Concerning lone-pair stereospecificity of intramolecular OH hydrogen bonds to oxygen and sulfur in solution

1987 ◽  
Vol 65 (5) ◽  
pp. 908-914 ◽  
Author(s):  
Ted Schaefer ◽  
David M. McKinnon ◽  
Rudy Sebastian ◽  
James Peeling ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Coupling Constants ◽  
Boat Conformation ◽  
Lone Pairs ◽  
Saturated Ring ◽  
Hydroxyl Protons ◽  
Lone Pair Electrons

The 1H nuclear magnetic resonance spectra for CCl4 solutions are analyzed for 2-(thioethyl)phenol, 2,3-dimethoxyphenol, and 8-hydroxythiochroman. The chemical shifts of the hydroxyl protons in these compounds, in 2,3-dihydroxyanisole, and 2-hydroxybenzyl methyl ether are discussed in terms of stereospecific intramolecular OH hydrogen bonds to lone-pair electrons on oxygen and sulfur. The O—H … O hydrogen bonds can be adequately discussed in terms of equivalent lone pairs on oxygen. There is very little difference between the hydrogen bond energies for 2,3-dihydroxyanisole and 2,3-dimethoxyphenol. In the latter the central hydrogen bonded methoxy group lies nearly perpendicular to the ring plane. The O—H … S hydrogen bonds are best described in terms of nonequivalent, 3s and 3p, lone pairs on sulfur. It is estimated that an O—H … H 3s hydrogen bond is at least 8 kJ/mol weaker than an O—H … 3p hydrogen bond. The former is predominant in the thiochroman derivative and the latter in the thioethylphenol, in which the thioethyl group prefers a plane perpendicular to the benzene ring. The long-range benzylic coupling constants in the thiochroman derivative indicate inversion of the saturated ring between distorted half-chair conformations. The boat conformation can be ruled out.

N.M.R. spectra and stereochemistry of the bipyridyls. III. 2,2'-Bipyridyl and dimethyl derivatives, 3,3'- bipyridyl, and 4,4' - bipyridyl

1967 ◽  
Vol 20 (6) ◽  
pp. 1227 ◽  
Author(s):  
TM Spotswood ◽  
CI Tanzer
Keyword(s):  
Hydrogen Bonding ◽  
Electrostatic Field ◽  
Field Effect ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Diamagnetic Anisotropy ◽  
Equal Importance ◽  
Nitrogen Lone Pair ◽  
Lone Pair Electrons ◽  
Derivatives Of

The analysis of the n.m.r, spectra of 2,2?-, 3,3?-, and 4,4?-bipyridyl and three dimethyl-2,2?-bipyridyls is reported and the factors determining the relative chemical shifts of the ring protons and methyl groups in several solvents are discussed. The diamagnetic anisotropy of the neighbouring ring and electrostatic field effect of the nitrogen lone pair electrons are shown to be of roughly equal importance for derivatives of 2,2?-bipyridyl except in hydrogen bonding solvents. Attenuation of the electrostatic field effect in polar, and particularly in hydrogen bonding solvents, is established for 4- picoline, and for the bipyridyls, and this effect is responsible for striking changes in the spectrum of 2,2?-bipyridyl in hydrogen bonding solvents. An approximate interplanar angle of 58� is derived for 3,3?- dimethyl-2,2?-bipyridyl, and 2,2?-bipyridyl and its 4,4?- and 5,5?- dimethyl derivatives appear to be trans coplanar in all solvents. 3,3?- Bipyridyl and 4,4?-bipyridyl are probably highly twisted in all solvents, or alternatively, behave as essentially free rotors. The predicted conformations are in good agreement with the electronic spectral data.

Elektronendichte und chemische Verschiebung der Styryldiazin- und Diazaphenanthrenprotonen / Electrondensity and Proton Chemical Shift of Styryldiazines and Diazaphenanthrenes

1972 ◽  
Vol 27 (2) ◽  
pp. 310-319
Author(s):  
H.-H. Perkampus ◽  
Th. Bluhm ◽  
J. Knop
Keyword(s):  
Ring Current ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Current Effect ◽  
Electron Densities ◽  
Paramagnetic Effect ◽  
Nitrogen Lone Pair ◽  
Chemische Verschiebung ◽  
Lone Pair Electrons ◽  
Proton Chemical Shifts

AbstractProton chemical shifts in styryldiazines and diazaphenanthrenes linearly correlate with SCF-π-electron densities of the attached carbon atom and with the electron densities of the hydrogen atom (calculated by the CNDO/2 method). The observed deviations from linearity are discussed in terms of ring current effect, steric effects and the paramagnetic effect of the nitrogen lone pair electrons. An appreciable weakening of ring current is found for diazaphenanthrenes with two adjacent N-atoms. Under the same condition the paramagnetic effect on ortho-hydrogens is increased.

