Blue-shifting Hydrogen Bonds Research Articles

HNO(H2O) n (n = 1–4) clusters: a theoretical study

The geometrical structure, binding energy, and vibrational spectra of small clusters of nitrosyl hydride (HNO) and water molecules, HNO(H2O)n, where (n = 1–4), have been investigated at the MP2 level of theory, using 6-311++G(2d,2p) basis set. We located three dimers, six trimers, nine tetramers, and three pentamers at the MP2/6-311++G(2d,2p) computational level. Particular attention is given to existence and magnitude of NH···O blue-shifting hydrogen bonds. Blue shifts of the NH stretching frequency upon complex formation in the ranges between 28 and 151 cm−1 is predicted. Cooperative effect in terms of stabilization energy along with the many-body interaction energies analysis was performed for the studied clusters. The Atoms in Molecules (AIM) theory was also applied to explain the nature of the complexes.

Hydrogen bond and halogen bond inside the carbon nanotube

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.

Existence of both blue-shifting hydrogen bond and Lewis acid–base interaction in the complexes of carbonyls and thiocarbonyls with carbon dioxide

In this study, 16 gas phase complexes of the pairs of XCHZ and CO(2) (X = F, Cl, Br; Z = O, S) have been identified. Interaction energies calculated at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ level including both BSSE and ZPE corrections range from -5.6 to -10.5 kJ mol(-1) for XCHOCO(2) and from -5.7 to -9.1 kJ mol(-1) for XCHS···CO(2). Substitution of one H atom by one halogen in formaldehyde and thioformaldehyde reduces the interaction energy of XCHZ···CO(2), while a CH(3) substitution increases the interaction energy of both CH(3)CHO···CO(2) and CH(3)CHS···CO(2). NBO and AIM analyses also point out that the strength of Lewis acid-base interactions decreases going from >C1=S3···C6 to >C1=O3C6 and to >C1-X4···C6. This result suggests the higher capacity of solubility of thiocarbonyl compounds in scCO(2), providing an enormous potential application for designing CO(2)-philic materials based on the >C=S functional group in competition with >C=O. The Lewis acid-base interaction of the types >C=S···C, >C-Cl···C and >C-Br···C is demonstrated for the first time. The contribution of the hydrogen bonding interaction to the total interaction energy is larger for XCHS···CO(2) than for XCHO···CO(2). Upon complexation, a contraction of the C1-H2 bond length and a blue shift of its stretching frequency have been observed, as compared to the isolated monomer, indicating the existence of a blue-shifting hydrogen bond in all complexes examined. Calculated results also lend further support for the viewpoint that when acting as proton donor, a C-H bond having a weaker polarization will induce a stronger distance contraction and frequency blue shift upon complexation, and vice versa.

First-principles study of fluoroform adsorption on a hexagonal ice (0001) surface: weak hydrogen bonds—strong structural effects

For isolated fluoroform (F(3)CH) molecules adsorbed on a hexagonal ice (0001) surface the properties of blue- and red-shifting hydrogen bonds were studied using static density functional theory (DFT) calculations and Car-Parrinello molecular dynamics (CP-MD) simulations. A systematic search by starting from many initial configurations was performed to determine the lowest-energy structures of F(3)CH on the ice surface, and for the optimized geometries the vibrational frequencies were calculated. The local minima structures are analyzed in terms of their coordination to the surface, with special focus on identifying blue-shifting hydrogen bonds via their spectroscopic signature of an increased frequency of the C-H fundamental stretching vibration. Subsequently, by CP-MD simulations the stability of the lowest-energy configurations at finite temperatures was verified and possible transformation pathways connecting the local minima structures were explored.

Theoretical Study of Formic Acid−Sulfur Dioxide Dimers

We report the first theoretical study of noncovalent and covalent interactions in formic acid (FA)-SO(2) complexes. Using ab initio and DFT model chemistries, five stable noncovalent complexes were identified, as well as a covalent adduct, formic sulfurous anhydride HOSO(2)CHO. syn-FA is predicted to form two nonplanar bidentate complexes with SO(2): the more stable one contains a normal hydrogen bond donated by OH, and the less stable one contains a blue-shifted hydrogen bond donated by CH. Both are stabilized by charge transfer from FA to SO(2). anti-FA forms three planar complexes of nearly equal energy containing OH-to-SO(2) hydrogen bonds. Formic sulfurous anhydride forms via an endothermic concerted cycloaddition. Natural bond orbital analysis showed that the bidentate SO(2)-FA complexes are stabilized by n → π* donation from FA to SO(2), and back-donation from SO(2) n and π* orbitals into FA σ(OH)* or σ(CH)* orbitals. The bidentate formic acid-SO(2) complex that contains an O-H···O hydrogen bond is more stable than the similar nitric acid-SO(2) complex. The latter contains a stronger hydrogen bond but shows no O→S charge transfer interaction.

