for achieving spatially and temporally resolved temperature measurements within a small water droplet over a solid surface. For MTT measurement, a pulsed laser is used to tag phosphorescent 1-BrNp.Mbeta-CD.ROH molecules premixed with water. Long-lived laser-induced phosphorescence is imaged at two successive times after the same laser excitation pulse. The temperature measurement is achieved by taking advantage of the temperature dependence of the phosphorescence lifetime, which is estimated from the intensity ratio of the acquired phosphorescence image pair. The measured transient temperature distributions can be used to quantify the unsteady heat transfer process inside convectively cooled water droplets over smooth or rough surfaces.

Singlet Excited‐State Interactions in Naphthalene–Thymine Dyads

Two thymidine-derived nucleosides 1 and 2 were prepared by attaching a chiral naphthalene to the positions 5' and 3' of the sugar. The resulting dyads, which contain key substructures present in drugs and nucleic acids, exhibit different spatial arrangements (transoid or cisoid) of the fluorophore relative to the thymine unit. Emission measurements on these compounds in the presence of ROH molecules revealed a remarkable intramolecular prescence quenching for dyad 1. The obtained results are consistent with quenching of the singlet excited state of 1 by hydrogen-bond donor solvents. Thus, a physical deactivation process (vibronically induced internal conversion) would be the pathway responsible for the accelerated decay of 1*, favorably competing with fluorescence and intersystem crossing to the triplet. This effect appears to be strongly dependent on the relative spatial arrangement between the naphthalene and thymine units, together with the hydrogen-bonding ability of the employed ROH.

Control of the ratio of functional and non-functional ligands in clusters of the type Zr6O4(OH)4(carboxylate)12for their use as building blocks for inorganic–organic hybrid polymers

The methacrylate ligands of the cluster Zr6O4(OH)4(methacrylate)12 undergo degenerate exchange with methacrylic acid in solution. Addition of propionic or isobutyric acid allows partial or complete exchange of the methacrylate ligands for propionate or isobutyrate. The mixed-carboxylate cluster Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) was independently prepared by reaction of Zr(OnBu)4 with a mixture of methacrylic acid and isobutyric acid. The structures of Zr6O4(OH)4(OMc)8(isobutyrate)4(BuOH) and Zr6O4(OH)4(isobutyrate)12(H2O) consist of an octahedral Zr6(μ3-O)4(μ3-OH)4 core with one of the carboxylate ligands being monodentate. The H2O or ROH molecule is coordinated to the neighbouring zirconium atom and, at the same time, hydrogen bonded to the monodentate carboxylate. A mechanism for the carboxylate exchange is suggested based on the structural observations.

Influence of media and homoconjugate pairing on transition metal hydride protonation. An IR and DFT study on proton transfer to CpRuH(CO)(PCy3).

The interaction of the ruthenium hydride complex CpRuH(CO)(PCy(3)) (1) with proton donors HOR of different strength was studied in hexane and compared with data in dichloromethane. The formation of dihydrogen-bonded complexes (2) and ion pairs stabilized by hydrogen bonds between the dihydrogen ligand and the anion (3) was observed. Kinetics of the interconversion from 2 to 3 was followed at different (CF(3))(3)COH concentrations between 200 and 240 K. The activation enthalpy and entropy values for proton transfer from the dihydrogen-bonded complex 2 to the (eta(2)-H(2))-complex 3 (DeltaH() = 11.0 +/- 0.5 kcal/mol and DeltaS() = -19 +/- 3 eu) were obtained for the first time. The results of the DFT study of the proton transfer process, taking CF(3)COOH and (CF(3))(3)COH as a proton donors and introducing solvent effects in the calculation with the PCM method, are presented. The role of homoconjugate pairs [ROHOR](-) in the protonation is analyzed by means of the inclusion of an additional ROH molecule in the calculations. The formation of the free cationic complex [CpRu(CO)(PCy(3))(eta(2)-H(2))](+) is driven by the formation of the homoconjugated anionic complex [ROHOR](-). Solvent polarity plays a significant role stabilizing the charged species formed in the process. The theoretical study also accounts for the dihydrogen release and production of CpRu(OR)(CO)(PCy(3)), observed at temperatures above 250 K.

Kinetics of the reaction of ozone with tert-butanol

The kinetics of tert-butanol (ROH) oxidation by ozone in CCl4 and H2O solutions at 295 K is studied by spectrophotometry under batch conditions. The rate-limiting step of the process in both solvents is the reaction of ozone with the monomeric form of ROH. In H2O, the hydrated molecules of ROH and ozone react with each other. In CCl4, the association of ROH molecules, which changes the kinetics and mechanism of the process, should be taken into account. The reaction kinetic parameters and the dimerization constant of ROH in CCl4 are determined.

Gas-phase polar [4++2] cycloaddition of cationic 2-azabutadienes with enol ethers

Polar [4++2] cycloaddition of the prototype cationic 2-azabutadiene with ethyl vinyl ether was recently reported, and its potential application for the structural analysis of enol ethers suggested [R. Augusti, F.C. Gozzo, L.A.B. Moraes, R. Sparrapan, M.N. Eberlin, J. Org. Chem. 63 (1998) 4889]. We now report that the gaseous N-methyl 2-azabutadienyl cation (MAB+) reacts similarly, readily and generally with alkyl, silyl, and thio-enol ethers. The intact cycloadducts are formed abundantly, and collision-induced dissociation of acyclic enol ether cycloadducts occurs competitively by RDA and by the characteristic loss of either a ROH, (CH3)3SiOH, or RSH neutral molecule. Cycloadducts of acyclic enol ethers that bear no double bond substituents also form upon RO(S)H loss a characteristic fragment of m/z 96. For the cycloadducts of enol ethers bearing double-bound substituents (R1), the RO(S)H loss fragment displays a mass shift that corresponds to the mass of R1. Endocyclic enol ethers also react readily by MAB+ cycloaddition, but unless affected by ring substituents, the dissociation of their cycloadducts is dominated by RDA. Detailed structural information of the reactant enol ethers is therefore provided, and positional isomers are easily distinguished. Gas-phase polar [4++2] cycloaddition with cationic 2-azabutadienes, as demonstrated here for MAB+, is therefore class-selective and structurally diagnostic for enol ethers and their analogs.

