Nuclear magnetic resonance and the conformation of some derivatives of Michler's ketone

¹H NMR spectra are reported for Michler's ketone and twenty of its derivatives, along with ¹³C chemical shifts for five of the compounds. ¹H chemical shifts show only small changes with increasing substitution at the sterically hindered 2-position. Estimates of the dihedral angle between the benzene ring and C? CO? C planes have been obtained from the chemical shifts of C?O and 4-C for ketones 1, 3, 5, 15 and 16 . These angles are both internally consistent and very similar to dihedral angles determined by other methods for corresponding compounds in the benzophenone series.     

1H NMR lanthanide-induced Shift investigations of highly flexible molecules III: Applications to alcohols,aldehydes, esters,and amines

Summary Two new methods (RANDOM-LIS and STEED-LIS) with random selection of up to ten dihedral angles were applied for the determination of preferred conformers of flexible molecules (alcohols, aldehydes, esters, and amines, respectively, with only one coordination site) by LIS studies. The results proved to be useful. The preferred complexation conformation was detected only in cases where conformational changes of the substrate took place to improve complexation to the LIS reagent. Force field calculations (RANDOM-PIMM) and Simple Hard Sphere Model calculations (RANDOM-SHSM and STEED-SHSM), using the same algorithm of randomly varying the dihedral angles, support the results obtained.For parts I and II, see Refs. [1] and [2]     

Topological steric effect index and its application

This paper proposed a Topological Steric Effect Index (TSEI) of a group based on the relative specific volume of the reaction center screened by the atoms of the substituents. Investigated results show good correlations between the parameter TSEI and the dihedral angles between both phenyl rings determined by photoelectron spectroscopy for 7 alkylbiphenyl compounds and calculated by a molecular mechanics force field for 78 alkylbiphenyl compounds, whose correlation coefficients are 0.9912 and 0.9845, respectively. The TSEI value of the group is easily calculated and has a clear physical meaning. In addition, it is correlated well to dihedral angles of the 1,2-disubstituted benzene compounds, stereoselectivity of organomagnesium compounds addition to some cyclohexanones and cyclopentanones, and the relative rates of some SN2 reactions.     

Dihedral‐Angle‐Controlled Crossover from Static Hole Delocalization to Dynamic Hopping in Biaryl Cation Radicals

In cases of coherent charge‐transfer mechanism in biaryl compounds the rates follow a squared cosine trend with varying dihedral angle. Herein we demonstrate using a series of biaryl cation radicals with varying dihedral angles that the hole stabilization shows two different regimes where the mechanism of the hole stabilization switches over from (static) delocalization over both aryl rings to (dynamic) hopping. The experimental data and DFT calculations of biaryls with different dihedral angles unequivocally support that a crossover from delocalization to hopping occurs at a unique dihedral angle where the electronic coupling (H _ab) is one half of reorganization (λ ), that is, H _ab=λ /2. The implication of this finding in non‐coherent charge‐transfer rates is being investigated.     

Conformational evaluation and detailed 1H and 13C NMR assignments of eremophilanolides

Extensive application of 1D and 2D NMR methodology, combined with molecular modeling, allowed the complete 1H and 13C NMR assignments of eremophilanolides from Senecio toluccanus. Comparison of the experimental 1H, 1H coupling constant values with those generated employing a generalized Karplus-type relationship, using dihedral angles extracted from MMX and DFT calculations, revealed that the epoxidized eremophilanolides 1 and 2 show conformational rigidity at room temperature, whereas molecules 3-6, containing an isolated double bond, are conformationally mobile.     

CONFORMATIONAL INVESTIGATION OF SOME SYMMETRICALLY SUBSTITUTED DIALKYL MONO-SULFIDES AND DISULFIDES BY IR SPECTROSCOPY

Abstract

Several infrared and Raman studies have been performed on compounds containing the disulfide group in the region of C-S and S-S stretching modes (1–4) in order to get a better insight of the correlations between molecular conformation and peculiar geometry parameters of the dihedral angle CS-SC.     

Synthesis and liquid crystalline properties of novel compounds containing a 3-fluoro-4-cyanophenoxy group

A series of novel compounds containing a 3-fluoro-4-cyanophenoxy group were synthesized and fully characterized by IR and ¹H NMR, and their mesomorphic properties were studied. Seven compounds exhibited enantiotropic nematic phases and three compounds exhibited monotropic nematic phases, as confirmed by differential scanning calorimetry and polarizing optical microscopy. Selected properties of the liquid crystalline compounds synthesized were calculated by ab initio methods at a HF/6-31G level. The bond lengths, bond angles and dihedral angles of the fragments with the same structure change little between the compounds. All the compounds with a terminal alkoxy chain approached a planar structure.     

