Evidence for the O-H⋅⋅⋅O=C Resonance-Assisted Hydrogen Bond in Tropolones and Quantification of its σ- and π-Components Using Molecular Tailoring Approach.

For a series of tropolones, the nature of the intramolecular O-H⋅⋅⋅O=C hydrogen bond closing the five-membered quasi-cycle was studied. Enhancement of conjugation in the hydrogen-bonded rotamer was revealed. Quantification of hydrogen bond energy in tropolones via the molecular tailoring approach yields values in the range from 15 to 20 kcal/mol suggesting that the intramolecular interaction in tropolones has nature of the resonance-assisted hydrogen bond.

Quantification of hydrogen bond energy based on equations using spectroscopic, structural, QTAIM-based, and NBO-based descriptors which calibrated by the molecular tailoring approach.

Context: Hydrogen bonds critically influence the structure and properties of both organic molecules and biomolecules, as well as supramolecular assemblies. For this reason, the development and elaboration of methods for quantitative assessment of hydrogen bond energy is an urgent challenge. In this study, using a large series of hydroxycarbonyl aliphatic compounds with the O‒H···O = C intramolecular hydrogen bond, a bank of hydrogen bond descriptors was created, including spectroscopic, structural, QTAIM-based, and NBO-based parameters.

Revealing the Reasons for Degeneration of Resonance-Assisted Hydrogen Bond on the Aromatic Platform: Calculations of Ortho-, Meta-, Para-Disubstituted Benzenes, and ()-()-Olefins.

The energies of the O-H∙∙∙O=C intramolecular hydrogen bonds were compared quantitatively for the series of ortho-disubstituted benzenes and -isomers of olefins via a molecular tailoring approach. It was established that the hydrogen bond energy in the former series is significantly less than that in the latter one. The reason for lowering the hydrogen bond energy in the ortho-disubstituted benzenes compared to the -isomers of olefins is the decrease in the π-contribution to the total energy of the complex interaction, in which the hydrogen bond is enhanced by the resonance effect.

Digitization of the electron shell the localized orbital locator formalism: trends in the size and electronegativity changes of atoms across the periodic table.

The parameters of the (3, -3) critical point in the topology of the localized orbital locator inside the electron shell reveal patterns that make it possible to recognize trends in the size, electronegativity, and ionization energy of atoms in the first four periods of the periodic table.

Molecular tailoring approach as tool for revealing resonance-assisted hydrogen bond: Case study of Z-pyrrolylenones with the NH⋯OС intramolecular hydrogen bond.

Both the experimental and calculated data reveal that a strong NH⋯OС intramolecular hydrogen bond closing the seven-membered quasi-cycle is formed in the Z-isomers of pyrrolylenones. Comparison of the NH⋯OС intramolecular hydrogen bonds energies in the pyrrolylenones, estimated via the molecular tailoring approach, with the similar data for reference malonaldehydes shows that the resonance-assisted hydrogen bonding occurs in both cases, the hydrogen bond energy being varied mainly within 10-20 kcal/mol. The combined application of function-based and molecular tailoring approaches makes it possible to decompose the NH⋯OС total hydrogen bond energy in the pyrrolylenones into the π- and σ-components.

Guide to tuning the chalcone molecular properties based on the push-pull effect energy scale created via the molecular tailoring approach.

Using the molecular tailoring approach, a total energy scale for the push-pull effect in the range from -40 to 100 kcal/mol is created for the wide series of neutral, charged and doubly charged compounds on the chalcone platform. Taking into account similar energy scale for hydrogen bonds, the strength of the push-pull effect is ranked in the seven categories, ranging from negative (anti-push-pull) to very weak and very strong push-pull effect. It is demonstrated that the molecular properties of chalcone can be tuned prior synthesis due to the created energy scale for the push-pull effect.

Localized orbital locator as a descriptor for quantification and digital presentation of lone pairs: benchmark calculations of 4-substituted pyridines.

The parameters of the (3,-3) critical point in the localized orbital locator topology near a heteroatom have been found to reflect the changes in the size, density and electron energy of the lone pair and correlate with the donor ability of the lone pair carrying heteroatom.

A molecular tailoring approach - a new guide to quantify the energy of push-pull effects: a case study on ()-3-(1-pyrrol-2-yl)prop-2-enones.

The molecular tailoring approach is recognized to be an efficient tool for quantifying the strength of the push-pull effect in molecules with internal charge transfer.

Acylacetylenes in multiple functionalization of hydroxyquinolines and quinolones.

