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At least 19 recordsLinked to original sources
PubMed2006

The absorption spectra of anisole-h8, anisole-d3 and anisole-d8. The assignment of fundamental vibrations in the S0 and the S1 states.

The REMPI spectra of anisole-h8, anisole-d3 and anisole-d8 have been measured. The assignment of the fundamental vibrations of anisole in the S(1) state is supported by quantum chemical model calculations, the isotopic shifts, the comparison with the frequencies of corresponding vibrations in other monosubstituted benzenes, especially phenol, and the overtones, combinations and progressions observed in the spectrum of anisole-h8. The frequencies of the 42 fundamental vibrations of anisole in the S(1) state are evaluated and compared with the frequencies of the corresponding vibrations in the electronic ground state. Some assignments given earlier in the literature have been revised.

Absorption↗
PubMed2006

High resolution electronic spectra of anisole and anisole-water in the gas phase: hydrogen bond switching in the S1 state.

Rotationally resolved S(1)<--S(0) electronic spectra of anisole and its hydrogen bonded complex containing one water molecule have been obtained. The results provide evidence for an "in-plane" complex in which the water molecule is attached via two hydrogen bonds to the anisole molecule, a donor O-H- - -O(CH(3)) bond and an acceptor H-O- - -H(ring) bond. Analysis of the subbands that appear in the spectrum of the complex suggests that hydrogen bond "switching" occurs when the complex absorbs light. The former O-H- - -O(CH(3)) bond is stronger in the ground (S(0)) state, whereas the latter H-O- - -H(ring) bond is stronger in the excited (S(1)) state. Dynamical consequences of this phenomenon are discussed.

Journal Article↗
PubMed2006

Theoretical and spectroscopic study of the effect of ring substitution on the adsorption of anisole on platinum.

The adsorption of anisole, 3,5-dimethylanisole, and 3,5-bis-(trifluoromethyl)-anisole on Pt(111) was studied theoretically and compared to the adsorption of benzene using relativistically corrected density functional theory. A cluster of 31 platinum atoms was used to simulate the surface. The three anisoles were found to be less strongly adsorbed than the parent molecule benzene, 3,5-bis-(trifluoromethyl)-anisole showing weakest adsorption, with an adsorption energy of only one-third that of benzene. The theoretical study was complemented by in situ ATR-IR spectroscopy of the adsorption of the anisole derivatives on a polycrystalline Pt film. The spectroscopic study indicated that the adsorption strength of the anisoles follows the same order as predicted by the calculations. In addition, catalytic hydrogenation tests showed that the propensity to aromatic ring hydrogenation can also be correlated to the mode and strength of adsorption of the anisoles. The degree of saturation followed the same order as the adsorption strength found by the calculations and indicated by spectroscopy. Although 3,5-dimethyl substitution on anisole resulted in only a partial loss of adsorption energy and reactivity toward ring hydrogenation as compared to anisole, the substitution by CF(3) groups led to a large loss of adsorption energy and complete loss of reactivity toward aromatic ring saturation. Along with the study of the substituent effect on the adsorption of aromatic molecules, the correlation between adsorption and propensity to saturation of aromatic substrates could be corroborated.

Journal Article↗
PubMed2006

Alkali-metal-mediated zincation of anisole: synthesis and structures of three instructive ortho-zincated complexes.

The new concept of alkali-metal-mediated zincation (AMMZ), formally a zinc-hydrogen exchange reaction but one that requires the participation of an alkali metal, is applied here to the alkyl aryl ether anisole, an important molecule for studying directed ortho-metalation (DoM) chemistry. Treating one molar equivalent of anisole with the lithium dialkyl-TMP zincate reagent [THF.Li(mu-TMP)(mu-tBu)Zn(tBu)] (1) in hexane solution affords the mono-ortho-zincated complex [THF.Li(mu-TMP)(mu-o-C6H4OMe)Zn(tBu)] (2), which establishes that 1 functions as an alkyl base although previously it was regarded as an amido (TMP) base in other DoM applications. Treating two molar equivalents of anisole with 1, and increasing the reaction time, affords the bis-ortho-zincated complex [THF.Li(mu-TMP)(mu-o-C6H4OMe)Zn(o-C6H4OMe)] (3), which establishes that 1 can also function as a dual alkyl base. Omitting THF and rerunning the reaction with one or two molar equivalents of anisole affords [Ph(Me)O.Li(mu-TMP)(mu-o-C6H4OMe)Zn(tBu)] (4), which remarkably contains a combination of neutral and ortho-deprotonated anisole ligands. On isolating crystalline 4 from solution and adding THF, it converts to 2 and then to 3 on further stirring of the solution, as determined by NMR studies. This fact, along with other observations, would suggest that a complex-induced proximity effect does not need to be invoked to explain the observed zincation of anisole. The crystal structures of 2-4 are presented, as are their 1H, 13C, and 7Li NMR spectra recorded in C6D6 solution.