银桥联六苯基苯配合物的结构与导电性

在一定研究基础上合成出分子式为{Ag~2(hpb)(ClO~4)~2[(CH~3)~2CO]~2}1(hpb=C~6Ph~6)的二核银配合物,并制备出自由配体hpb的单晶2,其结构由X射线单晶衍射表征。将这两种化合物与先前研究结果比较发现,配合物的分子空间结构不仅依赖于阴离子大小、溶剂性质,还取决于溶剂类型和自由配体的分子空间结构与排列,并且这种结构变化导致了导电性的不同。     

THE PHOSPHAZENES–STRUCTURAL PARAMETERS AND THEIR RELATIONSHIPS TO PHYSICAL AND CHEMICAL PROPERTIES

Abstract

A systematic study of crystallographic data has revealed a number of correlations between structural parameters, (e.g., bond angles, bond lengths, dihedral angles) and physical and chemical properties in phosphazenes and related compounds. These include (a) endocyclic bond angles NPN and PNP and their relationships to group electronegativities; (b) endocyclic bond angles NPN and PNP in geminal cyclotriphosphazatrienes, N₃P₃RR′X₄ (X = F, Cl) and their relationships to basicity; (c) deviations from some relationships due to ring puckering and the use of mathematical techniques to “flatten out” these rings; (d) ³⁵Cl nuclear quadrupole resonance frequencies and P–Cl bond lengths and other relationships; (e) exocyclic bond angles viz. OPO, NPN, ClPCl, CPC etc. versus ³¹P NMR chemical shifts; (f) ring compression and deformation and unusual mass spectrometric and bulk polymerisation properties; (g) relationships in phosphazenylcyclophosphazenes between crystal structure, ⁴ J(PP) coupling constants, basicity and conformation; (h) relationships between spin-spin coupling constants, dihedral angles in, and conformations of, spiroderivatives of cyclophosphazenes–trigonal planar versus pyramidal nitrogen atoms.     

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X)

The (2,3)J(CH) dependence on dihedral angle (theta H--C--C--X) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained (2,3)J(CH) values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of (3)J(CH) and the dihedral angle between the hydrogen and the coupled carbon (R2 = 0.88).     

Conformations of cyclobutane

The literature concerning the structures of compounds containing saturated, 4-carbon rings is reviewed critically, and the variety of conformations (dihedral angles of 0° to 30° ± 6°) of the cyclobutane ring are tabulated and discussed.     

Synthesis and liquid crystalline properties of novel compounds containing a 3‐fluoro‐4‐cyanophenoxy group

A series of novel compounds containing a 3‐fluoro‐4‐cyanophenoxy group were synthesized and fully characterized by IR and ¹H NMR, and their mesomorphic properties were studied. Seven compounds exhibited enantiotropic nematic phases and three compounds exhibited monotropic nematic phases, as confirmed by differential scanning calorimetry and polarizing optical microscopy. Selected properties of the liquid crystalline compounds synthesized were calculated by ab initio methods at a HF/6‐31G level. The bond lengths, bond angles and dihedral angles of the fragments with the same structure change little between the compounds. All the compounds with a terminal alkoxy chain approached a planar structure.     

Structures and conformations of trifluoromethanesulfonic anhydride, (CF3SO2)2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF3SO2)2CF2

The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF₃SO₂)₂CF₂ have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C₂ symmetry and one with C₁ symmetry. In both compounds structures with C₂ symmetry and dihedral angles SOSC ≈ 100° ((CF₃SO₂)₂O) and SCSC ≈ 150° ((CF₃SO₂)₂CF₂) are lowest in energy. According to the GED analyses the dominant conformer of (CF₃SO₂)₂O possesses C₂ symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF₃SO₂)₂CF₂ only one conformer with C₂ symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given.     

