Concerning the conformational preferences of the 2-cyano derivatives of oxane, thiane, and selenane

2010 ◽  
Vol 88 (8) ◽  
pp. 831-838 ◽  
Author(s):  
Michael H. Benn ◽  
Yan Yan Huang ◽  
Frank Johannsen ◽  
Michael O’Reilly ◽  
Masood Parvez ◽  
...  
Keyword(s):  
Bond Length ◽  
Cyano Group ◽  
Lone Pair ◽  
Nbo Analysis ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Model Compounds ◽  
Conformational Preferences ◽  
Lone Pair Electrons ◽  
Derivatives Of

This paper investigates the origin of the anomalous anomeric effect in merosinigrin, a 2-cyanothiane in which the cyano group is axial as expected for the anomeric effect, but in which bond distances are opposite to that expected from the nS→[Formula: see text] orbital interaction, which underlies the classical anomeric effect. The model compounds, 2-cyanooxane, 2-cyanothiane, and 2-cyanoselenane, were synthesized and studied both experimentally and computationally. Both the thia and selena systems displayed an even higher preference for the axial conformation than the oxa system but also exhibited the bond length anomalies found previously in merosinigren. Natural bond order (NBO) analysis of the B3LYP/6–311+G(3df,2p) wave functions of the axial and equatorial forms of the three systems confirmed a weakening of the n→σ* orbital interaction in the O, S, and Se series, and a strengthening of a σ–π*(CN) interaction that explains the bond length reversals observed in the S and Se systems. It also revealed a new mechanism, n→π*, namely, a through-space interaction between the nonbonded lone pair electrons of the heteroatom and the π* orbital of the cyano group, which selects for the axial conformation.

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.

scholarly journals Bond-length distributions for ions bonded to oxygen: metalloids and post-transition metals

2018 ◽  
Vol 74 (1) ◽  
pp. 63-78 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Transition Metal ◽  
Metal Ions ◽  
Bond Length ◽  
Coordination Number ◽  
Lone Pair ◽  
Transition Metal Ions ◽  
Length Variation ◽  
Coordination Polyhedra ◽  
Bond Lengths ◽  
Lone Pair Electrons

Bond-length distributions have been examined for 33 configurations of the metalloid ions and 56 configurations of the post-transition metal ions bonded to oxygen, for 5279 coordination polyhedra and 21 761 bond distances for the metalloid ions, and 1821 coordination polyhedra and 10 723 bond distances for the post-transition metal ions. For the metalloid and post-transition elements with lone-pair electrons, the more common oxidation state between n versus n+2 is n for Sn, Te, Tl, Pb and Bi and n+2 for As and Sb. There is no correlation between bond-valence sum and coordination number for cations with stereoactive lone-pair electrons when including secondary bonds, and both intermediate states of lone-pair stereoactivity and inert lone pairs may occur for any coordination number > [4]. Variations in mean bond length are ∼0.06–0.09 Å for strongly bonded oxyanions of metalloid and post-transition metal ions, and ∼0.1–0.3 Å for ions showing lone-pair stereoactivity. Bond-length distortion is confirmed to be a leading cause of variation in mean bond lengths for ions with stereoactive lone-pair electrons. For strongly bonded cations (i.e. oxyanions), the causes of mean bond-length variation are unclear; the most plausible cause of mean bond-length variation for these ions is the effect of structure type, i.e. stress resulting from the inability of a structure to adopt its characteristic a priori bond lengths.

Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones — Evidence for "exo-anomeric" interactions

2006 ◽  
Vol 84 (4) ◽  
pp. 685-691 ◽  
Author(s):  
Melissa L Trapp ◽  
John F Wojcik ◽  
Walter W Zajac, Jr. ◽  
B Mario Pinto
Keyword(s):  
Dft Calculations ◽  
Ab Initio ◽  
High Energy ◽  
The Other ◽  
Carbonyl Carbon Atom ◽  
Torsional Angle ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Orbital Interactions ◽  
Conformational Preferences