Journal Article↗
PubMed1992

Effects of oxygen concentration on the metabolism of anisole homologues by rat liver microsomes.

1. The effects of oxygen concentration were studied on the metabolic pathways of anisole homologues (anisole, phenetole and isopropoxybenzene) catalysed by liver microsomes from phenobarbital-treated rats. 2. With increase of oxygen concentration, the rate of anisole o-hydroxylation reached a plateau at about 35 microM O2, while the rates of O-demethylation and aromatic p-hydroxylation were still increasing at 223 microM O2 (air). 3. The rates of all three metabolic reactions of phenetole reached plateau levels at about 80 microM O2. 4. The rates of all three metabolic reactions of iso-propoxybenzene were still increasing as 223 microM O2 (air). 5. The ratio of aromatic p-hydroxylation or O-dealkylation to aromatic o-hydroxylation decreased in anisole metabolism, and showed no uniform change in phenetole and isopropoxybenzene metabolism with decreasing oxygen concentration. 6. The ratio of aromatic p-hydroxylation to O-dealkylation was essentially constant over the range of oxygen concentration studied in anisole and phenetole metabolism, while in iso-propoxybenzene metabolism the ratio was different between higher and lower oxygen concentrations than 60 microM. 7. This series of compounds with increasing chain length did not show homologous changes in rates of product formation or O2 dependent of product formation.

Animals↗
PubMed2005

NMR spectrometric studies of complexation of [60]fullerene with series of anisoles.

Detailed (1)H and (13)C NMR spectrometric studies have been carried out to gain insight into the nature of molecular interactions of the electron donor-acceptor (EDA) complexes of [60]fullerene with a series of anisoles, namely, anisole, m-bromoanisole, and p-bromoanisole. [60]Fullerene has been shown to form 1:1 adducts with the above series of anisoles. Formation constants (K) for all the complexes have been determined from the systematic variation of the NMR chemical shifts of specific protons of the anisoles in the presence of [60]fullerene. The K values of [60]fullerene/anisole, [60]fullerene/m-bromoanisole, and [60]fullerene/ p-bromoanisole complexes yield good estimates of the Hammett rho constant for the complexation reaction. To the best of our knowledge, this paper reports for the first time a very fruitful technique by which the concentrations of EDA complexes can be estimated from systematic variations of the (13)C NMR signal.

Anisoles↗
PubMed1996

Determination of biogenic halogenated methyl-phenyl ethers (halogenated anisoles) in the picogram m(-3) range in air.

Halogenated anisoles (methyl-phenyl ethers) appear to be ubiquitous organic trace compounds in the environment. An analytical method is presented for analyzing the altogether 134 congeners of chloro-, bromo- and mixed bromochloro-anisoles on an isomer-specific basis in air. High volume sampling (20 m(3) per hour) is carried out by adsorption, using a mixture of silica gel 60 and ENVI-Carb. The preseparation of the anisoles is achieved by NP-LC on Florisil (a magnesium silicate). The interference by volatile n-alkyl nitrates in the electron-capture detection can be avoided by a LC-preseparation on a carboneous phase. The isomer-specific separation and detection is performed by HRGC-ECD and HRGC-MS-SIM. A structure-specific systematic numbering of the 134 congeners of the chloro-, bromo- and bromochloro-anisoles is suggested. The retention data are given of 16 chloroanisoles, 10 bromoanisoles and 27 bromo-chloroanisoles on three stationary phases with different polarity.

Journal Article↗
PubMed2001

Halogenated methyl-phenyl ethers (anisoles) in the environment: determination of vapor pressures, aqueous solubilities, Henry's law constants, and gas/water- (Kgw), n-octanol/water- (Kow) and gas/n-octanol (Kgo) partition coefficients.