From tropos to atropos: 5,5′-bridged 2,2′-bis(diphenylphosphino)biphenyls as chiral ligands for highly enantioselective palladium-catalyzed hydrogenation of α-phthalimide ketones

A class of atropisomeric diphosphine ligands with a wide range of dihedral angles has been developed. X-ray study of the Pd(II) complexes of these ligands showed that as the bridge length increased, the dihedral angles and the ligand bite angles increased as well, while an excessive increase in bridge length had a reverse effect. It was found that there was a correlation between the ligand dihedral angles and the enantioselectivity in Pd-catalyzed asymmetric hydrogenation of α-phthalimide ketones, and excellent enantioselectivities of up to 99% ee were afforded.     

Structures and conformations of trifluoromethanesulfonic anhydride, (CF3SO2)2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF3SO2)2CF2

The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF₃SO₂)₂CF₂ have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C₂ symmetry and one with C₁ symmetry. In both compounds structures with C₂ symmetry and dihedral angles SOSC ≈ 100° ((CF₃SO₂)₂O) and SCSC≈ 150° ((CF₃SO₂)₂CF₂ are lowest in energy. According to the GED analyses the dominant conformer of (CF₃SO₂)₂O₂ possesses C₂ symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF₃SO₂)₂CF₂ only one conformer with C₂ symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given.     

Half-chair conformations of unsaturated heterocyclic compounds

The vicinal proton coupling constants were obtained for some 6-membered ring unsaturated heterocyclic compounds. The R values and ring dihedral angles were determined and found to be consistent with half-chair conformations. Relative to saturated heterocyclic compounds, the effect of the sulfur atom on ring puckering was attenuated. However, an increase in ring puckering resulted from the sulfone group and was attributed to torsional energy.     

Dihedral Angles in Cyclic Molecules

The experimental and quantum-chemical values of dihedral angles are analyzed for mono- and bicyclic molecules. Correlations have been found for the bond and dihedral angles.     

Etude de la conformation des n-aryl azoles par la methode e.h.t. (extended hückel theory)

E.H.T. calculations of total energy as a function of dihedral angle are presented for 8 N-aryl azoles, six with dihedral angle α and two with dihedral angles α and β. The rotational barriers to the planar and to the orthogonal geometries are discussed. The dihedral angles α or β corresponding to the minimum of the calculated potential curve or surface are important; a uniform correction of these values is necessary to find the experimental values.     

Realistic sampling of amino acid geometries for a multipolar polarizable force field

The Quantum Chemical Topological Force Field (QCTFF) uses the machine learning method kriging to map atomic multipole moments to the coordinates of all atoms in the molecular system. It is important that kriging operates on relevant and realistic training sets of molecular geometries. Therefore, we sampled single amino acid geometries directly from protein crystal structures stored in the Protein Databank (PDB). This sampling enhances the conformational realism (in terms of dihedral angles) of the training geometries. However, these geometries can be fraught with inaccurate bond lengths and valence angles due to artefacts of the refinement process of the X‐ray diffraction patterns, combined with experimentally invisible hydrogen atoms. This is why we developed a hybrid PDB/nonstationary normal modes (NM) sampling approach called PDB/NM. This method is superior over standard NM sampling, which captures only geometries optimized from the stationary points of single amino acids in the gas phase. Indeed, PDB/NM combines the sampling of relevant dihedral angles with chemically correct local geometries. Geometries sampled using PDB/NM were used to build kriging models for alanine and lysine, and their prediction accuracy was compared to models built from geometries sampled from three other sampling approaches. Bond length variation, as opposed to variation in dihedral angles, puts pressure on prediction accuracy, potentially lowering it. Hence, the larger coverage of dihedral angles of the PDB/NM method does not deteriorate the predictive accuracy of kriging models, compared to the NM sampling around local energetic minima used so far in the development of QCTFF. © 2015 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

Dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans. Part II: Assignment of (1)H and (13)C NMR spectra

The (1)H and (13)C NMR spectra of dicondensed indolinobenzospiropyrans as precursors of thermo- and photochromic spiropyrans, DC1-DC5, were completely assigned. Especially, the (1)H assignment and coupling characteristics of the diastereotopic protons at the carbon-3 position of the benzopyran rings were achieved by conducting (1)H-(1)H COSY and nOe experiments. The dihedral angles (theta(1), theta(2) and theta(3)) calculated from the experimental values of the vicinal coupling constants ((3)J) of DC5 are in good agreement with the observed values in the solid state. All of the carbons in the DC dye molecules were investigated through a combination of heteronuclear 2D-shift correlation spectroscopy (HETCOR) and DEPT135.