Showing papers by "José Elguero published in 2015"
01 Jan 2015
TL;DR: In this paper, extensive ab initio MP2/aug’-cc-pVTZ studies have been carried out in our laboratories to determine the structures, binding energies, bonding properties, and EOM-CCSD spin-spin coupling constants of various series of complexes stabilized by pnicogen bonds.
Abstract: Extensive ab initio MP2/aug’-cc-pVTZ studies have been carried out in our laboratories to determine the structures, binding energies, bonding properties, and EOM-CCSD spin-spin coupling constants of various series of complexes stabilized by pnicogen bonds. These systematic studies provide insight into the nature of the pnicogen bond, and how changes in this bond are reflected in the properties of these complexes.
74 citations
TL;DR: The charge-assisted complexes between PH3X(+) and PH2X have been analyzed and it was found that three different configurations could be formed, i.e. those linked through a P···P or a P·X pnicogen bond and those linkedthrough a P-H·P hydrogen bond, which are the most stable ones corresponding to the strongest interactions.
Abstract: The charge-assisted complexes between PH3X+ and PH2X have been analyzed. MP2/aug′-cc-pVTZ calculations were performed and the results were supported by the Quantum Theory of Atoms in Molecules approach and the Natural Bond Orbitals method. It was found that three different configurations could be formed, i.e. those linked through a P⋯P or a P⋯X pnicogen bond and those linked through a P–H⋯P hydrogen bond. The P⋯P configurations are the most stable ones corresponding to the strongest interactions; for all complexes the P⋯P configuration exists, while the P⋯X and P–H⋯P ones are present only for some of them. Different relations between the parameters were found, especially for the P⋯P interactions where there are correlations between the P⋯P distance and the electron density at the P⋯P bond critical point (ρPP) as well as between ρPP and the charge transfer energy.
70 citations
TL;DR: Dramatic synergistic cooperative effects have been found between the Be···F beryllium bonds and the Cl···N halogen bonds in ternary complexes, and EOM-CCSD spin-spin coupling constants (1X)J(Cl-N) across the halogen bond in these complexes also provide evidence of the same evolution of the Halogen-bond type.
Abstract: Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the structures, binding energies, and bonding characteristics of binary complexes HFBe:FCl, R2Be:FCl, and FCl:N-base, and of ternary complexes HFBe:FCl:N-base and R2Be:FCl:N-base for R = H, F, Cl; N-base = NH3, NHCH2, NCH. Dramatic synergistic cooperative effects have been found between the Be⋯F beryllium bonds and the Cl⋯N halogen bonds in ternary complexes. The Cl⋯N traditional halogen bonds and the Be⋯F beryllium bonds in binary complexes become significantly stronger in ternary complexes, while the F–Cl bond weakens. Charge-transfer from F to the empty p(σ) orbital of Be leads to a bending of the XYBe molecule and a change in the hybridization of Be, which in the limit becomes sp2. As a function of the intrinsic basicity of the nitrogen base and the intrinsic acidity of the Be derivative, the halogen-bond type evolves from traditional to chlorine-shared to ion-pair bonds. The mechanism by which an ion-pair complex is formed is similar to that involved in the dissociative proton attachment process. EOM-CCSD spin–spin coupling constants 1XJ(Cl–N) across the halogen bond in these complexes also provide evidence of the same evolution of the halogen-bond type.
47 citations
TL;DR: In this paper, a theoretical study of the XNO2 homodimers (X = F, Cl, Br and I) has been carried out by means of the Moller-Plesset methodology.
