Benzene Substituents Research Articles

Determination of Photoionization Cross-Sections of Different Organic Molecules Using Gas Chromatography Coupled to Single-Photon Ionization (SPI) Time-of-Flight Mass Spectrometry (TOF-MS) with an Electron-Beam-Pumped Rare Gas Excimer Light Source (EBEL): Influence of Molecular Structure and Analytical Implications

This work describes a fast and reliable method for determination of photoionization cross-sections (PICS) by means of gas chromatography (GC) coupled to single-photon ionization mass spectrometry (SPI-MS). Photoionization efficiency (PIE) data for 69 substances was obtained at a photon energy of 9.8 ± 0.4 eV using an innovative electron-beam-pumped rare gas excimer light source (EBEL) filled with argon. The investigated analytes comprise 12 alkylbenzenes as well as 11 other substituted benzenes, 23 n-alkanes, ten polyaromatic hydrocarbons, seven aromatic heterocycles, and six polyaromatic heterocycles. Absolute PICS for each substance at 9.8 eV are calculated from the relative photoionization efficiencies of the compounds with respect to benzene, whose photoionization cross-section data is well known. Furthermore, a direct correlation between the type of benzene substituents and their absolute PICS is presented and discussed in depth. Finally, comparison of previously measured photoionization cross-sections for 20 substances shows good agreement with the data of the present work.

{4-Hydroxy-N′-[(2E,3Z)-4-oxido-4-phenylbut-3-en-2-ylidene]benzohydrazidato}diphenyltin(IV) methanol monosolvate

Two independent diphenyl­tin mol­ecules and two independent methanol mol­ecules comprise the asymmetric unit of the title compound, [Sn(C6H5)2(C17H14N2O3)]·CH3OH. The Sn atom in each is five-coordinated by a tridentate ligand and the ipso-C atoms of the Sn-bound benzene substituents. The resulting C2N2O donor set defines a coordination geometry that is inter­mediate between trigonal-bipyramidal (TP) and square-pyramidal (SP), with one mol­ecule slightly tending towards TP and the other slightly towards SP. The mol­ecules differ in terms of the relative orientations of the terminal benzene rings [dihedral angles = 45.71 (18) and 53.98 (17)°] and of the Sn-bound benzene substituents [dihedral angles = 59.5 (2) and 45.77 (18)°, respectively]. The most prominent feature of the crystal packing is the formation of four-mol­ecule aggregates via O—H⋯O and O—H⋯N hydrogen bonds, in which the hy­droxy group is connected to a methanol mol­ecule which, in turn, is linked to a non-coordinating N atom. Weak C—H⋯π inter­actions also occur.

(E,E)-4-{4-[3-(4-Chloroanilino)-1-hydroxybut-2-enylidene]-3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-1-yl}benzenesulfonamide

The mol­ecule of the title compound, C20H19ClN4O4S, features a central pyrazole ring that possesses a benzene substituent, as well as a conjugated =C—C=C—Cmeth­yl substituent. The benzene ring is slightly twisted [dihedral angle = 7.7 (2)°] with respect to the five-membered ring; the mean plane of the zigzag =C—C=C—C fragment [torsion angle = 178.0 (4)°] is also slightly twisted [dihedral angle = 10.6 (4)°]. The amine and hy­droxy groups form intra­molecular hydrogen bonds. The amide group uses one of its H atoms to form a hydrogen bond to the sulfamyl O atom of an inversion-related mol­ecule. Adjacent dimers are further linked by an N—Hamido⋯Npyrazole hydrogen bond to generate a linear chain. The crystal studied is a nonmerohedral twin with a minor twin component of 25.6 (2)%.

1-(3-Chlorophenyl)-3-(4-nitrophenyl)urea

In the title compound, C13H10ClN3O3, prepared by the reaction of 1-chloro-3-isocyanato­benzene with 4-nitro­benzenamine, the two substituent benzene rings are roughly coplanar [inter-ring dihedral angle = 8.70 (7)°]. In the crystal, mol­ecules make cyclic inter­molecular associations through two urea–nitro N—H⋯O hydrogen bonds, forming a chain structure [give chain direction] in which there are also weak inter­molecular C—H⋯Cl inter­actions. The urea O atom has only intra­molecular aromatic ring C—H⋯O associations.