The conformational analysis of 2-phenylsulfinylcyclohexanone by ab initio density functional calculations is described. Six conformations corresponding to axial/equatorial isomers and rotation about the exocyclic C2—S bond in each of the RR or RS diastereomers were calculated and the results were examined in terms of relative energies, electrostatic interactions, orbital interactions, and geometrical variations. The global minimum conformation was the RS isomer that positioned the phenylsulfinyl moiety in an equatorial orientation and the sulfinyl oxygen in an anti orientation with respect to the carbonyl carbon atom. Of the other three low energy conformations, only one had a gauche arrangement of these atoms, and only in one of the four lower energy conformations was evidence found for a S-O(–)···C(+)-O electrostatic interaction. In contrast, the results were consistent with the operation of nS → [Formula: see text] stabilizing orbital interactions. Further support for this hypothesis was obtained from the increased C=O bond lengths in these four conformations relative to the other conformations, and by the torsional angle distortion away from ideal geometry, presumably to maximize the stabilizing orbital interaction. We propose that this conformational preference is a manifestation of a generalized exo-anomeric effect. The longer C2—S bond in the axial isomers was also interpreted in terms of a stabilizing πC=O → [Formula: see text] interaction, analogous to an endo-anomeric interaction. Comparison of the computational results to available experimental data on the conformational equilibrium of each diastereomer in solution suggests which conformers are present in each of the equilibria. The available data for the solid state indicate that the RR and RS isomers both crystallize in high energy conformations, stabilized by intermolecular interactions.Key words: 2-phenylsulfinylcyclohexanones, configurational isomers, conformational preferences, DFT calculations, exo-anomeric effect.

Derivatives of 2,3-benzo-1-azabicyclo[2•2•1]hept-2-ene

1969 ◽  
Vol 47 (19) ◽  
pp. 3647-3654 ◽  
Author(s):  
Stewart McLean ◽  
A. L. Fallas ◽  
U. O. Trotz ◽  
W. F. Reynolds
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Physical Properties ◽  
Tertiary Amine ◽  
Chemical Properties ◽  
Lone Pair ◽  
Indole Ring ◽  
Nuclear Magnetic Resonance Spectra ◽  
Lone Pair Electrons ◽  
Derivatives Of

2,3-Benzo-1-azabicyclo[2•2•1]hept-2-ene derivatives have been prepared by the introduction of a two-carbon bridge between positions-1 and -3 of the indole ring in 2,3-dimethylindole and tetrahydrocarbazole. In the former case both C-7 epimers were isolated and identified, and their nuclear magnetic resonance spectra were analyzed in detail. In the tetrahydrocarbazole series only one product was obtained and some ambiguity remains concerning the stereochemistry of this material. The physical properties of these compounds are of interest because the lone pair electrons on nitrogen are not able to overlap with the aromatic π system; the chemical properties are characterized by a facile cleavage of the tertiary amine under acylating conditions.

Synthesis and Structural Investigation of Some Electron-Rich Nitroaromatics

2019 ◽  
Vol 72 (4) ◽  
pp. 311
Author(s):  
Jonathan M. White ◽  
Colin E. Skene ◽  
John Deadman ◽  
Ruwan Epa ◽  
Sarah Foenander ◽  
...  
Keyword(s):  
Nitro Group ◽  
Bond Distance ◽  
Lone Pair ◽  
Crystal Structure Analysis ◽  
Nucleophilic Aromatic Substitution ◽  
Anomeric Effect ◽  
Aromatic Substitution ◽  
Nitrogen Lone Pair ◽  
Lone Pair Electrons ◽  
Electron Donation

2,4-Difluoro-, 2,4,6-trifluoro-, and 2,3,4,6,tetrafluoronitrobenzenes undergo nucleophilic aromatic substitution, once, twice, and three times with a variety of amine substituents with a high degree of regiochemical control to provide a range of electron-rich nitrobenzene derivatives. In these structures the nitro group proves a useful structural probe to reveal the varying extents of electron donation from the varying number of amino substituents onto the nitro group as revealed by accurate low temperature X-ray crystal structure analysis, thus increasing electron donation manifests in a decrease in the Ar–NO2 distance consistent with increased double bond character, while the N–O bond distance increases as the oxygens accept the electron density. The effect of delocalization of the aniline nitrogen lone pair onto the nitro group impacts on the geometry and hybridization of the nitrogen substituent and also impacts on the ability of the nitrogen lone pair electrons to participate in other competing electronic interactions, such as the nN–σ*C–S anomeric effect as demonstrated by the thiazolidine substituted derivatives 3c, 4c, and 6c.

scholarly journals Bond-length distributions for ions bonded to oxygen: results for the non-metals and discussion of lone-pair stereoactivity and the polymerization of PO4

2018 ◽  
Vol 74 (1) ◽  
pp. 79-96 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Metal Ions ◽  
Bond Length ◽  
Oxidation State ◽  
Lone Pair ◽  
Bond Valence ◽  
Group 14 ◽  
Coordination Polyhedra ◽  
Bond Lengths ◽  
Secondary Bonds ◽  
Lone Pair Electrons

