Monika Grundwald-Wyspiańska

Strong hydrogen bonds in 1:1 and 2:1 complexes of pyridine betaine with strong acids

Abstract The crystal structure of bis(pyridine betaine) hydrochloride- d 1 monohydrate- d 2 has been determined by X-ray analysis. The carboxylate groups of a pair of pyridine betaine molecules are bridged by a deuteron to form a centro-symmetric dimer featuring a very strong hydrogen bond of length 2.444(4) A. The geometric mass effect (Δ R ≈ 0.008 A) is well within the range observed for this type of hydrogen bond. The FT-IR spectra of polycrystalline 1:1 and 2:1 complexes of pyridine betaine with HNO 3 , HCl, HBr, HI, HO 3 SCF 3 , HClO 4 , HBF 4 , and H 2 SO 4 have been investigated in the 4000–200 cm −1 range. In the 1:1 complexes a proton is transferred from the acid to the betaine molecule, C 5 H 5 N + CH 2 COOH · A − , and both the νOH and νCO frequencies vary with the proton acceptor properties of the anion. The spectra of the 2:1 complexes show broad and intense O · H · O stretching absorptions in the 1500–200 cm −1 range which are slightly affected by the anion and are similar to that for type A acid salts of carboxylic acids. The skeletal vibrations of the betaine residue were identified by second derivative spectroscopy. Evidence based on the νCO vibration and deuteration suggests that the hydrogen bonds in [C 5 H 5 NCH 2 COO · H · OOCCH 2 NC 5 H 5 ] + A − are described by single minimum potentials; ν H = 940 cm −1 , ν H /ν D = 1.2. As betaines are widely distributed in plants and animal tissue and form complexes with strong hydrogen bonds, such bonds should be formed in biological systems.

X-ray, Fourier-transform infrared, 1H and 13C nuclear magnetic resonance, and PM3 studies of (N—H⋯N)+ and (O—H⋯O)– intramolecular hydrogen bonds in a complex of 1,8-bis(dimethylamino)naphthalene with maleic acid

The crystal structure of the title compound has been determined by X-ray analysis. The intramolecular hydrogen bond lengths are 2.606(3)A for the (NHN)+ bridge in protonated 1,8-bis(dimethylamino)naphthalene cation (DMAN+H) and 2.401(4)A for the (OHO)– bridge in the hydrogen maleate anion (HM–). The H-bonds are asymmetrical and not strictly linear: NHN, 157(3)° and OHO, 170(5)°. The geometries of the N—H⋯N and O—H⋯C bridges of the investigated cation and anion are dominated by the spherical repulsions of their constituent atoms.The overlapping bands in the absorbance IR spectra of potassium hydrogen (deuteron) maleate are separated in the second-derivative spectra. The strong mixing of the in-plane modes with skeletal modes in the hydrogen maleate ion causes a larger separation (Δν≈ 115 cm–1) of the ν(CO) bands in comparison with those in other type A acid salts containing intermolecular hydrogen bonds (Δν≈ 20–35 cm–1). The observed lack of solvent effect on the IR absorption suggests that the hydrogen bonds in tetrabutylammonium hydrogen maleate and 1,8-bis(dimethylamino)naphthalene hydrogen maleate are not extremely polarizable. 1H and 13C NMR chemical shifts of the investigated compound were measured and identified in two-dimensional (2D) experiments. The 1H NMR spectra show two narrow signals at ca. 19.5 and 18.7 ppm due to the OHO and NHN protons, respectively. The structural parameters of the cation and anion were also determined by quantum-mechanical calculations with the semiempirical MNDO-PM3 method.

Differences between the N·H·O and O·H·O hydrogen bonds in complexes of 2,6-dichloro-4-nitrophenol with pyridines and pyridine N-oxides