Ethyl 2-chloro-[2-(4-chlorophenyl)hydrazin-1-ylidene]acetate

The title compound, C10H10Cl2N2O2, features a planar Car—N(H)—N=C(Cl) unit [torsion angle = 5.5 (4)°] whose benzene substituent is coplanar with it [dihedral angle = 4.7 (4)°]; this unit is slightly twisted with respect to the carboxyl –CO2 fragment [dihedral angle = 2.2 (52)°]. The amino group acts as a hydrogen-bond donor to the carbonyl O atom of an adjacent mol­ecule; the hydrogen bond generates a helical polymer that runs along the b axis of the monoclinic unit cell.

3-Acetyl-2-methyl-4-phenylquinolin-1-ium chloride

An N—H⋯Cl hydrogen bond connects the ions in the title salt, C18H16NO+·Cl−. The quinolin-1-ium residue is almost planar (r.m.s. deviation = 0.020 Å) but both the acetyl group [O—C—C—C torsion angle = 62.73 (17)°] and adjacent benzene ring [C—C—C—C torsion angle = −104.06 (14)°] are twisted out of this plane; the acetyl and benzene substituents are non-parallel [dihedral angle = 66.16 (7)°]. The crystal packing is consolidated by C—H⋯O and C—H⋯Cl contacts.

(2E,4E)-1-(6-Chloro-2-methyl-4-phenyl-3-quinolyl)-5-phenylpenta-2,4-dien-1-one

In the title compound, C27H20ClNO, the quinoline ring forms a dihedral angle of 62.53 (5)° with the substituent benzene ring. In the crystal, inter­molecular C—H⋯Cl inter­actions link the mol­ecules into chains along the b axis. Inter­molecular C—H⋯N and C—H⋯O hydrogen bonds further consolidate the structure into a three-dimensional network. The unit cell contains four solvent-accessible voids, each with a volume of 35 Å3, but no significant electron density was found in them.

Stability and Reactivity of Grafted Cr(CO)3Species on MOF Linkers: A Computational Study

The possibility to modulate Cr(CO)(3) properties by grafting it onto metal-organic framework (MOF) linkers of different natures has been investigated using density functional methods. MOF linkers were modeled using clusters constituted by benzene rings doubly substituted in the para position. The effect of the electron-donor or electron-acceptor nature of benzene substituents on the stability of the (eta(6)-arene)Cr(CO)(3) adduct and on the shift of the CO bands has been considered. Different electron-donor (-NH(2), -CH(3), -OH, -COONa) and electron-acceptor (-F, -COOH, -CN, -CF(3)) substituents have been used and the results compared with the bare benzene. C(6)H(4)(COOZnOH)(2) and C(6)H(4)(Zn(4)O(13)C(6)H(5))(2) clusters have also been adopted as models of the MOF-5 benzene rings. The possibility of modulating the stability and the reactivity of Cr(CO)(3) species by grafting them to MOFs with different organic linkers was verified. In particular, this study indicates that electron-acceptor (e.g., C(6)H(4)(COOH)(2)) substituted MOF linkers facilitate the substitution of CO by incoming molecules, whereas the use of electron-donor ones (e.g., C(6)H(4)(OH)(2)) would improve the stability of the Cr(CO)(3) adduct and the ring acidity. Furthermore, an almost linear dependence of the Cr(CO)(3) binding energies on the calculated structural and vibrational features of the tricarbonyl was found, suggesting that the stability of the Cr(CO)(3) adduct can be inferred experimentally from vibrational and diffraction data. In the end, on the basis of the results obtained, it was possible to successfully explain the experimental shift of the CO IR stretching features of grafted Cr(CO)(3) on the UiO-66, CPO-27-Ni, and MOF-5 aromatic linkers and on the benzene rings of poly(ethylstyrene-co-divinylbenzene). The sign of the Delta nu(CO) shift with respect to C(6)H(6)Cr(CO)(3) has been found to be strongly dependent on higher/lower electron density on the ring.

N-(9H-Fluoren-9-ylidene)-4-methylaniline

In the title compound, C20H15N, the fluorene unit is essentially planar [r.m.s. deviation 0.0334 Å] and the benzene ring bound to the imine N atom bears a methyl group which is nearly coplanar [dihedral angle 0.5 (1)°]. The dihedral angle between the substituent benzene ring and the 9H-fluoren-9-imine unit is 71.1 (3)°. Inter­molecular π–π inter­actions between the benzene rings of adjacent fluorene units [centroid–centroid distance 3.8081 (13) Å] are present in the crystal structure, resulting in a one-dimensional supra­molecular architecture.

