Theoretical insights into excited‐state process for the novel 2,3‐bis[(4‐diethylamino‐2‐hydroxybenzylidene)amino]but‐2‐enedinitrile system
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Abstract In this present work, we clarify the excited‐state intramolecular proton transfer (ESIPT) mechanism for 2,3‐bis[(4‐diethylamino‐2‐hydroxybenzylidene)amino]but‐2‐enedinitrile (BDABE) system. We present the fact that excited‐state single proton transfer can occur along with one hydrogen bond, even though BDABE form consists of two intramolecular hydrogen bonds. Based on the density functional theory and time‐dependent density functional theory methods, we theoretically investigate and elaborate the excited‐state intramolecular dual hydrogen‐bonding interactions. By simulating the electrostatic potential surface, we verify the formation of dual intramolecular hydrogen bonds for BDABE molecule in the S 0 state. Furthermore, comparing the primary bond lengths and bond angles as well as the infrared vibrational spectra, we find that the double hydrogen bonds should be strengthened in the S 1 state. When it comes to photoexcitation process, we discover the charge redistribution around hydrogen bonding moieties. The increased electronic density around proton acceptor plays the important roles in strengthening hydrogen bonds and in facilitating ESIPT reaction. In view of the possible ESIPT reaction paths (i.e., stepwise and synchronization double proton transfer) for BDABE molecule, we explored the S 0 ‐state and S 1 ‐state potential energy curves. This work explains experimental results and further clarifies the excited‐state behaviors for BDABE system.Keywords:
Photoexcitation
Potential energy surface
(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.
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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.
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Low-barrier hydrogen bond
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Proton NMR
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