Abstract Complexes of five pyridines and nine pyridine N-oxides with 2,6-dichloro-4-nitrophenol (DCNP) in solution and the solid state were studied by Fourier transform IR and UV spectroscopy, by quantum-mechanical calculations with the semiempirical parametric method 3 (PM3) and by X-ray analysis. The crystals of the 1 : 1 complex of 4-methoxy-2,6-dimethylpyridine N-oxide with DCNP are monoclinic, space group P 2 1 n , a = 4.5936(5) A , b = 21.953(3) A , c = 15.664(2) A , β = 92.87(1)°, V = 1577.6(8) A 3 , Z = 4. The molecules of the complex are joined together by an N+OH⋯O− hydrogen bond with an O⋯O distance of 2.425(3) A, a CO− distance of 1.286(3) A and a (N+O)H⋯O− angle of 152.9°. The PM3 method predicts for all the investigated complexes two minima, the deeper one for B⋯HA complexes and the shallower one for the B+H⋯A− forms. For the 4-methylpyridine complex the N+H⋯O− distance is reproduced correctly but for the 4-methoxy-2,6-dimethylpyridine N-oxide complex the N+H⋯O− distance is too long. The predicted hydrogen-bond angles differ from the experimental values by more than 10°. In solid state complexes of pyridines the N⋯O distances and the broad absorption due to a protic vibration are not directly related to ΔpKa. This is due to the crystal packing forces. In solution the broad absorption varies with ΔpKa. A band in the 3500 cm−1 region due to the solvated phenol is present in all investigated complexes in solution. Absorption in the 3000−2000 cm−1 region of pyridine complexes is more intense than that of the pyridine N-oxides, in agreement with the difference in N⋯O and NO⋯O distances. The broad absorption in the spectra of pyridine complexes is more influenced by solvent effects than in the pyridine N-oxide complexes. The UV spectra of the pyridine complexes show two bands due to B⋯HA (305–315 nm) and B+H⋯A− (382–395 nm) forms. The UV spectra of complexes of pyridine N-oxides of intermediate strengths in CH2Cl2 are not combinations of the spectra of phenol and phenolate. The band in the intermediate position denotes that neither species close to phenol nor to phenoxide ion is present. In these complexes the proton is probably localized in a single minimum and the minimum moves from the donor to the acceptor or, what is more probable, reorganization of the solvent molecules around the complex is faster than the time range of UV spectroscopy. In acetonitrile the situation is quite different as two bands are present, in agreement with a prototropic equilibrium. Effects of solvent, concentration and stoichiometry on interactions of DCNP with pyridines and pyridine N-oxides are compared and discussed. An extended mechanism of the proton-transfer reaction is proposed.

X-ray, FT-IR and PM3 studies of hydrogen bonds in complexes of some pyridines with trifluoroacetic acid

Abstract The crystal structures of trifluoroacetic acid complexes with 4-NMe 2 -, 4-Me- and 4-CN-pyridines were determined by X-ray analysis; the NH⋯O bonds are 2.724(3), 2.702(4) and 2.587(5) A respectively. The H-bonds are nearly linear for 4-NMe 2 , 177(4)°; 4-Me, 177(4)°; and 4-CN, 174(6)°. IR spectra (Nujol) show continuous absorption, whose intensity decreases with elongation of the H-bond length. The continuous absorption is not observed in D 2 O spectra. The solid-state spectra in the 1700 cm −1 region are more complex than those in D 2 O; the characteristic overtones of the pyridine rings borrow intensity from the continuous absorption via Fermi resonance. The overtones indicate modified structure in the 1700 cm −1 region. The results of both diffraction and FT-IR experiments are comparable. The structural parameters of the complexes were also determined by quantum-mechanical calculations with the semiempirical MNDO—PM3 method. A solvent effect was taken into account using a self-consistent reaction field theory.

Investigation of B ⋯ HA ⇌ B+H ⋯ A− equilibrium in complexes of trifluoroacetic acid with pyridines in dichloromethane by second derivative infrared spectroscopy

Abstract The second derivative of FTIR spectra in the carbonyl—carboxyl region has been used in order to study the interaction of trifluoroacetic acid with eight R-pyridines in dichloromethane. In the case of the equimolar base—acid mixture, the following species (a) B · HA, (b) B · HA · HA, (c) B+H · A− and (d) B+H · A− · HA are recognized. All of the species are present in complexes of the medium strong pyridines (R = H or D, 3-Me and 4-Me). Two species (a) and (b) are found for complexes of the weakest, when R = 4-CN and 3-Br, and another two (c) and (d) for complexes of the strongest, when R = 3-NMe2 and 2,4,6-Me3, pyridines. Complete formation of the 1:1 complex requires an excess of pyridines. Fermi resonance of overtones due to pyridines and the acid with the continuous absorption is observed.