Halogenated methyl-phenyl ethers (methoxybenzenes, anisoles) are ubiquitous organics in the environment although they are not produced in industrial quantities. Modelling the fate of organic pollutants such as halogenated anisoles requires a knowledge of the fundamental physico-chemical properties of these compounds. The isomer-specific separation and detection of 60 of the 134 possible congeners allowing an environmental fingerprinting are reported in this study. The vapor pressure p0(L) of more than 60 and further physico-chemical properties of 26 available congeners are given. Vapor pressures p0(L), water solubilities S(L)W, and n-octanol/water partition coefficients Kow were determined by capillary HR-GC (High Resolution Gas Chromatography) on a non-polar phase and by RP-HPLC (Reversed Phase High Performance Liquid Chromatography) on a C18 phase with chlorobenzenes as reference standards. From these experimental data the Henry's law constants H, and the gas/water Kgw and gas/n-octanol Kgo partition coefficients were calculated. We found that vapor pressures, water solubilities, and n-octanol/water partition coefficients of the halogenated anisoles are close to those of the chlorobenzenes. A similar environmental fate of both groups can, therefore, be predicted.

Anisoles↗
PubMed2005

Determination of the odor threshold concentrations of chlorobrominated anisoles in water.

Trihalophenols, which are drinking water disinfection byproducts (DBPs) formed by chlorination or chloramination practices, can be biomethylated into trihalogenated anisoles. These latter compounds have traditionally been suspected of causing odor episodes in drinking water around the world. The odor threshold concentration (OTC) of mixed chlorobrominated anisoles, which were previously synthesized, was determined by flavor profile analysis (FPA) performed by an experienced panel trained to identify odors and tastes in water. The odor threshold amount (OTA) was evaluated by using a gas chromatograph equipped with olfactometry (GC-O) and electron capture detectors (ECD). FPA results for mixed chlorobromoanisoles gave a theoretical OTCs range from 2 to 30 ng/L, the 2,6-diBr-3Cl-anisole being the most odorous compound. Rubber is the general descriptor described by panelists for these compounds, although earthy and musty are the following most cited descriptors.

Anisoles↗
PubMed1977

[O-demethylation kinetics of anisole and p-chloroanisole by cumene hydroperoxide and cytochrome P-450 of liver microsomes].

The kinetics of anisole oxidation by microsomes and tertiary butylhydroperoxide have been studied in phosphate buffer (pH 7,4) at 37 degrees C. About 20% of the substrate are shown to undergo demetylation and about 80% were hydroxylated in the p-position. The kinetics of the oxidative o-demethylation of anisole and p-chloroanisole by cumene hydroperoxide and hepatic microsomes has been studied within the temperature range of 20--37 degrees C. The catalytic rate constants for o-demethylation of anisole and chloroanisole have been determined in a general form to equal 2,04.10(7) exp (--11400/RT) and 5,5.10(7) exp (--11800/RT) sec-1, respectively. The reactions of o-demethylation and hydroperoxide have been proved to be independent. The data obtained are indicative of the electrophilic nature of the hydroxylating agent in the system "microsomes-hydroperoxide".

Animals↗
PubMed1996

A Density Functional Study of Substituent Effects on the O-H and O-CH(3) Bond Dissociation Energies in Phenol and Anisole.

The substituent effects on O-H and O-CH(3) bond dissociation energies for a series of 18 para-substituted phenols (p-XC(6)H(4)OH) and 11 para-substituted anisoles have been studied using the density functional method in order to understand the origin of these effects. The calculated substituent effects agree well with experimental measurements for phenols but are substantially larger than the reported values for anisoles. Both ground-state effect and radical effect contribute significantly to the overall substituent effect. An electron-donating group causes a destabilization in phenols or anisoles (ground-state effect) but a stabilization in the phenoxy radicals (radical effect), resulting in reduced O-R bond dissociation energy. An electron-withdrawing group has the opposite effect. In most cases, the radical effect is more important than the ground-state effect. There is a good correlation between the calculated radical effects and calculated variations in charge and spin density on the phenoxy oxygen. This supports the concept that both polar and spin delocalization effects influence the stability of the phenoxy radical. While almost every para-substituent causes a stabilization of the phenoxy radical by spin delocalization, electron-donating groups stabilize and electron-withdrawing groups destabilize the phenoxy radical by the polar effect.

Journal Article↗
PubMed1997

Osmium-Promoted Electrophilic Substitution of Anisoles: A Versatile New Method for the Incorporation of Carbon Substituents.

A structurally and electronically diverse set of anisoles are dihapto-coordinated to the pi-base pentaammineosmium(II) and treated with a variety of carbon electrophiles (e.g. Michael acceptors, acetals). After deprotonation of a 4H-anisolium intermediate with a tertiary amine base, C(4)-substituted anisole complexes are isolated. The functionalized arenes are removed from the metal center either by mild heating or treatment with an oxidant (e.g. AgOTf, DDQ, CAN). The resulting substituted anisoles are isolated with yields ranging from 55-95%.