Abstract: A theoretical study of the XNO2 homodimers (X = F, Cl, Br and I) has been carried out by means of the Moller–Plesset (MP2) methodology. Twenty-two different minimum structures have been found, involving pnictogen, chalcogen and halogen bonds. MP2 interaction energies range between −0.4 to −17.5 kJ mol−1. Atoms in molecules (AIM) and natural bond orbital (NBO) approaches have been used to analyse the nature of the interaction within both monomers, obtaining good correlations between Laplacian values and bond distances. NBO E(2) orbital interaction energies are found to be up to 39.0 kJ mol−1. Charge transfer between monomers is in agreement with those in AIM and NBO findings, showing the highest charge transferred in those asymmetric dimers which involve pure halogen bonds. Symmetry adapted perturbation theory (SAPT-DFT) results show that the interactions are driven by the dispersion term, followed by the electrostatic one. The induction term presents the lowest contribution with the exception of complexes 1 and 5 of the iodine derivative in which E(2)i shows the maximum contribution to the total forces.
46 citations
TL;DR: Several bis(triazolium)-based receptors have been synthesized as chemosensors for anion recognition and theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum-energy conformation for all the complexes that explains their measured properties.
Abstract: Several bis(triazolium)-based receptors have been synthesized as chemosensors for anion recognition. The central naphthalene core features two aryltriazolium side-arms. NMR experiments revealed differences between the binding modes of the two triazolium rings: one triazolium ring acts as a hydrogen-bond donor, the other as an anion-π receptor. Receptors 9(2+)⋅2BF4(-) (C6H5), 11(2+)⋅2BF4(-) (4-NO2-C6H4), and 13(2+)⋅2BF(4-) (ferrocenyl) bind HP2O7(3-) anions in a mixed-binding mode that features a combination of hydrogen-bonding and anion-π interactions and results in strong binding. On the other hand, receptor 10(2+)⋅2 BF4(-) (4-CH3O-C6H4) only displays combined Csp2-H/anion-π interactions between the two arms of the receptors and the bound anion rather than triazolium (CH)(+)⋅⋅⋅anion hydrogen bonding. All receptors undergo a downfield shift of the triazolium protons, as well as the inner naphthalene protons, in the presence of H2PO4(-) anions. That suggests that only hydrogen-bonding interactions exist between the binding site and the bound anion, and involve a combination of cationic (triazolium) and neutral (naphthalene) C-H donor interactions. Theoretical calculations relate the electronic structure of the substituent on the aromatic group with the interaction energies and provide a minimum-energy conformation for all the complexes that explains their measured properties.
44 citations
TL;DR: Ab initio MP2/aug'-cc-pVTZ calculations were performed to investigate the pnicogen-bonded complexes F(4-n)H(n)P(+):N-base, finding that the particular acid-base pair is a factor in determining the binding energies of these complexes.
Abstract: Ab initio MP2/aug'-cc-pVTZ calculations were performed to investigate the pnicogen-bonded complexes F(4-n)H(n)P(+):N-base, for n = 0-3, each with a linear or nearly linear F-P···N alignment. The nitrogen bases include the sp(3) bases NH3, NClH2, NFH2, NCl2H, NCl3, NFCl2, NF2H, NF2Cl, and NF3 and the sp bases NCNH2, NCCH3, NP, NCOH, NCCl, NCH, NCF, NCCN, and N2. The binding energies vary between -20 and -180 kJ·mol(-1), while the P-N distances vary from 1.89 to 3.01 A. In each series of complexes, binding energies decrease exponentially as the P-N distance increases, provided that complexes with sp(3) and sp hybridized bases are treated separately. Different patterns are observed for the change in the binding energies of complexes with a particular base as the number of F atoms in the acid changes. Thus, the particular acid-base pair is a factor in determining the binding energies of these complexes. Three different charge-transfer interactions stabilize these complexes. These arise from the nitrogen lone pair to the σ*P-F(ax), σ*P-F(eq), and σ*P-H(eq) orbitals. The dominant single charge-transfer energy in all complexes is N(lp) → σ*P-F(ax). However, since there are three N(lp) → σ*P-F(eq) charge-transfer interactions in complexes with F4P(+) and two in complexes with F3HP(+), the sum of the N(lp) → σ*P-F(eq) charge-transfer energies is greater than the N(lp) → σ*P-F(ax) charge-transfer energies in the former complexes, and similar to the N(lp) → σ*P-F(ax) energies in the latter. The total charge-transfer energies of all complexes decrease exponentially as the P-N distance increases. Coupling constants (1p)J(P-N) across the pnicogen bond vary with the P-N distance, but different patterns are observed for complexes with F4P(+) and complexes of the sp(3) bases with F3HP(+). These initially increase as the P-N distance decreases, reach a maximum, and then decrease with decreasing P-N distance as the P···N bond acquires increased covalent character. For the remaining complexes, (1p)J(P-N) increases with decreasing P-N distance. Complexation increases the P-F(ax) distance and (1)J(P-F(ax)) relative to the corresponding isolated ion. (1)J(P-F(ax)) correlates quadratically with the P-N distance.
