Adjacent Phenyl Groups Research Articles

Predictive elucidation of conformational characteristics and configurational properties of poly(1-methylphosphirane) and poly(1-phenylphosphirane) as a molecular design

Conformational characteristics and configurational properties of poly(1-methylphosphirane) (PMePP) and poly(1-phenylphosphirane) (PPhPP) have been predictively elucidated by the refined rotational isomeric state scheme coupled with ab initio molecular orbital and density functional calculations. The lone pair of the phosphorus atom adopts an sp hybrid orbital. Owing to the high s character (50%), the polyphosphiranes exhibit low proton (hydrogen) affinities, and hence the lone pair does not form any intramolecular attractive interactions with hydrogen. As the meso-diad probability varies from 0 (syndiotactic) to 1 (isotactic), the characteristic ratio of PMePP slightly increases from 6.7 to 7.4, whereas that of PPhPP considerably decreases from 38 to 7.3. The large dimension of syndiotactic PPhPP is chiefly due to π-π attractions formed between adjacent phenyl groups. The trivalent phosphorus atom may be bonded to heavy, noble, and transition metals but readily or gradually oxidized. The usefulness and necessity of the polyphosphiranes have been assessed.

Metalated Nitriles: Internal 1,2-Asymmetric Induction

Alkylations of conformationally constrained acyclic nitriles containing vicinal dimethyl groups and an adjacent phenyl group or trisubstituted alkene are exceptionally diastereoselective. Probing the alkylation stereoselectivity with a series of C- and N-metalated nitriles implicates a reactive conformation in which an sp2-hybridized substituent projects over the metalated nitrile to avoid allylic strain. Steric screening thereby directs the electrophilic attack to the face of the metalated nitrile opposite the projecting substituent. Excellent stereoselectively is maintained in a diverse range of alkylations that efficiently install quaternary centers, even with isopropyliodide in which a contiguous array of tertiary-quaternary-tertiary stereocenters is created! Screening the conformational requirements with a series of acyclic nitriles and esters reveals the key structural requirements for high selectivity while providing a robust, predictive model that accounts for comparable ester alkylations affording the opposite diastereomer! The intensive survey of metalated nitrile alkylations identifies the key structural features required for high 1,2-asymmetric induction, addresses the long-standing challenge of asymmetric alkylations with acylic metalated nitriles, and provides a versatile method for installing hindered quaternary centers with excellent stereocontrol.

1-Hydroxy-1,1,3,3,3-pentaphenyldisiloxane, [Si2O(OH)(Ph)5], at 150 K

In the crystal structure of the title compound, C30H26O2Si2, one Si(Ph)3 residue is bound to another Si(OH)(Ph)2 residue via a nonlinear Si—O—Si bridge. The asymmetric unit is composed of four [Si2O(OH)(Ph)5] molecules. Each pair of adjacent molecules inter­acts via strong and highly directional O—H⋯O hydrogen bonds connecting neighbouring Si—OH units, and via inter-unit O—H⋯π contacts connecting the second hydroxyl groups with adjacent phenyl groups.

1-Hydroxy-1,1,3,3,3-pentaphenyldisiloxane, [Si2O(OH)(Ph)5], at 100 K

In the crystal structure of the title compound, C30H26O2Si2, one Si(Ph)3 residue is bound to another Si(OH)(Ph)2 residue via a non-linear Si—O—Si bridge. The asymmetric unit is composed of two such molecules which inter­act, on the one hand, via a strong and highly directional O—H⋯O hydrogen bond involving the two neighbouring Si—OH units and, on the other, via an O—H⋯π contact connecting the second hydroxyl group with an adjacent phenyl group.

Metalated Nitriles: Internal 1,2‐Asymmetric Induction

Alkylations of conformationally constrained acyclic nitriles containing vicinal dimethyl groups and an adjacent phenyl group or trisubstituted alkene are exceptionally diastereoselective. Probing the alkylation stereoselectivity with a series of C- and N-metalated nitriles implicates a reactive conformation in which an sp2-hybridized substituent projects over the metalated nitrile to avoid allylic strain. Steric screening thereby directs the electrophilic attack to the face of the metalated nitrile opposite the projecting substituent. Excellent stereoselectively is maintained in a diverse range of alkylations that efficiently install quaternary centers, even with isopropyliodide in which a contiguous array of tertiary−quaternary−tertiary stereocenters is created! Screening the conformational requirements with a series of acyclic nitriles and esters reveals the key structural requirements for high selectivity while providing a robust, predictive model that accounts for comparable ester alkylations affordin...