Neue Untersuchung über Inhaltsstoffe aus Aloe-und Rhamnus-Arten, XV [1] Homonataloin A und B aus Aloe lateritia: Reindarstellung, Konstitutions-und Konfigurationsaufklärung der Diastereomeren / A New Investigation on Constituents of Aloe and Rhamnus Species, XV [1] Hom onataloins A and B from Aloe lateritia: Isolation, Structure and Configurational Determ ination of the Diastereomers

1991 ◽  
Vol 46 (3-4) ◽  
pp. 177-182 ◽  
Author(s):  
Hans-W. Rauwald ◽  
Deo-D. Niyonzima
Keyword(s):  
Chemical Shifts ◽  
Optical Rotation ◽  
Coupling Constants ◽  
Cd Spectra ◽  
Large Coupling ◽  
H Nmr ◽  
Leaf Exudate ◽  
Hydroxyl Protons ◽  
Nmr Signals ◽  
C Nmr

From the leaf exudate of Aloe lateritia ENGLER the C-glucosyl com pounds homonataloin, aloeresin A and aloesin (synon. aloeresin B) were isolated together with the anthraquinone nataloeem odin-8-methylether and spectroscopically identified. Hom onataloin, widely distributed in Aloe species, was separated into homonataloin A and B by combined TLC and DCCC. In their 1 D and 2D 1H NMR spectra only the shifts of the 2′-hydroxyl protons of both glucosyl residues differ significantly, indicative of 10 S (A) resp. 10 S (B) configurations. In both com pounds the anthrone is in β-position of the D-glucopyranosyl, as determined by the large coupling constants of the anomeric protons. The 13C NMR signals are unambiguously assigned by the use of DEPT, APT and gated-decoupling methods. Only the chemical shifts of C -11 and C -14 show significant differences between both diastereomers due to the adjacent 2′-sugar hydroxyls. The two homonataloins differ mostly in optical rotation and circulardichroism due to different configurations at C - 10 of the anthrone part. The absolute configurations of the diastereomers are determined by correlation of their CD spectra with the CD spectra of the structural analogues 7-hydroxyaloins A and B, which shows that hom onataloin A is the 10 S, 1′S-compound and that homonataloin B has 10 R, 1′S-configuration.

scholarly journals 2-Amino-6-{[(6-chloropyridin-3-yl)methyl](ethyl)amino}-1-methyl-5-nitro-4-phenyl-1,4-dihydropyridine-3-carbonitrile ethanol monosolvate

2012 ◽  
Vol 68 (4) ◽  
pp. o1146-o1146
Author(s):  
Chuan-Wen Sun ◽  
Yan-Xia Chen ◽  
Tian-Yan Liu
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Title Compound ◽  
Crystal Packing ◽  
Boat Conformation ◽  
Methyl Ethyl ◽  
Compound C ◽  
Dihydropyridine Ring

In the title compound, C21H21ClN6O2·C2H6O, a member of the insecticidal active neonicotinoid group of compounds, the 1,4-dihydropyridine ring adopts a boat conformation. An intramolecular C—H...O hydrogen bond occurs while the components are linked by an N—H...O interaction. The crystal packing is stablized by O—H...N hydrogen bonds and C—H...O interactions.

Molecular dynamics simulations of N-methylacetamide (NMA) in water by the ABEEM/MM model

2009 ◽  
Vol 87 (12) ◽  
pp. 1738-1746 ◽  
Author(s):  
Ping Qian ◽  
Li-Nan Lu ◽  
Zhong-Zhi Yang
Keyword(s):  
Molecular Dynamics ◽  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Potential Model ◽  
Lone Pair ◽  
Static Properties ◽  
Range Interaction ◽  
Hydrogen Bond Interaction ◽  
Lone Pair Electron ◽  
Dynamics Simulations

The N-methylacetamide (NMA) is a very interesting kind of compound and often serves as a model of the peptide bond. The interaction between NMA and water provides a convenient prototype for the solvation of peptides in aqueous solutions. We have carried out molecular dynamics (MD) simulations of a NMA molecule in water under 1 atm and 298 K. The simulations make use of the newly developed NMA–water fluctuating charge ABEEM/MM potential model ( Yang, Z. Z.; Qian, P. J. Chem. Phys. 2006, 125, 064311 ), which is based on the combination of the atom-bond electronegativity equalization method (ABEEM) and molecular mechanics (MM). This model has been successfully applied to NMA–water gas clusters, NMA(H2O)n (n = 1–6), and accurately reproduced many static properties. For the NMA–water ABEEM/MM potential model, two characters must be emphasized in the simulations. Firstly, the model allows the charges in system to fluctuate, responding to the ambient environment. Secondly, for two major types of intermolecular hydrogen bonds, which are the hydrogen bond forming between the lone-pair electron on amide oxygen and the water hydrogen, and the one forming between the lone-pair electron on water oxygen and the amide hydrogen, we take special treatments in describing the electrostatic interaction by the use of the parameters klpO=,H and klpO–,HN–, respectively, which explicitly describe the short-range interaction of hydrogen bonds in the hydrogen bond interaction region. All sorts of properties have been studied in detail, such as, radial distribution function, energy distribution, ABEEM charge distribution and dipole moment, and so on. These simulation results show that the ABEEM/MM-based NMA–water potential model appears to be robust, giving the solution properties in excellent agreement with other dynamics simulations on similar systems.