42 citations
TL;DR: Patterns exist which suggest that changes in (1)J(P-H(ax)) reflect the hybridization of the nitrogen base and whether the complex is an inner or outer complex, whereas outer complexes are stabilized by intermolecular P···N bonds with little or no covalency.
Abstract: Ab initio MP2/aug’-cc-pVTZ calculations have been carried out on cationic pnicogen-bonded complexes F4P+:N-base and F3HP+:N-base, with linear Fax–P···N and Hax-P···N, respectively. The bases include the sp3-hybridized nitrogen bases NH3, NClH2, NFH2, NCl2H, NCl3, NFCl2, NF2H, NF2Cl, and NF3, and the sp bases NCNH2, NCCH3, NP, NCOH, NCCl, NCH, NCF, NCCN, and N2. The binding energies of these complexes span a wide range, from −15 to −180 kJ mol–1, as do the P–N distances, which vary from 1.89 to 3.11 A. There is a gap in the P–N distances between 2.25 and 2.53 A in which no complexes are found. Thus, the equilibrium complexes may be classified as inner or outer complexes based on the value of the P–N distance. Inner complexes have P···N bonds with varying degrees of covalent character, whereas outer complexes are stabilized by intermolecular P···N bonds with little or no covalency. Charge-transfer stabilizes these pnicogen-bonded complexes. For complexes F4P+:N-base, the dominant charge-transfer interaction...
38 citations
TL;DR: It has been shown that the significant electron density rearrangements that follow the formation of a beryllium bond may lead to the appearance of a σ-hole in systems that previously do not exhibit this feature, such as CH3 OF, NO2 F, NO3 F, and other fluorine-containing systems.
Abstract: This work was partially supported by the Ministerio de Economia y Competitividad (Projects No. CTQ2012-35513-C02 and CTQ2013-43698-P), by the STSM COST Action CM1204, and by
the Project FOTOCARBON-CM S2013/MIT-2841 of the Comunidad Autonoma de Madrid. OB acknowledges a FPU grant from the Ministerio de Educacion, Cultura y Deporte of Spain. Computational time at Centro de Computacion Cientifica (CCC) of Universidad Autonoma de Madrid is also acknowledged.
37 citations
TL;DR: Pnicogen-bond radii for P in PH2X molecules have been determined from the P-P distances in the homodimers, and the sum of these radii provides an excellent approximation to theP-P distance in the corresponding binary complex.
Abstract: Ab initio MP2/aug′-cc-pVTZ calculations have been carried out on the pnicogen-bonded homodimers (PH2X)2 and the binary complexes H2XP:PYH2, for X, Y = F, Cl, OH, NC, CCH, CH3, CN, and H. The binding energies of these complexes are influenced by the nature of the X,Y pair, the intermolecular distance, the relative orientation of the interacting molecules, and the charge-transfer energies from the lone pair of one P to the σ-hole of the other. Binary complexes with X,Y = F, Cl, OH, and NC, as well as the homodimers, have a trans arrangement of the P–A and P–A′ bonds with respect to the P···P bond, with A and A′, the atoms of X and Y, respectively, bonded to the P atoms. The trendlines for the homodimers in plots of the binding energy versus the P–P distance, and the binding energy versus the total charge-transfer energy, exhibit better correlations than the trendlines for the binary complexes. The trendlines for the homodimers mark the boundary of the region in which points for the binary complexes appear. ...