Hydrogen–Hydrogen Bonding in Planar Biphenyl, Predicted by Atoms‐In‐Molecules Theory, Does Not Exist

Based on an Atoms-in-Molecules (AIM) analysis, Matta et al. recently claimed evidence for the existence of hydrogen-hydrogen bonding between ortho-hydrogen atoms, pointing towards each other from adjacent phenyl groups in planar biphenyl. This AIM result is opposed to the classical view that nonbonded steric repulsion between the ortho-hydrogen atoms is responsible for the higher energy of the planar as compared to the twisted geometry of biphenyl. In the present work, we address the question if hydrogen-hydrogen bonding in biphenyl exists, as suggested by AIM, or not. To this end, we have analyzed the potential energy surface for internal rotation of biphenyl in terms of two interacting phenyl radicals using density functional theory (DFT) at BP86/TZ2P. A detailed analysis of the bonding mechanism and a quantitative bond energy decomposition in the framework of Kohn-Sham DFT show that Pauli (or overlap) repulsion, mainly between C(ortho)--H(ortho) phenyl MOs, prevents biphenyl from being planar and forces it to adopt a twisted equilibrium geometry. Furthermore, a derivative of biphenyl in which all four ortho-hydrogen atoms have been removed does adopt a planar equilibrium geometry. Thus, our results confirm the classical view of steric repulsion between ortho-hydrogen atoms in biphenyl and they falsify the hypothesis of hydrogen-hydrogen bonding.

Controlling the regiochemistry of radical cyclizations

This review describes the results of our recent studies on the control of the regiochemistry of radical cyclizations. N-vinylic alpha-chloroacetamides generally cyclized in a 5-endo-trig manner to give five-membered lactams, whereas 4-exo-trig cyclization occurred when the cyclized radical intermediates were highly stabilized by an adjacent phenyl or phenylthio group to afford beta-lactams. The 5-exo or 6-exo cyclization of aryl radicals onto the alkenic bond of enamides could be shifted to the corresponding 6-endo or 7-endo mode of cyclization by a positional change of the carbonyl group of enamides. The 6-endo- and 7-endo-selective aryl radical cyclizations were applied to radical cascades for the synthesis of alkaloids such as phenanthroindolizidine, cephalotaxine skeleton, and lennoxamine. The 5-exo-trig cyclization of an alkyl radical onto the alkenyl bond of enamides could also be shifted to the 6-endo mode by a positional change of the carbonyl group of enamides. The 6-endo- selective cyclization was applied to the radical cascade to afford a cylindricine skeleton. Other examples of controlling the regiochemistry of radical cyclizations and their applications to the synthesis of natural products are also discussed.

Microcalorimetric Study on Micellization of Nonionic Surfactants with a Benzene Ring or Adamantane in Their Hydrophobic Chains

The micellization of a novel family of nonionic surfactants poly(oxyethylene) glycol alkyl ethers has been studied by microcalorimetry. One of the surfactants has adamantane, and the other nonionic surfactants have a benzene ring in their hydrophobic chains, which moves from the terminal of the hydrophobic chain toward the headgroup. Moreover, the alkyl chain of the nonionic surfactants is straight or branched. Both the critical micelle concentration (cmc) and the thermodynamic parameters associated with the micelle formation have been obtained. The cmc decreases and the enthalpy of micelle formation (deltaH(mic)) becomes less positive gradually as the length of hydrophobic chain increases, whereas the values of cmc and deltaH(mic) tend to increase for the surfactants with a longer ethylene oxide chain. However, the deltaH(mic) value of the surfactant with seven carbon atoms in a hydrophobic chain is more positive than that of the surfactant with six carbon atoms in a hydrophobic chain. Comparing with the nonionic surfactant with a methylene hydrophobic chain, the surfactants with benzene rings and adamantane groups have larger cmc values and the cmc values increase with the size of the groups. Furthermore, moving the phenyl group from the terminal of the hydrophobic chain to the neighbor of the hydrophilic headgroup leads to the decreased cmc. Both the variation of hydrophobic interaction from the movement of phenyl group and pi-pi interaction among adjacent phenyl groups affect deltaH(mic) values.