Molecular structure and vibrational spectra of 2,6-bis(benzylidene)cyclohexanone: A density functional theoretical study

The near-infrared Fourier transform (NIR-FT) Raman and Fourier transform infrared (FT-IR) spectral analyses of 2,6-bis(benzylidene)cyclohexanone (BBC) molecule, a potential drugs for the treatment of P388 leukemia cells, were carried out along with density functional computations. The optimized geometry of BBC using density functional theory shows that the energetically favored chair conformation is not observed for central cyclohexanone ring and is found to possess a nearly ‘half chair’ conformation and shows less expansion of the angles and more rotation about the bonds. The existence of intramolecular C–H⋯O improper, blue-shifted hydrogen bond was investigated by means of the NBO analysis. The lowering of carbonyl stretching vibration can be attributed to the mesomeric effect and the π-orbital conjugation induced by the unsaturation in the α-carbon atoms and co-planarity of the (–CH C–(C O)–C CH–) group.

An ab initio and QTAIM study of hydrogen bonded clusters of nitrosyl hydride with ammonia

Ab initio calculations at MP2/6-311++G(d,p) computational level were used to analyze the interaction between a molecule of the nitrosyl hydride with 1 up to 4 molecules of ammonia. Three minima were found for 1:2 and 1:4 complexes of HNO and NH 3. Four complexes were located as minima on the potential energy surface of 1:3 complexes. Particular attention is given to existence and magnitude of NH⋯N blue-shifting hydrogen bonds. Blue shifts of the N–H stretching frequency upon complex formation in the ranges between 33 and 105 cm −1 are predicted. Cooperative effect in terms of stabilization energy is calculated for the studied clusters. The cooperative effect is increased with the increasing size of studied clusters. The Quantum Theory Atoms in Molecules (QTAIM) theory was also applied to explain the nature of the complexes.

Theoretical analysis of the (HNO)2, (HNO···HNS), and (HNS)2 dimers — A case of red and blue shifts of N–H stretching frequency

The hydrogen-bonded interactions in the simple (HNZ)2 dimers, with Z = O and S, were investigated using quantum chemical calculations with the second-order Møller–Plesset perturbation (MP2), coupled-cluster with single, double (CCSD), and triple excitations (CCSD(T)) methods in conjunction with the 6-311++G(2d,2p), aug-cc-pVDZ, and aug-cc-pVTZ basis sets. Six-membered cyclic structures were found to be stable complexes for the dimers (HNO)2, (HNS)2, and (HNO–HNS). The pair (HNS)2 has the largest complexation energy (–11 kJ/mol), and (HNO)2 the smallest one (–9 kJ/mol). A bond length contraction and a frequency blue shift of the N–H bond simultaneously occur upon hydrogen bond formation of the N–H···S type, which has rarely been observed before. The stronger the intramolecular hyperconjugation and the lower the polarization of the X–H bond involved as proton donor in the hydrogen bond, the more predominant is the formation of a blue-shifting hydrogen bond.

On the Difference of the Properties between the Blue-Shifting Halogen Bond and the Blue-Shifting Hydrogen Bond

The difference of the properties between the blue-shifting halogen bond and the blue-shifitng hydrogen bond has been investigated at the M06/6-311++G(d,p) theory level. It was found that the three lone electron pairs on the halogen atom play an important role for the difference of the properties between the blue-shifting halogen bond and the blue-shifitng hydrogen bond. The additional electron-density transfer from the three lone electron pairs on the halogen atom to the remote part of the halogen atom donor (i.e., the antibonding orbitals of the bonds other than X-Hal) makes the blue-shifting halogen bond much more ubiquitous in the halogen-bonded complexes than the blue-shifitng hydrogen bond in the hydrogen-bonded complexes, and it also makes the values of the X-Hal bond contraction generally much larger than the values of the X-H bond contraction. The difference of the properties between the X-Cl...Y blue-shifting halogen bond and the X-Br...Y blue-shifting halogen bond was also discussed.