37 citations
TL;DR: Theoretical calculations of 87 atranes, 113 considering the different endo/exo conformations, with combinations of B, C, N, Al, Si, P and Ge atoms at the bridgehead positions have been performed at the B3LYP/6-311++G(d,p) level as mentioned in this paper.
30 citations
TL;DR: The structure of a new equimolar 1:1 cocrystal formed by 3,5-dimethyl-1H-pyrazole (dmpz) and 4,5 -imidazole (dmim) is presented, determined by means of powder X-ray diffraction data combined with solid-state NMR that provided insight into topological details of hydrogen bonding connectivities and weak interactions such as CH···π contacts.
TL;DR: In this paper, MP2/aug′-cc-pVTZ calculations have been carried out to explore the PX3:NCH and PX 3:NH3 potential surfaces, with X = F, Cl and Br.
TL;DR: Calculated structures, binding energies, and bonding properties of complexes involving the cation and a set of sp-hybridized nitrogen bases show that charge-transfer energies stabilize all complexes and also exhibit an exponential dependence on the corresponding intermolecular distances.
Abstract: Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures, binding energies, and bonding properties of complexes involving the cation (H2C═PH2)(+) and a set of sp-hybridized nitrogen bases including NCCH3, NP, NCCl, NCH, NCF, NCCN, and N2. On each (H2C═PH2)(+):N-base surface, four types of unique equilibrium structures exist: a complex with a P···N pnicogen bond formed through the π system of (H2C═PH2)(+) (ZB-π); a complex with a P···N pnicogen bond formed through the σ system of (H2C═PH2)(+) (ZB-σ); a hydrogen-bonded complex with a P-H···N hydrogen bond (HB); and a tetrel-bonded complex with a C···N bond (TB). Binding energies of complexes stabilized by the same type of intermolecular interaction decrease in the order NCCH3 > NP > NCCl > NCH > NCF > NCCN > N2. For a given base, binding energies decrease in the order ZB-π > HB > ZB-σ > TB, except for a reversal of HB and ZB-σ with the weakest base N2. Binding energies of ZB-π, HB, and ZB-σ complexes increase exponentially as the corresponding P-N distance decreases, but the correlation is not as good between the binding energies of TB complexes and the intermolecular C-N distance. Charge-transfer energies stabilize all complexes and also exhibit an exponential dependence on the corresponding intermolecular distances. EOM-CCSD spin-spin coupling constants (1p)J(P-N) for ZB-π and ZB-σ complexes, and (2h)J(P-N) for HB complexes increase quadratically as the corresponding P-N distance decreases. Values of (1t)J(C-N) for TB are small and show little dependence on the C-N distance. (1)J(P-H) values for the hydrogen-bonded P-H bond in HB complexes correlate with the corresponding P-H distance, whereas values of (1)J(P-H) for the non-hydrogen-bonded P-H correlate with the P-N distance.
TL;DR: In this paper, the basicity of a set of 150 pyrazoles covering a range of about 200 kJ mol−1 in proton affinity and 10-15 pKa units was investigated.
Abstract: This study deals with the basicity, both in the gas phase and in an aqueous solution, of a set of 150 pyrazoles covering a range of about 200 kJ mol−1 in proton affinity and 10–15 pKa units. There are 63 NH-pyrazoles, in many cases, with two different tautomers and 87 N-substituted pyrazoles. The gas phase results are well reproduced by DFT theoretical calculations when the less stable tautomers are removed. For the pKa values to be reproduced adequately by calculations, some of the tautomers need to be removed, and the use of dummy variables accounting for the protonation on exocyclic amine groups is required and the conformation of the 5-phenyl groups need to be considered. Using these restrictions a large number of unknown pKas can be predicted and a few errors corrected.