Novel Supramolecular Frameworks Self‐Assembled from a Two‐Dimensional Polymeric Network: Synthesis and Crystal Structure of a Macrocyclic Organotin(IV) Complex

AbstractThe two‐dimensional polymer [nBu2Sn(O2CC6H4)]4 has been synthesized by the self‐assembly of di‐n‐butyltin oxide and 4‐carboxyphenylboronic acid. The X‐ray crystal structure shows that the metal ions display a trigonal bipyramidal coordination geometry to bind the endocyclic oxygen atom. Intermolecular π–π stacking interactions between adjacent phenyl groups of the ligand cause the self‐assembly into a 1D chain. In this chain one oxygen atom of the carboxylate group binds to one [nBu2Sn(O2CC6H4)]4 unit to give rise to a 2D architecture. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Comparative Studies on the Micellization of Sodium Bis(4-phenylbutyl) Sulfosuccinate and Sodium Bis(2-ethylhexyl) Sulfosuccinate and Their Interaction with Hydrophobically Modified Poly(acrylamide)

The micellization process of sodium bis(4-phenylbutyl) sulfosuccinate (SBPBS) has been studied compared to that of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) by surface tension, steady-state fluorescence, microcalorimetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements. Meanwhile, the interaction of these two surfactants with hydrophobically modified poly(acrylamide) (HMPAM) was investigated. The results show that the surface tension at the critical micelle concentration (cmc) of SBPBS and the micropolarity probed by pyrene in SBPBS aggregates are both larger than those of AOT. The enthalpy change of micellization (DeltaH(mic)) of AOT is endothermic, while it is exothermic for SBPBS. Strong pi-pi interaction among the adjacent phenyl groups of SBPBS molecules is likely the cause for the above properties of SBPBS. Moreover, vesicles are observed for AOT and SBPBS by DLS and TEM, especially for AOT, whose micelle-vesicle transition has been first confirmed by its calorimetric curve. In the surfactant-HMPAM systems, the critical aggregation concentration (cac), the saturation concentration of aggregation (C(2)), and the thermodynamic parameters of binding have also been determined. The conclusion may be drawn that the binding strength of SBPBS onto HMPAM is stronger than that of AOT.

2,2-Bis(chloromethyl)propylene]bis(diphenylstibine)

The title compound, [Sb2(C6H5)4(C5H8Cl2)], is the product of a substitution reaction of 2,2-bis­(chloro­methyl)-1,3-di­chloro­propane with sodium di­phenyl­stibide. Adjacent phenyl groups embrace each other in a parallel fashion in order to minimize interaction. The mol­ecule has crystallographic twofold rotation symmetry.

A Three-Dimensionally Oriented Texture for Poly(α,α,α‘,α‘-tetrafluoro-p-xylylene)

Films of poly(α,α,α‘,α‘-tetrafluoro-p-xylylene) prepared by vapor deposition polymerization are highly crystalline and have uniplanar orientation. This orientation is maintained on drawing ×10 at 350 °C, when the chains become aligned parallel to the direction of draw, leading to a texture of three-dimensionally oriented crystals. Thirty-five X-ray reflections are resolved by controlled rotation and tilting of the drawn specimen, and these can be indexed by a triclinic unit cell with dimensions a = 5.36 A, b = 5.92 A, c = 6.57 A (chain axis repeat), α = 97.0°, β = 63.1°, and γ = 73.1°, containing one monomer unit. Molecular mechanics favors a trans-planar conformation for the −CF2−CF2 linkage which is inclined at 90° to the adjacent phenyl groups, leading to a fiber repeat that is equal to that observed. Packing analyses point to a structure in which the phenyl groups are approximately perpendicular to the ac plane, and this gives good agreement between the observed and calculated structure amplitudes (R ...

Deprotonation-Induced Enantioselective Aggregation and Deprotonation-Induced Ligand Rearrangement of Copper(II) Complexes Yield 1D Homochiral and Heterochiral Chains and a Cyclic Tetramer, Respectively.