Bond-length distributions are examined for three configurations of the H+ ion, 16 configurations of the group 14–16 non-metal ions and seven configurations of the group 17 ions bonded to oxygen, for 223 coordination polyhedra and 452 bond distances for the H+ ion, 5957 coordination polyhedra and 22 784 bond distances for the group 14–16 non-metal ions, and 248 coordination polyhedra and 1394 bond distances for the group 17 non-metal ions. H...O and O—H + H...O distances correlate with O...O distance (R 2 = 0.94 and 0.96): H...O = 1.273 × O...O – 1.717 Å; O—H + H...O = 1.068 × O...O – 0.170 Å. These equations may be used to locate the hydrogen atom more accurately in a structure refined by X-ray diffraction. For non-metal elements that occur with lone-pair electrons, the most observed state between the n versus n+2 oxidation state is that of highest oxidation state for period 3 cations, and lowest oxidation state for period 4 and 5 cations when bonded to O2−. Observed O—X—O bond angles indicate that the period 3 non-metal ions P3+, S4+, Cl3+ and Cl5+ are lone-pair seteroactive when bonded to O2−, even though they do not form secondary bonds. There is no strong correlation between the degree of lone-pair stereoactivity and coordination number when including secondary bonds. There is no correlation between lone-pair stereoactivity and bond-valence sum at the central cation. In synthetic compounds, PO4 polymerizes via one or two bridging oxygen atoms, but not by three. Partitioning our PO4 dataset shows that multi-modality in the distribution of bond lengths is caused by the different bond-valence constraints that arise for Obr = 0, 1 and 2. For strongly bonded cations, i.e. oxyanions, the most probable cause of mean bond length variation is the effect of structure type, i.e. stress induced by the inability of a structure to follow its a priori bond lengths. For ions with stereoactive lone-pair electrons, the most probable cause of variation is bond-length distortion.

Lone pair interactions in dimethoxymethane and anomeric effect

1979 ◽  
Vol 57 (4) ◽  
pp. 424-435 ◽  
Author(s):  
Igor Tvaroška ◽  
Tomaš Bleha
Keyword(s):  
Lone Pair ◽  
Theoretical Interpretation ◽  
Orbital Interaction ◽  
Anomeric Effect ◽  
Gauche Conformation ◽  
Orbital Interactions ◽  
Dipole Interactions ◽  
Lone Pairs ◽  
Molecular Orbital Analysis ◽  
P Type

Perturbation molecular orbital analysis has been used for a computation of the through-bond and through-space orbital interactions of oxygen lone pairs in dimethoxymethane (DMM). The analysis predicts the symmetrical combination of p-type lone pairs as a highest occupied orbital in an antiperiplanar conformation. The conformational dependence of through-bond orbital interactions has the character of the V2 term in the Fourier expansion of the rotation potential function about the C—O bond. Contrary to the recent theoretical interpretation that the anomeric effect (preference of gauche conformation) is caused by superjacent orbital control, the orbital interactions in DMM are not dominant terms with respect to the anomeric or exoanomeric effect. The dipole–dipole interactions of the C—O bonds stabilizing the gauche conformation should thus be considered as the primary cause of the anomeric effect in DMM. The frontier orbital energies and geometric parameters in DMM are strongly influenced by a variation of orbital interaction with rotation. Results obtained for DMM are used to explain the conformational behaviour of other molecules containing the acetal moiety, such as pyrane heterocycles, sugars, and polyoxymethylene.

Bond-length distributions for ions bonded to oxygen: Metalloids and post-transition metals

2017 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Ions ◽  
Bond Length ◽  
Lone Pair ◽  
Transition Metal Ions ◽  
Oxygen Lone Pair

Bond-length distributions are examined for thirty-three configurations of the metalloid ions and fifty-six configurations of the post-transition-metal ions bonded to oxygen. Lone-pair stereoactivity is discussed.

Bond-length distributions for ions bonded to oxygen: Metalloids and post-transition metals

2017 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Transition Metal ◽  
Transition Metals ◽  
Metal Ions ◽  
Bond Length ◽  
Lone Pair ◽  
Transition Metal Ions ◽  
Oxygen Lone Pair

Bond-length distributions are examined for thirty-three configurations of the metalloid ions and fifty-six configurations of the post-transition-metal ions bonded to oxygen. Lone-pair stereoactivity is discussed.

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