The hydrogen bonding network in the dimer of syn-N-phenyl-N′-sulfinylhydrazine, PhNHNSO

N-phenyl-N′-sulfinylhydrazine (PhNHNSO) has been analyzed with infrared spectroscopic and computational methods. Experimental infrared spectra show a red shift of the frequency of the N H stretching vibration from monomer to dimer, confirming the presence of intermolecular N H⋯O hydrogen bonding interactions suggested from diffraction studies in the solid state. Computational investigations of the monomer confirm the preference of the syn configuration, as found in the dimer, over sickle and anti isomers. An analysis of the electron density within the framework of the quantum theory of Atoms in Molecules reveals the presence of intermolecular N H⋯O and C H⋯O interactions in the dimer, thus suggesting an alternate hydrogen bonding network from the one proposed from diffraction studies. The N H⋯O and C H⋯O interactions are identified as hydrogen bond and blue-shifting hydrogen bond, respectively.

Blue shifted hydrogen bond in 3-methylindole·CHX3 complexes (X = Cl, F)

Although the first experimental report on the blue shifted hydrogen bond in gas phase appeared about a decade ago, not many examples have been reported in the literature thereafter. Computational studies on systems exhibiting such blue shifted hydrogen bond however have been abundant since then. Many of these theoretical predictions remain to be verified experimentally. In this work we present an example of blue shifted hydrogen bond observed in the weakly bound complexes of 3-methylindole and CHX(3) (X = F, Cl). The complexes were prepared using the supersonic jet expansion method and studied using the laser spectroscopic methods. The key findings were that these complexes exhibit C-Hpi type hydrogen bonding interaction and the CH is bound to the phenyl part of the aromatic plane. The CH stretch was found to be blue shifted by 2 and 16 cm(-1) in the case of CHCl(3) and CHF(3), respectively. Ab initio calculations along with atoms-in-molecule analysis and natural bond orbital analysis support the experimental findings. The computed results at the DFT/MP2 level also indicated that the IR intensity of the H-bond donor CH-stretch increases by two to three orders of magnitude for the CHCl(3) complex whereas for the fluoroform complex the same decreases by an order of magnitude, which are consistent with the trend reported in the case of C-HO type of blue shifting hydrogen bonds.

On the physical origin of the cation–anion intermediate bond in ionic liquids Part I. Placing a (weak) hydrogen bond between two charges

The intermediate bond forces in ionic liquids are investigated from static quantum chemical calculations at various methods and two basis sets. The experimentally observed red-shift of the donor-proton bond stretching frequency due to a bond elongation is confirmed by all methods. Comparing Hartree-Fock to second-order Møller-Plesset perturbation theory, the Hartree-Fock method gives in many cases an erroneous description of the geometries. Furthermore, the Hartree-Fock interaction energies can deviate up to 60 kJ mol(-1) from Møller-Plesset perturbation theory indicating the importance of dispersion interaction. While the usual trends of decreasing stability or interaction energies with increasing ion sizes are found, the geometries involving hydrogen atoms do not change this order of total interaction energies. Therefore, the hydrogen bond is not the most important interaction for ion pairs with regard to the total interaction energy. On the other hand, the different established analysis methods give rise to hydrogen bonding in several ion pairs. Charge analysis reveals the hydrogen-bonding character of the ion pair and shows, depending on the type of ions combined and further on the type of conformers considered, that a hydrogen bond can be present. The possibility of hydrogen bonding is also shown by an analysis of the frontier orbitals. Calculating potential energy surfaces and observing from this the change in the donor proton bond indicates that regular hydrogen bonds are possible in ion pairs of ionic liquids. Thereby, the maximum of bond elongation exceeds the one of a usual hydrogen bond by far. The more salt-like hydrogen-bonded ion pair [NH(4)][BF(4)] exhibits a steeper maximum than the more ionic liquid like ion pair [EtNH(3)][BF(4)]. The fact that imidazolium-based ionic liquids as [Emim][Cl] can display two faces, hydrogen bonding and purely ionic bonding, points to a disturbing rather than stabilizing role of hydrogen bonding on the interaction of the counterions in imidazolium-based ionic liquids. While geometry and charge analysis provides attributes of weak (blue-shifted) hydrogen bonds, large bond elongations accompanied by red-shifts are obtained for the ion pairs investigated. This can be understood by the simple fact that these imidazolium-based ionic liquid ion pairs constitute weak hydrogen bonds placed between two delocalized charges.