Temperature dependence of chemical shifts of protons in hydrogen bonds. Experimental evidence on an intramolecular hydrogen bond

1968 ◽  
Vol 46 (17) ◽  
pp. 2865-2868 ◽  
Author(s):  
T. Schaefer ◽  
G. Kotowycz
Keyword(s):  
Hydrogen Bond ◽  
Carbon Tetrachloride ◽  
Chemical Shift ◽  
Hydrogen Bonds ◽  
Temperature Dependence ◽  
Intramolecular Hydrogen Bond ◽  
Chemical Shifts ◽  
Hydroxyl Proton ◽  
Intramolecular Hydrogen ◽  
Strong Intramolecular Hydrogen Bond

A temperature dependence of the chemical shift of the hydroxyl proton in the strong intramolecular hydrogen bond in 3,5-dichlorosalicylaldehyde is observed in carbon tetrachloride and benzene-d6 solutions. Its magnitude of 0.25 to 0.30 × 10−2 p.p.m. per ° C over a range of 100 °C is in agreement with the model described by Muller and Reiter (1).

Mechanisms of long-range 13C, 13C spin–spin coupling in thioanisole and its derivatives. Conformational applications

1988 ◽  
Vol 66 (5) ◽  
pp. 1229-1238 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner
Keyword(s):  
Hydrogen Bond ◽  
Long Range ◽  
Intermolecular Hydrogen Bond ◽  
Lone Pair ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hydroxyl Group ◽  
Trans Orientation ◽  
Solvent Molecules ◽  
Spin Spin Coupling

The 13C nuclear magnetic resonance chemical shifts and the long-range 13C,13C spin–spin coupling constants are reported for 23 thioanisole derivatives enriched in 13C at the methyl position. For para and meta substituted thioanisole derivatives, nJ(C,C) (n being the formal number of bonds intervening between the coupled nuclei) can be related to functions of the angle by which the thiomethyl group twists out of the aromatic plane. For n = 3,4,5, the ensuing relationships yield estimates of the twofold barriers to rotation about the C(1)—S bond. The barrier is lower in ethyl phenyl sulfide than in thioanisole derivatives. Complications arise for ortho substituted thioanisole derivatives but estimates of the torsional motion about the C(1)—S bond can be obtained from the observed nJ(C,C). Among the complications is the expected fact that 3J(C,C), which is shown to be larger in the cis than the trans orientation of the intervening bonds ("anti-Karplus" behaviour), is perturbed by the substituent attached to the coupled nucleus. It is confirmed that in 2-hydroxythioanisole the thiomethyl group is oriented effectively perpendicular to the benzene plane, attributable to a stereospecific hydrogen bond between the hydroxyl group and the 3p lone-pair on the sulfur atom. In acetone-d6 solution, an equilibrium exists between this conformation and one in which an intermolecular hydrogen bond exists with solvent molecules. In the latter, the thiomethyl group prefers a coplanar orientation. In 2-aminothioanisole, the thiomethyl group twists out of the plane by about 60° so as to optimize the N—H … 3p interaction. This twist angle is changed very little in acetone-d6 solution because the second N—H bond can hydrogen bond to the solvent molecules without disrupting the intramolecular N—H … 3p interaction. It is also shown that the chemical shift of the 13C nucleus in the methyl group is a good conformational indicator in meta and para substituted thioanisoles. Therefore it can be used as such for molecules in which nJ(C,C) is difficult to find, in 1,4-dithiomethylbenzene, for example.

scholarly journals The crystal structures and Hirshfeld surface analysis of 6-(naphthalen-1-yl)-6a-nitro-6,6a,6b,7,9,11a-hexahydrospiro[chromeno[3′,4′:3,4]pyrrolo[1,2-c]thiazole-11,11′-indeno[1,2-b]quinoxaline] and 6′-(naphthalen-1-yl)-6a′-nitro-6′,6a′,6b′,7′,8′,9′,10′,12a′-octahydro-2H-spiro[acenaphthylene-1,12′-chromeno[3,4-a]indolizin]-2-one