SERS as a probe for adsorbate orientation on silver nanoclusters

AbstractSurface‐enhanced Raman scattering (SERS) spectroscopy has been used to characterize multilayers of three isomeric aromatic compounds adsorbed on silver nanoclusters. The three structural isomers, all of which adsorb in the carboxylate form onto the silver nanoclusters, bind in two different geometries to the silver surface. Different molecular configurations correlate to differences in bonding strength of these molecules to the silver surface, which can be probed by SERS. For ortho‐hydroxybenzoic acid (salicylic acid), we observed red shifts of major SERS peaks in comparison to the normal Raman vibrations of nonadsorbed crystalline material. For this molecule the steric hindrance between the adjacent carboxylate and hydroxyl groups causes the carboxylate group to rotate from the common flat geometry of benzene substituents on surfaces and bond directly through one of the oxygen atoms to the surface. In this case, strong coordinative bonding between the carboxylate group and the metal surface causes the red shifts in the SERS peaks. For para‐, and meta‐hydroxybenzoic acid, the steric hindrance is less likely since the two functional groups are not at adjacent positions, and therefore these molecules adsorb on the silver surface in a totally flat geometry. For these molecules, in contrast to the ortho isomer, the CO2 interacts with the surface through an extended π bond, and these molecules are physically adsorbed in the common flat position. Therefore, for the meta and para substituents, we do not observe significant red shifts in the SERS spectrum. Copyright © 2009 John Wiley & Sons, Ltd.

4-(7-Acet-oxy-6-meth-oxy-4-methyl-2-oxo-2H-chromen-3-yl)phenyl acetate.

The title compound, C21H18O7, is an important inter­mediate in the synthesis of 3-(4-hydroxy­phen­yl)-4-methyl-6-meth­oxy-7-hydroxy­coumarin, which is a nonsteroidal analogue of 2-methoxy­estradiol (2-ME). The substituent benzene ring is not in the same plane as the coumarin ring system, with a dihedral angle of 66.88 (10)°. There are some weak inter­molecular C—H⋯O inter­actions. One carbonyl O atom is disordered over two sites, with occupancies of 0.6 and 0.4.

5,6-Dichloro-2-(2-fluorophenyl)isoindoline-1,3-dione

The crystal structure of the title compound, C14H6Cl2FNO2, exhibits C—H⋯π and π–π inter­actions, which generate C(3) chains in the [100] direction. The π–π inter­action occurs between the aromatic rings of isoindoline units, with a centroid–centroid distance of 3.672 Å and an inter­planar separation of 3.528 Å. The isoindoline unit is planar and inclined at an angle of 58.63 (18)° to the substituent benzene ring. The F atom is disordered over two positions, with refined occupancies of 0.669 (3) and 0.331 (3).

Rhodamine 6G hexa-chlorido-stannate(IV) acetonitrile disolvate.

In the title compound, bis({6-ethylamino-10-[2-(methoxycarbonyl)phenyl]-2,7-dimethylxanthen-3-ylidene}ethanaminium) hexachloridotin(IV) acetonitrile disolvate, (C27H29N2O3)2[SnCl6]·2C2H3N, the octa­hedral SnCl6 2− anion lies on an inversion center. The xanthene ring system is essentially planar, with an average deviation of 0.020 Å, and the substituent benzene ring forms a dihedral angle of 85.89 (2)° with it. The Sn—Cl distances are in the range 2.4237 (3)–2.4454 (3) Å. There are N—H⋯Cl hydrogen bonds between SnCl6 2− ions and rhodamine 6G cations as well as π–π stacking inter­actions between rhodamine 6G cations (inter­planar distance of 3.827 Å).