The expected one-pot multiple functionalization of hydroxyquinolines and quinolones with acylacetylenes (20 mol% KOH, 5 equiv. HO, MeCN, 55-60 °C), which, according to the previous finding, might involve the addition of OH and NH-functions to the triple bond and insertion of acylacetylenes into the quinoline scaffold, retains mainly on the formation of chalcone-quinoline ensembles in up 99% yield. The higher functionalized quinolines can be obtained in a synthetically acceptable yield, when the above ensembles are treated with the second molecule of acylacetylenes.

KOBu/DMSO-Mediated α-C-H Vinylation of -Benzyl Ketimines with Acetylene Gas: Stereoselective Synthesis of (,)-2-Azadienes.

Several imines, readily derived from aryl methyl ketones and benzylamines, react with acetylene gas in KOBu/DMSO system to afford 2-azadienes stereoselectively. This new C-C bond constructing reaction involves, instead of the expected ethynylation of the C═N bond, the addition of azaallyl anions to the triple bond of acetylene.

Quantitative decomposition of resonance-assisted hydrogen bond energy in β-diketones into resonance and hydrogen bonding (π- and σ-) components using molecular tailoring and function-based approaches.

Using the molecular tailoring and function-based approaches allows one to divide the energy of the O─H⋯O═C resonance-assisted hydrogen bond in a series of the β-diketones into resonance and hydrogen bonding components. The magnitude of the resonance component is assessed as about 6 kcal mol . This value increases by ca.

Cyanoacetylenes as Triggers and Partners in KOH-Assisted Assemblies of Quinoline-Based Dihydropyrimido[1,2-]quinolin-3-ones on Water.

Arylcyanoacetylenes trigger the assembly of dihydropyrimido[1,2-]quinolin-3-ones in good to excellent yields on the platform of quinolines in the presence of KOH in aqueous media at room temperature. This green on-water methodology provides a simple one-pot access to a novel family of the pharmaceutically prospective compounds.

Study of spontaneous E/Z isomerization of bis[(Z)-cyanomethylidene]-diazapentacyclodienedicarboxylates by H, C, and N NMR spectroscopy, X-ray, and quantum chemical calculation data.

X-ray data show that the diethyl 6,13-bis[(Z)-cyanomethylidene]-5,5,14,14-tetramethyl-4,15-dioxa-7,12-diazapentacyclo[9.5.2.

Estimating the energy of intramolecular hydrogen bonds from H NMR and QTAIM calculations.

The values of the downfield chemical shift of the bridge hydrogen atom were estimated for a series of compounds containing an intramolecular hydrogen bond O-HO, O-HN, O-HHal, N-HO, N-HN, C-HO, C-HN and C-HHal. Based on these values, the empirical estimation of the hydrogen bond energy was obtained by using known relationships. For the compounds containing an intramolecular hydrogen bond, the DFT B3LYP/6-311++G(d,p) method was used both for geometry optimization and for QTAIM calculations of the topological parameters (electron density ρ and the density of potential energy V in the critical point of the hydrogen bond).

Experimental and theoretical study of the intramolecular C-H···N and C-H···S hydrogen bonding effects in the 1H and 13C NMR spectra of the 2-(alkylsulfanyl)-5-amino-1-vinylpyrroles: a particular state of amine nitrogen.

In the (1)H NMR spectra of the 1-vinylpyrroles with amino- and alkylsulfanyl groups in 5 and 2 positions, an extraordinarily large difference between resonance positions of the HA and HB terminal methylene protons of the vinyl group is discovered. Also, the one-bond (1)J(C(β),H(B)) coupling constant is surprisingly greater than the (1)J(C(β),H(A)) coupling constant in pyrroles under investigation, while in all known cases, there was a reverse relationship between these coupling constants. These spectral anomalies are substantiated by quantum chemical calculations.

Stereoselective tandem ring opening of imidazoles with electron-deficient acetylenes and water: synthesis of functionalized (Z,Z)-1,4-diaza-2,5-dienes.

1-Substituted imidazoles undergo exceptionally facile stereoselective ring opening under the influence of electron-deficient acetylenes and water (equimolar ratio of the reactants) in MeCN at 45-60 °C without any catalysts to afford functionalized (Z,Z)-1,4-diaza-2,5-dienes, (Z,Z)-propenylaminoethenylformamides, in up to 80% yields. The reaction is rationalized to proceed in a tandem manner via zwitterionic vinyl carbanions formed by nucleophilic addition of imidazole to the triple bond. The carbanionic center is then quenched with water followed by the rearrangement of the intermediate 2-hydroxy-3-alkenylimidazolines.

Structural peculiarities of configurational isomers of 1-styrylpyrroles according to 1Н, 13С and 15N NMR spectroscopy and density functional theory calculations: electronic and steric hindrance for planar structure.