The copper(II) complexes of protonated pentadentate Schiff-base ligands with [Cu(H(2)L(n))](ClO(4))(2) formula (n = 3-6, 3-6) have been synthesized and characterized (H(2)L(3) = N-((2-methylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-methylimidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(4) = N-((2-phenylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2-phenyl-imidazol-4-yl)methylene)-4'-aminobutylamine, H(2)L(5) = N,N'-bis((2-phenylimidazol-4-yl)methylene)-3,3'-diaminodipropylmethylamine, H(2)L(6) = N-((2-methylimidazol-4-yl)methylene)-2-aminoethyl-N'-((2-methylimidazol-4-yl)methylene)-3'-aminopropylamine. The mono-deprotonated complexes 3', 4', and 5' contain one imidazole and one imidazolate groups per unit and are Delta (clockwise) or Lambda (anticlockwise) enantiomorphs due to the spiral arrangement of the ligand around copper(II) ion. They function as chiral building components for a self-assembly process resulting from the formation of hydrogen bonds between the imidazole and imidazolate groups of adjacent units to yield 1D zigzag-chain structures. The distance between hydrogen-bonded nitrogen atoms is 2.81(2), 2.832(9), and 2.875(9) Å for 3', 4', and 5', respectively. The crystal lattice of 3' yielded either.DeltaDeltaDelta. or.LambdaLambdaLambda. isotactic 1D zigzag-chains, while the crystal lattices of 4' and 5' yielded.DeltaLambdaDeltaLambda. syndiotactic 1D zigzag-chains. In 3', two adjacent methyl groups at the 2-position connected by hydrogen bond array in the same direction, thus allowing homochiral aggregation of the complex molecules in a 1D chain. On the other hand, in 4' and 5', two adjacent bulky phenyl groups require opposite orientations, thus allowing heterochiral aggregation. Enantioselective aggregation with homochirality or heterochirality can thus be controlled with suitable substituents. While its mononuclear precursor 6 is pentacoordinated with the N(5) donor set of the pentadentate ligand H(2)L(6), the deprotonated complex 6' has an imidazolate-bridged tetranuclear cyclic structure with a Cu-Cu distance of 6.086(2) Å. The ligand in 6' is tetradentate and includes an hexahydropyrimidine ring resulting from a deprotonation induced rearrangement reaction.

First Synthesis of Exomethylene Paracyclophanes and Their Structural Properties

A series of novel exomethylene paracyclophanes was synthesized by the intramolecular benzannulation of conjugated enynes in the presence of tetrakis(triphenylphosphine)palladium(0). Detailed spectral studies revealed that the conformation of the exomethylene paracyclophanes depends on the size of the ring; the alkene moiety does not conjugate with the adjacent phenyl group in the smaller exomethylene paracyclophanes.

Spontaneous oxidation of C60Ph5X (X = H, Cl) to a benzo[b]furanyl[60]fullerene

A. G. Avent, P. R. Birkett, A. D. Darwish, H. W. Kroto, R. Taylor and D. R. M. Walton, Chem. Commun., 1997, 1579 DOI: 10.1039/A703803H

Formation of C 70Ph 10 and C 70Ph 8 from the electrophile C 70Cl 10

In the presence of ferric chloride, benzene readily undergoes electrophilic substitution by C 70Cl 10 to give both yellow C 70Ph 10 and orange-red C 70Ph 8, each of which is luminescent. Their structures have been characterised by 1H and 13C NMR spectroscopy [including nOe and two-dimensional (COSY) analysis], and by UV, IR, and mass spectrometry. C 70Ph 10 is not formed directly from C 70Cl 10, but rather by further phenylation of the intermediate C 70Ph 8. The adjacent phenyl groups of C 70Ph 10 are sterically prevented from rotating at room temperature.

Competitive Inhibition of HIV-1 Protease by Biphenyl Carboxylic Acids

A novel series of nonpeptidic compounds that contain a biphenyl carboxylic acid group have been shown to inhibit HIV-1 protease. The active compounds, most of which are highly soluble, have IC50 values in the range of 3.4-74 μM. The structure-inhibitory activity relationship demonstrates the necessity of the biphenyl carboxylic acid group for inhibition, which is enhanced by the presence of a sulfone group and by halogenation of an adjacent phenyl group. A double reciprocal plot of inhibition data on two of the compounds clearly shows that the inhibition occurs in a competitive manner, with Ki values of 1.1 and 3.4 μM. Inhibition by several of the compounds was found to be reversible and fast-binding, while one of the biphenyl carboxylic acids inhibits in a reversible slow-binding manner. Time-dependent inhibition studies were conducted on this compound, and it was determined to have the kinetic values of kon = 0.18 μM−1min−1, koff = 9.7 × 10−2min−1, and Ki = 0.14 μM. Thus, the slow-binding inhibitor is the most potent in the series. Molecular modeling has provided information on a possible binding mode for two different biphenyl carboxylic acid inhibitors of HIV-1 protease.