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing.

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.

The formation of [RuCl( p-cymene)(Me 2HPz)(PPh 2OR)]Cl (Me 2HPz=3, 5-dimethylpyrazole; R=H, Me and p-Tol) complexes from the cleavage of the P–N bond of a P-coordinated P(Me 2Pz)Ph 2 ligand by ROH molecules in a ruthenium(II) complex. Crystal structure of [RuCl( p-cymene)(Me 2HPz)(PPh 2OH)]Cl

The complex [RuCl 2( p-cymene)] 2 reacts with 1-(3,5-dimethyl)pyrazolyldiphenylphosphine (P(Me 2Pz)Ph 2) to give the complex RuCl 2( p-cymene)(P(Me 2Pz)Ph 2). This compound reacts with ROH molecules (R=H, Me and p-Tol) to give [RuCl( p-cymene)(Me 2HPz)(PPh 2OR)]Cl (R=H, Me and p-Tol) complexes, which contain both Me 2HPz and PPh 2OR coordinated molecules.

Migration of a Proton as a Function of Solvation within {ROH}n{H2O}H+ Cluster Ions: Experiment and Theory

Metastable and collision-induced decompositions of mass-selected {ROH}n{H2O}H+ cluster ions (where R ≡ CH3−, CH3CH2−, CH3CH2CH2−, and (CH3)2CH−) were observed to exhibit distinct size-dependent behavior. We observe that loss of a water molecule is dominant for n ≤ 8, whereas loss of multiple ROH molecules is the favored decomposition channel for n ≥ 9, resulting in the eventual formation of a stable {ROH}9{H2O}H+ cluster ion. We believe this is evidence for two distinct cluster geometries which explicitly depend on the number of ROH molecules present. That is, below a certain critical size the proton resides on the molecule with the highest proton affinity, the ROH. However, above that critical cluster size the proton will now preferentially reside on the water molecule, if there are sufficient alcohols to completely and symmetrically solvate the central H3O+. The structural implications of these results will be discussed in light of new theoretical calculations which have been performed on this system.

The adsorption and dissociation of ROH molecules on TiO 2(110)

First-principles calculations based on density-functional theory and the pseudopotential method are used to investigate the energetics of adsorption of the series of molecules H 2O, CH 3OH, H 2O 2 and HCO 2H on the TiO 2(110) surface. The aim of the work is to elucidate the factors that determine whether the adsorption is molecular or dissociative, including the acidity of the molecule, the geometry and electrostatic properties of the surface, and the interaction between adsorbed species. It is shown that the theoretical methods reproduce experimental values of the gas-phase heterolytic and homolytic dissociation energies to reasonable accuracy (within ∼20 kJ mol −1 for all four molecules). We find that the adsorption energy for the most favourable molecular mode of adsorption is extremely close to that for dissociative adsorption in the cases of H 2O, CH 3OH and H 2O 2. For HCO 2H, dissociative adsorption is favoured by a substantial margin, provided the dissociated geometry preserves the equivalence of the two oxygens in the formate ion. It is also shown that the geometry of the TiO 2(110) surface plays a crucial role in determining the conformations of the most stable geometries, and that hydrogen bonding between adsorbed species is also important.

Kinetics and mechanism of intramolecular general base‐catalyzed alkanolysis of phenyl salicylate in the presence of anionic micelles

AbstractThe alkanolysis of ionized phenyl salicylate, PS−, has been studied in the presence and absence of micelles of sodium dodecyl sulphate, SDS, at 0.05 M NaOH, 30 or 32°C and within the alkanol, ROH, (ROH = HOCH2CH2OH and CH3OH) contents of 15–74 or 92%, v/v. The alkanolysis of PS− involves intramolecular general base catalysis. At a constant concentration of SDS, [SDS]T, the observed pseudo first‐order rate constants, kobs, for the reactions of ROH with PS− obtained at different concentration of ROH, [ROH]T, obey the relationship: kobs = k[ROH]T/(1 + KA[ROH]T) where k is the apparent second‐order rate constant and KA is the association constant for dimerization of ROH molecules. Both k and KA decrease with increase in [SDS]T. At a constant [ROH]T, the rate constants, kobs, show a decrease of nearly 2‐fold with increase in [SDS]T from 0.0–0.3M. These results are explained in terms of pseudo‐phase model of micelle. The rate constants for alkanolysis of PS− in micellar pseudophase are insignificant compared with the corresponding rate constants in aqueous‐alkanol pseudophase. This is attributed largely to considerably low value of [ROH] in the specific micellar environment where micellar bound PS− molecules exist. The increase in [ROH]T decrease the value of the binding constant of PS− with SDS micelle. The effects of anionic micelles on the rates of alkanolysis of PS− are explained in terms of the porous cluster micellar structure.

Interpretation of infrared intensities based on the atomic polar tensor partition. The ROH molecules (R = H, CH 3, NH 2, OH, F)

The Atomic Polar Tensors (APT) of the H atom for ROH molecules where R = H, CH 3, NH 2, HO and F, are calculated by the ab initio method using the 4–31 G basis set. The results are interpreted in terms of the charge, charge-flux, atomic dipole flux and homopolar dipole flux contributions.