Quantitative Structure−Activity Relationship Studies of [(Biphenyloxy)propyl]isoxazole Derivatives. Inhibitors of Human Rhinovirus 2 Replication

The 50% cytotoxic concentration (CC50) in HeLa cells, the 50% inhibitory concentration (IC50) against human rhinovirus 2 (HRV-2), and the selectivity index (SI = CC50/IC50) of [(biphenyloxy)propyl]isoxazole derivatives were used to develop quantitative structure-activity relationships (QSAR) based on simplex representation of molecular structure. Statistic characteristics for partial least-squares models are quite satisfactory (R2 = 0.838 - 0.918; Q2 = 0.695 - 0.87) for prediction of CC50, IC50, and SI values and permit the virtual screening and molecular design of new compounds with strong anti-HRV-2 activity. The quality of prognosis for designed compounds was additionally estimated by analysis of domain applicability for each QSAR model. A hypothesis to the effect that terminal benzene substituents must have negative electrostatic potential and definite length (approximately 5.5-5.6 A) to possess strong antiviral activity has been suggested. The quality of developed analysis, i.e., high level of antiviral action of three new designed compounds, has been confirmed experimentally.

3-(4-Fluorophenyl)-2-morpholinoquinazolin-4(3H)-one

The title compound, C18H16FN3O2, was obtained via the aza-Wittig reaction. The quinazolinone ring system is almost planar and makes a dihedral angle of 67.09 (8)° with the substituent benzene ring. The structure is stabilized by a weak C—H⋯O hydrogen bond and C—H⋯π inter­actions.

Ortho-Selective C−H Activation of Substituted Benzenes Effected by a Tungsten Alkylidene Complex without Substituent Coordination

Gentle thermolysis of the bis(neopentyl) complex Cp*W(NO)(CH2CMe3)2 (1) at 70 °C in various substituted benzenes results in the loss of neopentane and the generation of the transient alkylidene complex Cp*W(NO)(CHCMe3) (A), which subsequently effects single C−H bond activations of the benzenes. These activations exhibit a pronounced selectivity for the C−H linkages ortho to the benzene substituents. Thus, thermal reactions of 1 with C6H5X lead to the preferential formation of the corresponding Cp*W(NO)(CH2CMe3)(o-C6H4X) complexes, the ortho-selectivity, i.e., X = F > OMe > Cl > Br > C⋮CPh, diminishing as the steric demands of the substituents increase. Consistently, thermolyses of 1 in o-C6H4X2 afford Cp*W(NO)(CH2CMe3)(2,3-C6H3X2) complexes with 98% selectivity when X = F and 82% selectivity when X = Cl. Similarly, the principal organometallic products resulting from the thermolyses of 1 in m-C6H4X2 are the ortho-para-activated isomers Cp*W(NO)(CH2CMe3)(2,4-C6H3X2) with 84% selectivity when X = F and 89% selectivity when X = Cl. Finally, thermolyses of 1 in para-disubstituted benzenes p-C6H4XY (X = F or OMe, Y = Cl or OMe) again reveal that the ortho-directing abilities of the substituents diminish in the order F > OMe > Cl. Some mechanistic insights into these activation processes have been obtained by monitoring of the early stages of the thermolysis of 1 in chlorobenzene by 1H NMR spectroscopy. This monitoring reveals that the selectivity of the alkylidene intermediate A for forming the ortho-activated isomer is thermodynamic rather than kinetic in nature. Thus, the meta- and para-activated isomers are formed initially, but then convert to the ortho-activated product. The principal organometallic complexes resulting from ortho-C−H activations are formally 16-electron species in which there are no interactions between the tungsten centers and the Lewis-basic benzene substituents. Instead, the Lewis-acidic tungsten centers engage in intramolecular agostic interactions with the methylene C−H bonds of their neopentyl ligands to acquire some additional electron density. Being coordinatively and electronically unsaturated, these tungsten complexes react readily with added Lewis bases. Thus, treatment of Cp*W(NO)(CH2CMe3)(o-C6H4F) with Et4NCN and CO produces [Et4N]+[Cp*W(NO)(CH2CMe3)(CN)(o-C6H4F)]- and Cp*W(NO)(η2-C(O)CH2CMe3)(o-C6H4F), respectively, and the solid-state molecular structure of the latter complex has also been established by a single-crystal X-ray crystallographic analysis.