Comparative analysis of the (1)Н and (13)С NMR data for a series of the E and Z-1-styrylpyrroles, E and Z-1-(1-propenyl)pyrroles, 1-vinylpyrroles and styrene suggests that the conjugation between the unsaturated fragments in the former compounds is reduced. This is the result of the mutual influence of the donor p-π and π-π conjugation having opposite directions. According to the NMR data combined with the density functional theory calculations, the Z isomer of 1-styrylpyrrole has essentially a nonplanar structure because of the steric hindrance.

Stereospecificity of (1) H, (13) C and (15) N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on (1) H chemical shifts.

In the (13) C NMR spectra of methylglyoxal bisdimethylhydrazone, the (13) C-5 signal is shifted to higher frequencies, while the (13) C-6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the (1) H-6 chemical shift and (1) J(C-6,H-6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the -CH═N- bond does not change. This paradox can be rationalized by the C-H⋯N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum-chemical calculations including Bader's quantum theory of atoms in molecules analysis.

Study of stereospecificity of 1H, 13C, 15N and 77Se shielding constants in the configurational isomers of the selenophene-2-carbaldehyde azine by NMR spectroscopy and MP2-GIAO calculations.

In the (1)H and (13)C NMR spectra of selenophene-2-carbaldehyde azine, the (1)H-5, (13)C-3 and (13)C-5 signals of the selenophene ring are shifted to higher frequencies, whereas those of the (1)H-1, (13)C-1, (13)C-2 and (13)C-4 are shifted to lower frequencies on going from the EE to ZZ isomer or from the E moiety to the Z moiety of EZ isomer. The (15)N chemical shift is significantly larger in the EE isomer relative to the ZZ isomer and in the E moiety relative to the Z moiety of EZ isomer. A very pronounced difference (60-65 mg/g) between the (77)Se resonance positions is revealed in the studied azine isomers, the (77)Se peak being shifted to higher frequencies in the ZZ isomer and in the Z moiety of EZ isomer.

GIAO, DFT, AIM and NBO analysis of the N-H...O intramolecular hydrogen-bond influence on the 1J(N,H) coupling constant in push-pull diaminoenones.

In the series of diaminoenones, large high-frequency shifts of the (1)H NMR of the N-H group in the cis-position relative to the carbonyl group suggests strong N-H...

Study of conformations and hydrogen bonds in the configurational isomers of pyrrole-2-carbaldehyde oxime by 1H, 13C and 15N NMR spectroscopy combined with MP2 and DFT calculations and NBO analysis.

The (1)H, (13)C and (15)N NMR studies have shown that the E and Z isomers of pyrrole-2-carbaldehyde oxime adopt preferable conformation with the syn orientation of the oxime group with respect to the pyrrole ring. The syn conformation of E and Z isomers of pyrrole-2-carbaldehyde oxime is stabilized by the N-H..

Theoretical study of bifurcated hydrogen bonding effects on the 1J(N,H), 1hJ(N,H), 2hJ(N,N) couplings and 1H, 15N shieldings in model pyrroles.

According to the density functional theory calculations, the X...

Pronounced stereospecificity of (1)H, (13)C, (15)N and (77)Se shielding constants in the selenophenyl oximes as shown by NMR spectroscopy and GIAO calculations.

In the (1)H and (13)C NMR spectra of 1-(2-selenophenyl)-1-alkanone oximes, the (1)H, the (13)C-3 and (13)C-5 signals of the selenophene ring are shifted by 0.1-0.4, 2.

Comparative analysis of 13C shielding constants stereospecificity in the silicon and germanium derivatives of acetylenic aldehyde and ketone oximes based on the 13C NMR spectroscopy and GIAO calculations.

In the acetylenic aldehyde oximes with substituents containing silicon and germanium, the (13)C NMR signal of the C-2 carbon of triple bond is shifted by 3.5 ppm to lower frequency and that of the C-3 carbon is moved by 7 ppm to higher frequency on going from E to Z isomer. A greater low-frequency effect of 5.

C-H...N and C-H...O intramolecular hydrogen bonding effects in the 1H, 13C and 15N NMR spectra of the configurational isomers of 1-vinylpyrrole-2-carbaldehyde oxime substantiated by DFT calculations.

According to the (1)H, (13)C and (15)N NMR spectroscopic data and DFT calculations, the E-isomer of 1-vinylpyrrole-2-carbaldehyde adopts preferable conformation with the anti-orientation of the vinyl group relative to the carbaldehyde oxime group and with the syn-arrangement of the carbaldehyde oxime group with reference to the pyrrole ring. This conformation is stabilized by the C-H..