2019 ◽  
Vol 75 (10) ◽  
pp. 1519-1524
Author(s):  
G. Foize Ahmad ◽  
A. Syed Mohammed Mujaheer ◽  
M. NizamMohideen ◽  
M. Gulam Mohamed ◽  
V. Viswanathan
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Chair Conformation ◽  
Piperidine Ring ◽  
Thiazole Ring ◽  
Boat Conformation ◽  
Pyran Ring ◽  
Axis Direction ◽  
Π Interactions ◽  
Spiro Derivatives

The title compounds, 6-(naphthalen-1-yl)-6a-nitro-6,6a,6 b,7,9,11a-hexahydrospiro[chromeno[3′,4′:3,4]pyrrolo[1,2-c]thiazole-11,11′-indeno[1,2-b]quinoxaline], C37H26N4O3S, (I), and 6′-(naphthalen-1-yl)-6a′-nitro-6′,6a′,6b′,7′,8′,9′,10′,12a′-octahydro-2H-spiro[acenaphthylene-1,12′-chromeno[3,4-a]indolizin]-2-one, C36H28N2O4, (II), are new spiro derivatives, in which both the pyrrolidine rings adopt twisted conformations. In (I), the five-membered thiazole ring adopts an envelope conformation, while the eight-membered pyrrolidine-thiazole ring adopts a boat conformation. An intramolecular C—H...N hydrogen bond occurs, involving a C atom of the pyran ring and an N atom of the pyrazine ring. In (II), the six-membered piperidine ring adopts a chair conformation. An intramolecular C—H...O hydrogen bond occurs, involving a C atom of the pyrrolidine ring and the keto O atom. For both compounds, the crystal structure is stabilized by intermolecular C—H...O hydrogen bonds. In (I), the C—H...O hydrogen bonds link adjacent molecules, forming R 2 2(16) loops propagating along the b-axis direction, while in (II) they form zigzag chains along the b-axis direction. In both compounds, C—H...π interactions help to consolidate the structure, but no significant π–π interactions with centroid–centroid distances of less than 4 Å are observed.

Protonation and microwave-assisted heating induced excitation of lone-pair electrons in graphitic carbon nitride for increased photocatalytic hydrogen generation

2019 ◽  
Vol 7 (35) ◽  
pp. 20223-20228 ◽  
Author(s):  
Dandan Wu ◽  
Shaonian Hu ◽  
Hongyun Xue ◽  
Xiaojuan Hou ◽  
Haiwei Du ◽  
...  
Keyword(s):  
Carbon Nitride ◽  
Hydrogen Generation ◽  
Lone Pair ◽  
Graphitic Carbon ◽  
Graphitic Carbon Nitride ◽  
Microwave Assisted ◽  
Photocatalytic Hydrogen Generation ◽  
Lone Pairs ◽  
Lone Pair Electrons ◽  
Generation Activity

Graphitic carbon nitride (g-C3N4) with pronounced excitation of lone pairs enhances its photocatalytic hydrogen (H2) generation activity.

Correspondence: Hydrogen Bond to Gold? 1H NMR is Not a Proof of Hydrogen Bonds in Transition Metal Complexes

2018 ◽  
Author(s):  
Jan Vícha ◽  
Cina Foroutan-Nejad ◽  
Michal Straka
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Chemical Shifts ◽  
X Ray ◽  
Structure And Dynamics ◽  
Hydrogen Bonding Interactions ◽  
Overall Stability ◽  
Gold Compounds ◽  
C Nmr

Illusive Au<sup>I/III</sup>···H hydrogen bonds and their effect on structure and dynamics of molecules have been a matter of debate. While a number of X-ray studies reported gold compounds with short Au<sup>I/III</sup>···H contacts, a solid spectroscopic evidence for Au<sup>I/III</sup>···H bonding has been missing. Recently<a></a><a>, Bakar <i>et al.</i></a> (NATURE COMMUNICATIONS 8:576) reported compound with four short Au···H contacts (2.61­–2.66 Å; X-ray determined). Assuming the central cluster be [Au<sub>6</sub>]<sup>2+</sup>and observing the <sup>1</sup>H (<sup>13</sup>C) NMR resonances at relevant H(C) nuclei deshielded with respect to precursor compound, the authors concluded with reservations that <i>“the present Au···H–C interaction is a kind of “hydrogen bond”, where the [Au<sub>6</sub>]<sup>2+</sup>serves as an acceptor”</i>. Here, we show that the Au<sub>6</sub>cluster in their compound bears negative charge and the Au···H contacts lead to a weak (~1 kcal/mol) auride···hydrogen bonding interactions, though unimportant for the overall stability of<b></b>the molecule. Additionally, computational analysis of NMR chemical shifts reveals that the deshielding effects at respective hydrogen nuclei are not directly related to Au···H–C hydrogen bonding .

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