TL;DR: In this paper, the authors characterizedyanophosphine derivative dimers, [HXP(CN)] 2 with X = H, F, Cl, and Cl, by means of CCSD(T)/aug′-cc-pVTZ/MP2/aug′ -cc-PVTZ computational level calculations and showed that compounds with dipole-dipole interactions present shorter contact distances and larger binding energies than those with pure P···P pnicogen bonds.
TL;DR: In this article, a mechanism for the formation of hydrazine is proposed, and the position of the aryl substituents on the bicyclic ring has been established by the combined use of NMR and DFT calculations.
TL;DR: The chemical shifts and several 19F–19F, 13C– 19F and 1H–19f spin‐spin coupling constants (SSCSs) of eight 4,5,6,7‐tetraflurobenzazoles (three benzimidazoles, three benzimidsolinones and two indazoles) have been determined.
Abstract: The chemical shifts and several 19F–19F, 13C–19F and 1H–19F spin-spin coupling constants (SSCSs) of eight 4,5,6,7-tetraflurobenzazoles (three benzimidazoles, three benzimidazolinones and two indazoles) have been determined. The chemical shifts were discussed using gauge including atomic orbital-density functional theory calculations taking into account solvent effects (polarizable continuum model) and, for the solid state, hydrogen bonds (clusters up to three molecules). Copyright © 2015 John Wiley & Sons, Ltd.
TL;DR: The tautomerism of 3- and 5-hydroxypyrazole is studied at the B3LYP, CCSD and G3B3 computational levels, including the gas phase, PCM-water effects, and proton transfer assisted by water molecules, which shows a significant reduction of the transition barriers upon solvation.
Abstract: We gratefully acknowledge support from the Ministerio de Economia y Competitividad (Project No. CTQ2012-35513-C02-02) and the Comunidad Autonoma de Madrid (S2013/MIT-2841, Fotocarbon). G.S.-S. thanks the Human Frontier Science Program (Project Reference: LT001022/2013-C) for their support. Thanks are given to the Irish Centre for High-End Computing (ICHEC) and the Trinity Center for High-Performance Computing (TCHPC) for the provision of computational facilities. Aoife Crowe and Dr. Cathy Kelly are acknowledged for their careful reading and help
TL;DR: In this paper, the properties of complexes formed between H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H, and the possible bridging molecules HNNH, FNNH and HNCHOH were investigated.
Abstract: Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the properties of complexes formed between H2XP, for X = F, Cl, NC, OH, CN, CCH, CH3, and H, and the possible bridging molecules HNNH, FNNH, and HNCHOH. H2XP:HNNH and H2XP:FNNH complexes are stabilized by P⋯N pnicogen bonds, except for H2(CH3)P:FNNH and H3P:FNNH which are stabilized by N–H⋯P hydrogen bonds. H2XP:HNCHOH complexes are stabilized by P⋯N pnicogen bonds and nonlinear O–H⋯P hydrogen bonds. For a fixed H2XP molecule, binding energies decrease in the order HNCHOH > HNNH > FNNH, except for the binding energies of H2(CH3)P and H3P with HNNH and FNNH. Binding energies of complexes with HNCHOH and HNNH increase as the P–N1 distance decreases, but binding energies of complexes with FNNH show little dependence on this distance. The large binding energies of H2XP:HNCHOH complexes arise from a cooperative effect involving electron-pair acceptance by P to form a pnicogen bond, and electron-pair donation by P to form a hydrogen bond. The dominant charge-transfer interaction in these complexes involves electron-pair donation by N across the pnicogen bond, except for complexes in which X is one of the more electropositive substituents, CCH, CH3, and H. For these, lone-pair donation by P across the hydrogen bond dominates. AIM and NBO data for these complexes are consistent with their bonding characteristics, showing molecular graphs with bond critical points and charge-transfer interactions associated with hydrogen and pnicogen bonds. EOM-CCSD spin–spin coupling constants 1pJ(P–N) across the pnicogen bond for each series of complexes correlate with the P–N distance. In contrast, 2hJ(O–P) values for complexes H2XP:HNCHOH do not correlate with the O–P distance, a consequence of the nonlinearity of these hydrogen bonds.