Hydrocarbons as proton donors in C–H⋯N and C–H⋯S hydrogen bonds

C–H⋯N and C–H⋯S hydrogen bonds were analyzed in complexes where acetylene, ethylene, methane and their derivatives are proton donors while ammonia and hydrogen sulfide are proton acceptors. Ab initio calculations were performed to analyze those interactions; MP2 method was applied and the following basis sets were used: 6-311++G(d,p), aug-cc-pVDZ and aug-cc-pVTZ. The results showed that hydrogen bonds for complexes with ammonia are systematically stronger than such interactions in complexes with hydrogen sulfide. If the fluorine substituted hydrocarbons are considered then F-substituents enhance the strength of hydrogen bonding. For a few complexes, mainly those where carbon atom in proton donating C–H bond possesses sp 3 hybridization, the blue-shifting hydrogen bonds were detected. Additionally, Quantum Theory of ‘Atoms in Molecules’ and Natural Bond Orbitals method were applied to analyze H-bond interactions.

A quantum chemical study of red-shift and blue-shift hydrogen bonds in bimolecular and trimolecular methylhydrazine-hydrate complexes

This study presents a theoretical discussion of the geometry and molecular parameters of the methylhydrazine-hydrate complex. Using B3LYP/6-311++G(d,p) calculations, two geometries for the methylhydrazine-hydrate complex were analyzed by considering the interaction between water in: (i) a lone nitrogen pair assisted by a methyl ( I); and (ii) the nitrogen of the NH 2 group ( II). These geometries were examined by examining the formation of (N···H) hydrogen bonds, which were characterized using ChelpG charge transfer amounts, as well as by means of topological parameters derived from Quantum Theory of Atoms in Molecules (QTAIM) calculations. In a qualitative evaluation, both complexes ( a) and ( b) were compared with the corresponding trimolecular system ( c) formed by methylhydrazine and two water molecules. A conclusion was then obtained by means of vibrational analysis, in which, in addition to δ υ(H–O) red-shifts in water molecules, the stretch frequency of the H–C bond of methyl group shifted upwards, indicating the formation of a blue-shifting hydrogen bond in the methylhydrazine-bihydrate complex.

A theoretical study of red-shifting and blue-shifting hydrogen bonds occurring between imidazolidine derivatives and PEG/PVP polymers

A theoretical study is presented with the aim to investigate the molecular properties of intermolecular complexes formed by the monomeric units of polyvinylpyrrolidone (PVP) or polyethyleneglycol (PEG) polymers and a set of four imidazolidine (hydantoine) derivatives. The substitution of the carbonyl groups for thiocarbonyl in the hydantoin scaffold was taken into account when analyzing the effect of the hydrogen bonds on imidazolidine derivatives. B3LYP/6-31G(d,p) calculations and topological integrations derived from the quantum theory of atoms in molecules (QTAIM) were applied with the purpose of examining the N-H···O hydrogen bond strengths formed between the amide group of the hydantoine ring and the oxygen atoms of PVP and PEG polymers. The effects caused by the N-H···O interaction fit the typical evidence for hydrogen bonds, which includes a variation in the stretch frequencies of the N-H bonds. These frequencies were identified as being vibrational red-shifts because their values decreased. Although the values of such calculated interaction energies are between 12 and 33 kJ mol(-1), secondary intermolecular interactions were also identified. One of these secondary interactions is formed through the interaction of the benzyl hydrogen atoms with the oxygen atoms of the PVP and PEG structures. As such, we have analyzed the stretch frequencies on the C-H bonds of the benzyl groups, and blue-shifts were identified on these bonds. In this sense, the intermolecular systems formed by hydantoine derivatives and PVP/PEG monomers were characterized as a mix of red-shifting and blue-shifting hydrogen-bonded complexes.