Inhibitors ofTrypanosoma cruziTrypanothione Reductase Revealed by Virtual Screening and Parallel Synthesis

In an approach to discover new inhibitors of trypanothione reductase from Trypanosoma cruzi, the causative agent of Chagas' disease, a virtual high-throughput screening was performed. Two structurally new types of inhibitors emerged, the antimicrobial chlorhexidine {1,1'-hexamethylenebis[5-(4-chlorophenyl)biguanide]}, a linear competitive inhibitor (K(i) = 2 +/- 1 microM), and a piperidine derivative acting as mixed inhibitor (K(i) = 6.2 +/- 2 microM and K(i)' = 8.5 +/- 2 microM). Neither compound interferes with human glutathione reductase. Based on chlorhexidine, different series of compounds were synthesized and studied as inhibitors of T. cruzi trypanothione reductase. Most efficient derivatives were three bis(amidines) showing mixed type inhibition with K(i,slope) and K(i,int) values of 2-5 microM and 16-47 microM, respectively. Although these compounds did not exert an improved inhibitory potency compared to chlorhexidine, the change from competitive to mixed-type inhibition is advantageous, since substrate accumulation does not overcome inhibition. Remarkably, all three derivatives carried two copies of an identical 2-methoxy-4-methyl-1-(phenylmethoxy)benzene substituent.

Influence of Stacking on Hydrogen Bonding: Quantum Chemical Study on Pyridine−Benzene Model Complexes

The present work focuses on the influence of aromatic stacking on the ability of an aromatic nitrogen base to accept a hydrogen bond. Substituent effects were studied at the MP2 level for 10 complexes of a substituted benzene stacked with pyridine in a parallel offset conformation. The interaction energies between each substituted benzene and pyridine were analyzed in terms of Hartree−Fock, correlation, and electrostatic contributions. It appears that the basicity of pyridine is directly related to the electrostatic interaction between the cycles. It increases with increasing electron donating character of the benzene substituents. Also, density functional theory based descriptors such as global and local hardnesses and the benzene ring polarizability are found to adequately predict the interaction energy. These findings may be important in the study of DNA/RNA chains.

EFFECT OF RING SIZE ON THE COMPLEXATION AND DECOMPOSITION OF BENZENEDIAZONIUM ION IN THE PRESENCE OF CROWN ETHERS IN 1,2-DICHLOROETHANE AND THE GAS PHASE

The host–guest complexation and the kinetics of the thermal dediazoniation of benzenediazonium tetrafluoroborate in the presence of unsubstituted and (di)benzene- and dicyclohexane-substituted crown ethers containing 4–10 oxygen atoms were studied by UV spectrophotometry in 1,2-dichloroethane at 40°C. The complexation equilibrium constants K and the stabilizing ability of the complexation (k2/k1) were calculated by a kinetic method. Complexation in the gas phase was observed and characterized by fast atom bombardment mass spectrometry (FAB-MS). All complexing agents except 12-crown-4 formed 1:1 complexes [crown ether–PhN2]+ under FAB conditions. The complexation caused a hypsochromic shift Δλmax in the UV spectrum of the benzenediazonium salt, which was largest for hosts containing six oxygen atoms. The thermodynamic and kinetic stability were much greater for insertion-type complexes containing six or more oxygen atoms in the host molecule than for the charge-transfer complexes formed with 15-crown-5. In contrast, 12-crown-4 destabilized benzenediazonium ion owing to the increase in homolytic dediazoniation. 21-Crown-7 was the strongest complexing and stabilizing agent for benzenediazonium ion; with a larger hole size in the host the effects weakened. The effects of benzene and cyclohexane substituents in crown ethers on the thermodynamic and kinetic stability were small compared with the effects of the number of oxygen atoms. © 1997 by John Wiley & Sons, Ltd.

Liquid-phase photofluorination with elemental fluorine. Part III. Synthesis of perfluorocycloalkyl ethers with/without a chlorine substituent

Liquid-phase photofluorination (LPPF) of 2-phenyl-2-methoxyhexafluoropropane 1 gave the desired F-2-cyclohexyl-2-methoxypropane, 2, in 21% yield. An unusual rearranged product, F-2-cyclohexylmethyl isopropyl ether, 4, and a degradation product, F-2-cyclohexylpropane, 3, were also produced in 10 and 20% yields, respectively. A plausible reaction mechanism for the formation of the rearranged product 4 was presented. The Cl-containing ethers with cyclic structures, 2-chlorohexafluorocyclopentenyl cyclopentyl ether, and 2-chlorohexafluorocyclopentenyl 2,2,3,3,4,4,5,5-octafluoro- n-pentyl ether were also perfluorinated by the LPPF method to give the corresponding Cl-containing F-ethers in fair yields. The total retention of the chlorine atom through perfluorination and the ability to have a benzene substituent on the substrate are benificial features of this novel perfluorinating method.