TL;DR: In this article, six new 3(5)-trifluoromethyl-5(3)-substituted-styryl-1 H -pyrazoles have been synthesized and their tautomerism studied in solution and in the solid state.
TL;DR: A theoretical study of the beryllium bonds in BeR2:C6X6 (R = H, F, Cl and X = H and F) has been carried out by means of MP2/aug′-cc-pVDZ computational methods, providing a clear indication of favorable cooperativity in both interactions observed, bryllium bond and aromatic ring:anion interaction.
Abstract: A theoretical study of the beryllium bonds in BeR2:C6X6 (R = H, F, Cl and X = H and F) has been carried out by means of MP2/aug′-cc-pVDZ computational methods. In addition, the ternary complexes BeR2:C6X6:Y− (Y = Cl and Br) have been analyzed. Geometric, energetic and electronic aspects of the complexes have been taken into account. All the parameters analyzed provide a clear indication of favorable cooperativity in both interactions observed, beryllium bond and aromatic ring:anion interaction.
TL;DR: There are frequent situations both in supramolecular chemistry and in crystallography that result in stereogenic centers, whose absolute configuration needs to be specified, so the inclusion of one simple additional rule stating that noncovalent interactions have a fictitious number between 0 and 1 is proposed.
TL;DR: In this article, the authors thanks to Prof. T. Breczewski for helping in DSC measurements, which has been funded by the Ministerio de Ciencia e Innovación (CTQ2010-67616122) and Ministerio De Economia y Competitividad of Spain (CTE2012-35513-C02-02) and Comunidad Autonoma de Madrid (Project MADRISOLAR2, ref. S2009/PPQ-1533).
Abstract: Authors thanks to Prof. T. Breczewski
for helping in DSC measurements. This work has been
financed by Ministerio de Ciencia e Innovacion (CTQ2010-
16122) and Ministerio de Economia y Competitividad of
Spain (CTQ2012-35513-C02-02) and Comunidad Autonoma
de Madrid (Project MADRISOLAR2, ref. S2009/PPQ-1533).
This work was also supported by the Basque Government
(project IT779-13)
TL;DR: In this paper, a theoretical study of metaphosphoric acid hydration to yield phosphoric acid has been carried out by means of MP2/6-31+G(d,p) and MP 2/aug-cc-pVTZ computational levels.
Abstract: A theoretical study of the hydration of metaphosphoric acid to yield phosphoric acid has been carried out by means of MP2/6-31+G(d,p) and MP2/aug-cc-pVTZ computational levels. Up to three explicit water molecules have been considered as well as the PCM solvation model to account for the effect of the bulk water. The reaction profile has been analyzed using the conceptual DFT methodology. The reactant structure is very dependent on the number of water molecules. The inclusion of more than one water molecule produces important cooperative effects and a shortening of the O···P pnictogen interaction besides the reaction barrier drops about 50 kJ mol−1. Reaction force at ξ
1 indicates the decreasing in the angular stress in the reaction site before reaching the TS as more explicit water molecules are taken into account. The analysis of the reaction electronic flux shows that for the three mechanisms studied, the principal reactive changes occur in the TS zone, while reactants and products remain in a zero-flux regime.
TL;DR: In this article, the influence of halogen bonds on the tautomerism of 9-methyl guanine and GTP was analyzed using Free-Wilson model to obtain the individual interactions.
TL;DR: Evaluation of basal and ligand-induced activity proved that several compounds showed agonist activity at the PPARα receptor, thus validating the oxazolidinone template for PPAR activity.
