Molecular complexes of the pyridines and quinolines N-oxides styryl derivatives with the Brønsted-Lowry acids
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Brønsted–Lowry acid–base theory
(1)H NMR chemical shifts have been obtained in the solvents deuterochloroform and dimethyl sulfoxide. The difference in the chemical shifts of an OH or NH group in these two solvents, Δδ = δ(DMSO) - δ(CDCl3), can be converted into the hydrogen bond acidity, A, of the group using the equation A = 0.0065 + 0.133Δδ. The NMR A value, ANMR, can be used as a quantitative assessment of intramolecular hydrogen bonding. We list values of Δδ and ANMR for 55 compounds containing an OH group and 60 compounds with an NH group. For the hydroxy compounds, if A > 0.5 then the OH group is not part of an intramolecular hydrogen bond, but if A < 0.1 then the OH group forms part of an intramolecular hydrogen bond. For NH compounds, if A > 0.16 the NH group is not part of an intramolecular hydrogen bond, and if A < 0.05 the NH group is part of an intramolecular hydrogen bond. No comparison compounds are needed, and the method is extremely simple. We further show how it is possible to relate intramolecular hydrogen bonding to the actual effect on values of a number of physicochemical, environmental, and biochemical properties.
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Abstract Solute descriptors characterizing major interactions in solution are accessible based on quantitative structure-property relationships (QSPR). Parameters of such relationships should be additive for functional groups. Because added parameters of monools describing molecular interaction do not meet the experimentally found intermolecular interaction parameters of diols and triols, it is assumed that intramolecular hydrogen bonding is responsible for these deviations. In this paper the intramolecular interactions in several diols are illuminated by IR measurements. Particularly, the influence of intramolecular hydrogen bonding on the absorbances of the OH groups is subject of investigation. Two conclusions can be drawn from the results: The terminal OH groups, which underlie an OH–OH interaction, also change their absorbance intensity in comparison to the free OH band. Secondly, the intermolecular interaction potential is strongly affected by intramolecular hydrogen bonding. The first observation is tentatively quantified as well as the position of the equilibrium between intramolecularly bonded and free diols.
Absorbance
Intermolecular interaction
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Facile protonation of α-octabutoxyphthalocyaninato zinc(II) (Zn(OBu)8Pc) occurs to afford up to tetra-protonated species stabilized by intramolecular hydrogen bonding, resulting in positive shifts of the reduction potentials of Zn(OBu)8PcHnn+ (n = 1–4) with increasing the number of protons attached to facilitate electron-transfer reduction.
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The intramolecular hydrogen-bonding energies for eighteen molecules were calculated based on the substitution method, and compared with those predicted by the cis-trans method. The energy values obtained from two methods are close to each other with a correlation coefficient of 0.96. Furthermore, the hydrogen-bonding energies based on the substitution method are consistent with the geometrical features of intramolecular hydrogen bonds. Both of them demonstrate that the substitution method is capable of providing a good estimation of intramolecular hydrogen-bonding energy.
Substitution (logic)
Bond energy
Low-barrier hydrogen bond
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Proton NMR
Amide
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Abstract The hydrogen‐bonded structures of Ac‐Gly‐ L ‐Ala‐Gly‐NHMe have been studied by theoretical conformational analysis. The geometric parameters and energies of stable forms with various combinations of 3 → 1 and 4 → 1 type hydrogen bonds have been calculated. The stable conformations found can be used as canonical forms in the investigation of linear and cyclic peptide compounds with intramolecular hydrogen bonds.
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Abstract The ir‐spectra in the NH stretching region of Piv‐Pro‐NHMe and Boc‐Pro‐NHMe have been studied in carbon tetrachloride and chloroform solutions over a wide range of concentrations. Based on the concentration dependence of the NH stretching bands, it has been shown that the characteristic NH stretching band due to the C 7 intramolecular hydrogen bond is around 3335 cm −1 . Intermolecular hydrogen bonding also occurs to a small extent in these peptides, giving rise to a slight concentration dependence of the NH stretching bands. The band around 3335 cm −1 need not necessarily be due to C 7 hydrogen bonds alone as proposed by Tsuboi et al. or to intermolecular hydrogen bonding alone as proposed by Maxfield et al.; this conclusion is supported by studies on Boc‐Leu‐NHMe, which undergoes only intermolecular hydrogen bonding. We have shown that Z‐Aib‐Aib‐OMe and Z‐Aib‐Ala‐OMe form C 7 intramolecular hydrogen bonds in addition to C 5 intramolecular hydrogen bonds. The present studies also show that all the peptides studied exist in more than one conformation in solution.
Low-barrier hydrogen bond
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Low-barrier hydrogen bond
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Journal of the Chemical Society Faraday Transactions 1 Physical Chemistry in Condensed Phases (1986)
Infrared spectral studies of the hydrogen-bonding behaviour of aminoethanol and aminopropanols have revealed that they form the strongest intramolecular hydrogen bonds among the substituted alcohols X(CH2)2,3,4OH where X = F, Cl, Br, I, OH, OCH3I, NR2(RH, alkyl) in a given series, establishing the importance of basicity in the hydrogen-bonding interaction. Strong intramolecular hydrogen bonding was found to reduce considerably their association tendency so that there were large amounts of intramolecularly hydrogen-bonded species in concentrated solution. The limited numbers of associated species formed were largely composed of closed dimers, whose nature depended on the strength of intramolecular hydrogen-bond. In dimethylaminoethanol and 3-aminopropanol, the dimers involved the participation of nitrogen so that fairly large ring dimers (ten- and twelve-membered, respectively) were formed. In the case of diethylaminopropanol, since the intramolecular hydrogen bond was very strong, the intermolecular association was limited to small amounts of free hydroxy monomers.
Low-barrier hydrogen bond
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Low-barrier hydrogen bond
Acceptor
Proton NMR
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