A theoretical study of blue-shifting hydrogen bonds in π weakly bound complexes

In this work, a theoretical study about vibrational blue-shifting hydrogen bonds in π weakly bound complexes formed by acetylene (C 2H 2···HCF 3), ethylene (C 2H 4···HCF 3), cyclopropene (C 3H 4···HCF 3), tetrahedrene (C 4H 2···HCF 3), and fluoroform (HCF 3) is presented. In these systems, the formation of the (π···H) interaction occurs through the charge transfer from hydrocarbons to fluoroform via contact between their π bonds and hydrogen atoms, respectively. By taking into account calculations performed at the B3LYP/6-311++G(d,p) level of theory, geometry results indicate a shortening of H–C bond of HCF 3, where in infrared vibrational analysis, this structural observation is known as a blue-shifting stretch mode. In other words, it was observed that the H–C stretch frequency is shifted to upward wavenumbers accompanied by a reduction on the absorption intensity. Energetically, these π complexes are weakly bound because their intermolecular energies are very low, varying from −1.3 kJ mol −1 to −4.7 kJ mol −1. Moreover, a theoretical explanation for blue-shifts on H–C bonds of the fluoroform was presented through the evaluation of the ChelpG atomic charges, by which the quantification of charge transfer was used in order to justify the strengthening on (π···H) hydrogen bond as follows: C 2H 2···HCF 3 > C 2H 4···HCF 3 > C 3H 4···HCF 3 > C 4H 2···HCF 3.

A PBE hybrid functional study of blue-shifting and red-shifting hydrogen bonds in pi hydrocarbons

This study examines a selected group of p hydrocarbon complexes, represented by C2H4•••HCF3, C2H2•••HCF3, C2H4•••HCF3 and C2H2•••HCF3, from a theoretical point of view. From BPBE/6-311++G(d,p) calculations, the geometrical results of these complexes revealed an elongation and shortening of the H—C bond lengths of chloroform (HCCl3) and fluoroform (HCF3), respectively. In terms of the infrared spectrum, the analysis of stretch frequencies revealed that the variations in the H—C modes are essentially recognized as red and blue-shifting modes. For the purposes of understanding the two vibrational phenomena of the ? hydrocarbon complexes studied here, PBE/6-311++G(d,p) calculations were carried out and partitioning of atomic charges derived from the ChelpG algorithm were also used. A theoretical justification of red- and blue-shift effects was drawn up using charge-transfer analysis, which is manifested in the ? bonds of acetylene and ethylene to chloroform (H—CCl3) and fluoroform (H—CF3), respectively. Finally, a further debate regarding the distinct polarizability power of chloroform and fluoroform is presented, concluding that, in comparison with fluoroform, chloroform possesses the requisite features for conventional proton donors and a red-shift is therefore observed in the C2H4•••HCCl3 and C2H2•••HCCl3 complexes.

Are the silyl group hydrogens in peri-substituted-9-silyltriptycenes engaged in blue-shifting hydrogen bonds?

In three 9-silyltriptycenes bearing chlorine, bromine and the methyl group in one of the peri positions, the silyl group suffers extreme hindrance of its reorientational motion. Owing to this, separate signals of the individual silyl group protons could be observed in NMR spectra at relatively high temperatures. For each compound, the measured values of J couplings of these protons to the 29Si nucleus are strongly diversified, especially when a halogen atom occurs in the peri position. These differences can be qualitatively interpreted in terms of electron density transfers from the peri substituent, causing the individual Si-H bonds to differentiate. The stereoelectronic picture revealed by natural bond orbital analysis fits the pattern normally interpreted as that of the blue-shifting hydrogen bond. However, an essential similarity of the stereoelectronic effects for both the halogen and methyl substituents raises a serious question about the applicability of that concept to the present case.

Spectroscopic analysis and DFT calculations of a food additive Carmoisine

FT-IR and Raman techniques were employed for the vibrational characterization of the food additive Carmoisine (E122). The equilibrium geometry, various bonding features, and harmonic vibrational wavenumbers have been investigated with the help of density functional theory (DFT) calculations. A good correlation was found between the computed and experimental wavenumbers. Azo stretching wavenumbers have been lowered due to conjugation and π-electron delocalization. Predicted electronic absorption spectra from TD-DFT calculation have been analysed comparing with the UV–vis spectrum. The first hyperpolarizability of the molecule is calculated. Intramolecular charge transfer (ICT) responsible for the optical nonlinearity of the dye molecule has been discussed theoretically and experimentally. Stability of the molecule arising from hyperconjugative interactions, charge delocalization and C–H⋯O, improper, blue shifted hydrogen bonds have been analysed using natural bond orbital (NBO) analysis.

Coexistence of S–H···O and N–H···O Blue-shifted Hydrogen Bonds in a Small System: HSO···HNO

Abstract Theoretical study indicates that the HSO···HNO complex possesses simultaneously two substantial blue-shifted H bonds: S–H···O and N–H···O. The blue shift of the S(N)–H stretching frequencies is due to an intricate combination of two shortening effects of the electron density decrease in the σ*[S(N)–H] and the rehybridization of spn S(N)–H hybrid orbitals.