Hydrogen bonding and proton localization in complexes of carboxybetaines with phenols and carboxylic acids

Abstract Complexes of betaine (BET) with 2,6-dichloro-4-nitrophenol (DCNP), pentachlorophenol (PCP) and trifluoroacetic, trichloroacetic, dichloroacetic, chloroacetic and maleic acids and of pyridine betaine (PBET) with DCNP in solution and in the solid state were studied by UV and FTIR spectroscopies and X-ray analysis. The crystal of BET·DCNP is triclinic, space group P 1 , a = 7.1770(10) A , b = 10.001(2) A , c = 11.241(2) A , α = 108.81(3)°, β = 100.06(3)°, γ = 106.82(3)°, Z = 2; the final R value is 0.033 for 1871 observed reflections. Protonated betaine and 2,6-dichloro-4-nitrophenolate are linked by an O(2)Htctdot;O(1) hydrogen bond with an Otctdot;O distance of 2.424(3) A and the O(2)Htctdot;O(1) angle is 159(3)°. The broad absorption in the solid state FTIR spectra of the investigated complexes varies with ΔpKa, and is typical of complexes with strong hydrogen bonds. The UV spectra of phenol complexes in acetonitrile show a typical absorption for Btctdot;HA and B+Htctdot;A− species. In less polar dichloromethane, only molecular complexes are present. An exception is PBET·DCNP, where B+Htctdot;A− species appear in both solvents. The agreement between the UV and IR data is good.

Catalysis of hydrosilylation: Part XXXI. Functionalization of poly(methylhydro)siloxanes via hydrosilylation of allyl derivatives†

The synthesis of functional poly(methylhydro)siloxanes has been successfully performed by effective quantitative hydrosilylation of allyl derivatives (allyl phenyl ether, allyl glycidyl ether, allyl methacrylate, allyl chloride, allylamine) and 1-octene with poly(methylhydro)siloxanes catalyzed by platinum [Pt(PPh3)2(CH2=CH2), PtCl2(PPh3)2, H2PtCl6–cyclohexanone] and ruthenium (Ru3(CO)12) complexes. The products were isolated and characterized by 1H NMR, FT IR and GPC methods and can be regarded as examples of well-defined functionalized polysiloxanes with various practical applications.

FTIR studies of complexes of N-methylmorpholine betaine with phenols

Three types of crystalline complexes of N-methylmorpholine betaine (MMB) with phenols (1:1, 1:2, 2:1) were prepared and their FTIR spectra were studied as a function of the acidity of phenols. The variations of absorption in the 3000‐ 2000 and 1600‐ 400 cm 21 regions with pKa values of phenols in the 1:1 complexes reflect the formation of the molecular complex (A‐ H· · ·B) and hydrogen-bonded ion pair (A 2 · · ·HB þ ). In the 1:2 complexes the betaine carboxylate group is linked to two phenol molecules forming two different hydrogen bonds. The FTIR spectra are less affected by proton donor properties of phenol. In the 2:1 complex of MMB with picric acid two molecules of MMB are bridged by hydrogen bond and form a homoconjugated cation. The FTIR spectrum shows a broad (continuum) absorption in 1500‐ 400 cm 21 region, which suggests a strong hydrogen

FT-IR, UV—visible and X-ray studies of complexes of pyridine N-oxides with pentachlorophenol

Abstract The crystal structure of the 4-methoxy-2,6-dimethylpyridine N -oxide·pentachlorophenol complex has been determined by X-ray analysis. The O ··· O distance is 2.439(6) A, the OHO angle is 152.3° and the hydrogen-bonded proton is close to the phenol molecule. The FT-IR spectra of pentachlorophenol complexes with some substituted pyridine N -oxides in the solid state and seven aprotic solvents of different polarity (ϵ from 2.27 to 37.5) show a broad absorption. The broad absorption shows weak dependence upon solvent polarity and is classified as type (ii). UV spectra show that in the investigated complexes protons are not transferred from the phenol to the N -oxides. Formamide ( ϵ = 111) is a much stronger proton acceptor than the pyridine N -oxides. Pentachlorophenol in formamide is converted to the phenolate ion.

Evidence for a single minimum potential for hydrogen bonds of pyridine N-oxide complexes with dichloroacetic acid in dichloromethane

Abstract FTIR spectra of dichloracetic acid and its eight complexes with substituted pyridine N -oxides and N,N -dimethylaniline in dichloromethane-d 2 are reported. 4- N,N -dimethylaminopyridine N -oxides form two types of complexes with dichloroacetic acid; the acid interacts with NO or Me 2 N groups. The shape of the second derivative of absorption in the carbonyl region implies that the hydrogen bonds are described by a strongly asymmetrical quasi-single minimum potential. The situation with regard to the observed carbonyl frequencies as related to conformational equilibria is reviewed.