Abstract: A series of new peroxisome proliferator activated receptors (PPARs) chiral ligands have been designed following the accepted three-module structure comprising a polar head, linker, and hydrophobic tail. The majority of the ligands incorporate the oxazolidinone moiety as a novel polar head, and the nature of the hydrophobic tail has also been varied. Docking studies using the crystal structure of an agonist bound to the ligand binding domain of the PPARα receptor have been performed as a tool for their design. Suitable synthetic procedures have been developed, and compounds with different stereochemistries have been prepared. Evaluation of basal and ligand-induced activity proved that several compounds showed agonist activity at the PPARα receptor, thus validating the oxazolidinone template for PPAR activity. In addition, two compounds, 2 and 4, showed dual PPARα/PPARγ agonism and interesting food intake reduction in rats.
TL;DR: The possibility of forming stable BeR2 :ArH:Y(-) ternary complexes in which the beryllium compounds and anions are located on the opposite sides of an extended aromatic system is explored by means of MP2/aug-cc-pVDZ ab initio calculations.
Abstract: The possibility of forming stable BeR2 :ArH:Y(-) (R=H, F, Cl; ArH=naphthalene, pyrene; Y=Cl, Br) ternary complexes in which the beryllium compounds and anions are located on the opposite sides of an extended aromatic system is explored by means of MP2/aug-cc-pVDZ ab initio calculations. Comparison of the electron-density distribution of these ternary complexes with the corresponding BeR2 :ArH and ArH:Y(-) binary complexes reveals the existence of significant cooperativity between the two noncovalent interactions in the triads. The energetic effects of this cooperativity are quantified by evaluation of the three-body interaction energy Δ(3) E in the framework of the many-body interaction-energy (MBIE) approach. Although an essential component of the interaction energies is electrostatic and is well reflected in the changes in the molecular electrostatic potential of the aromatic system on complexation, strong polarization effects, in particular for the BeR2 :ArH interactions, also play a significant role. The charge transfers associated with these polarization effects are responsible for significant distortion of both the BeR2 and the aromatic moieties. The former are systematically bent in all the complexes, and the latter are curved to a degree that depends on the nature of the R substituents of the BeR2 subunit.
TL;DR: In this paper, the effect of halogen bonds (XBs) on the position of the equilibrium has been investigated on three tautomeric pairs of 3-mercapto-1,2-azoles (pyrazoles, isoxazoles, and isothiazoles).
Abstract: DFT calculations at the B3LYP/6-311++G(d,p) computational level have been carried out on three tautomeric pairs of 3-mercapto-1,2-azoles (pyrazoles, isoxazoles, and isothiazoles) to study the effect of halogen bonds (XBs) on the position of the equilibrium. As halogen bond donors, we have selected Br2, Cl2, BrCl, ClF and BrF and compare them with HF as a hydrogen bond donor. Several linear relationships were found between binding energies of different halogen bond donors. The main conclusion of this study is that the XB inverts the tautomeric equilibrium while an HB does not.
TL;DR: Raman spectroscopy was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, and to try to clarify the scarce data existing about both the formation of deprotonated enediol and the aldo-enedioate equilibrium.
Abstract: The biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2-enediol or 1,2-enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, actually a 1,2-enediolate, and to try to clarify the scarce data existing about both the formation of deprotonated enediol and the aldo-enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, that is, hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z-enediolate forms takes place at basic pH, together with an increase in the concentration of aldehyde species, such as 2-oxoethan-1-olate, and a decrease in the concentrations of the hydrated aldehyde and dimeric forms. The theoretical ratio of ≈1.5:1 for aldehyde:Z-enediolate reproduces the experimental Raman spectrum in basic medium, with an additional contribution of the previously mentioned ratio between the hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and conclude that aldo-enediol tautomerism-formally aldo-enediolate-happens when a suitable amount of basic species is added.
TL;DR: In this paper, the authors used a contract from the Ministerio de Economia y Competitividad (M.M.-L) and the Comunidad Autonoma deMadrid (CARBON) with financial support from the CTI and CSIC.