On the stabilization of carbanions by adjacent phenyl, cyano, methoxy-carbonyl, and nitro groups in the gas phase

By using the method of Fourier transform ion cyclotron resonance mass spectrometry, substituent stabilization energies of homologous series of cycloalkyl carbanions, X- c-C nH 2n−2 − (n = 3,4,5,6,7) with π-accepting substituents (X = Ph, CN, COOMe, NO 2) have been determined experimentally in the gas phase as the difference between the proton affinity of the substituted and corresponding unsubstituted (X = H) cycloalkyl carbanions. The stabilization energy data have been analyzed in terms of Taft's parametrization of polarizability, field/inductive, and resonance effects. The linear regression analyses show excellent correlations within the XCH − 2, X- c-C nH 2n−2 − (n = 4,5,6,7), and X- c-C 3H − 4 carbanion series, from which it appears that the contributions of polarizability effects are independent of the above type of carbanions and only depend on the nature of the substitutuent. Further, it follows that inductive stabilization is more effective in the substituted methyl, XCH − 2, than in the substituted cycloalkyl, X- c-C nH 2n−2 − (n = 4,5,6,7) carbanions. This result suggests that inductive stabilization is counteracted by the electron releasing effect of alkyl groups. Resonance stabilization is significantly more effective in the substituted cycloalkyl, X- c-C nH 2n−2 − (n = 4,5,6,7), than in the substituted methyl, XCH 2 −, carbanions, which suggests that in contrast to inductive stabilization, resonance stabilization is assisted by the electron releasing effect of alkyl groups. Finally, it appears that substituent stabilization in the geometrically restricted substituted cyclopropyl carbanions, X- c-C 3H 4 −, is dramatically less effective than in the corresponding geometrically unrestricted larger substituted cycloalkyl carbanions, X- c-C nH 2n−2 − (n = 4,5,6,7). The linear regression analyses of the substituted cycloalkyl carbanions indicate that reduction of the stabilization energy is caused not exclusively by a geometrically hindered resonance stabilization, but also to a smaller extent by a less efficient inductive stabilization in the substituted cyclopropyl carbanions.

Structure of 5,5',6,6'-tetraphenyl-3,3'-bi-1,2,4-triazine

The title compound (BDT) crystallizes in an s-trans conformation, the inversion center lying on the bond between the two triazine rings. The triazine rings are coplanar with the phenyl rings twisted 26.5 and 54.2 o relative to them. Steric crowding caused by the adjacent phenyl groups is reflected in a distortion (±5 o ) of the exocyclic bond angles. The heteroaromatic rings deviate significantly from planatarity; 0.046 (3) A being the maximum deviation from the least-quares plane. The observed molecular dimensions are in good agreement with published structures of 1,2,4-triazines

Macromolecule-Metal Complexes for Gas Separation

Abstract Macromolecule-copper(I) chloride complexes have been prepared for the separation of carbon monoxide and ethylene from gas mixtures with hydrogen, nitrogen, carbon dioxide, methane, and water. A toluene solution of a polystyrene-aluminum copper(I) chloride complex can separate carbon monoxide selectively and retains this function even on contact with gas containing water. Strong charge-transfer absorption bands have been found in the 380-500 nm region for the toluene solution of polystyrene-aluminum copper(I) chloride complex. A solution of 1, 3-diphenylpropane-aluminum copper(I) chloride complex also exhibits similar absorption bands. A continuous variation plot using the chemical shift change in 13C-NMR shows a 1:1 interaction between 1,3-diphenylpropane and aluminum copper(I) chloride. These results suggest a two-way interaction between the adjacent phenyl groups of polystyrene and aluminum copper(I) chloride. A resin bead of crosslinked polystyrene-aluminum copper(I) chloride complex has been ...