Journal Article↗
PubMed1978

Variation of isomer distribution in electrophilic nitration of toluene, anisole, and o-xylene: Independence of high regioselectivity from reactivity of reagent.

The nitration of toluene and anisole was studied with nitrating systems of varying reactivity. High regioselectivity of ortho-para over meta substitution was maintained in all nitrations, regardless of the reactivity of the nitrating system. At the same time, the amount of meta substitution stayed low (3% or less), even when the fast reactions may have reached the encounter-controlled limit. Because the nitration of o-xylene, in which both ring positions are activated by the effect of a methyl group, also does not show any diminishing of regioselectivity, the possibility of a dual mechanistic pathway, in which the activated position would react by a fast, encounter-controlled path, whereas the nonactivated meta position by a slower sigma-type path, can be ruled out. The data unambiguously prove that the high regioselectivity of electrophilic aromatic nitration is independent of the reactivity of the reagent, because no significant increase of meta substitution of toluene or anisole was observed, regardless of the activity of the nitrating system. No selectivity-reactivity relationship is thus evident and the ortho-para directing effect of primary substituents over meta substitution is always maintained. The variation in the amount of the meta isomer, up to the observed limit of about 3% in the case of toluene and <2% for anisole, is probably significant but, at the present time, cannot be quantitatively evaluated with the +/-0.5% overall reproducible accuracy of the nitrations. Steric factors, such as increasing bulkiness of the nitrating agent, also can affect the ortho-para isomer ratios but are not considered to be the only reason for the observed variations, which reflect the specific nitrating systems, affecting the nature and position of the transition state of highest energy on the reaction pathway.

Journal Article↗
PubMed2004

Michael addition reactions with eta2-coordinated anisoles: controlling the stereochemistry of the para and benzylic carbons.

Several eta(2)-coordinated anisole complexes were treated with various Michael acceptors in the presence of a Lewis or Bronsted acid to generate stable 4H-anisolium complexes. These reactions were found to proceed with high stereochemical control with predictable outcomes, provided that the moderate acid (NH(2)Ph(2))OTf was used and the complex was dissolved in an acidic solution. The stereochemistry is shown to originate from an unexpectedly high preference for one coordination diastereomer of the anisole complex in the solid state and a Diels-Alder like transition state for the Michael reaction.

Anisoles↗
PubMed1983

Residues of polychlorinated phenols and anisoles in broilers raised on contaminated woodshaving litter.

Broilers were raised for 8 weeks on litter made up of woodshavings containing high (700 micrograms/g) levels of contamination with polychlorinated phenols (PCP). The PCP levels declined in the litter over the test period while polychlorinated anisoles (PCA) increased in the highly contaminated litter. Final weights of the birds was only slightly different; however, feed conversion was slightly higher for those birds raised in the highly contaminated pens. Panelists rated the cooked samples from the birds raised on highly contaminated litter significantly lower for flavor and overall acceptability than either of the lower PCP level treatments. Residues of the odiferous pentechloroanisole were present in muscle and fat of the birds raised on the highly contaminated litter; however, residues in muscles of the birds on low level contaminated litter could not be detected. Polychlorinated anisoles were present in the fat of birds raised on normal litter but adjacent to the contaminated pens.

Animals↗
PubMed1981

Determination of the antioxidant 3-tert.-butyl-4-hydroxy-anisole in rat-plasma using high-resolution gas chromatography-mass spectrometry.

A method is described for the determination of the antioxidant 3-tert.-butyl-4-hydroxy-anisole in rat plasma using high-resolution capillary gas chromatography-mass spectrometry with selective ion monitoring. Following the addition of the isomer 2-tert.-butyl-4-hydroxy-anisole, used as an internal standard, extraction was made with n-hexane and the extract derivatized with heptafluorobutyric anhydride. The gas chromatographic separation was carried out on a SE-52 fused silica capillary column and the derivatized 3-tert.-butyl-4-hydroxyanisole and its isomer detected by recording the intensities of their common fragment ion at m/e 361. The sensitivity of the method allowed the antioxidant to be measured in 0.1-ml rat plasma samples down to a level of 10 ng/ml with a high degree of specificity and accuracy. The method has been applied to a preliminary pharmacokinetic study in rats after oral dosage.

Animals↗
PubMed2000

A mechanistic study of the FeO+-mediated decomposition pathways of phenol, anisol, and their thio analogues.

The gas-phase oxidations of phenol, anisol, thiophenol, and thioanisol by 'bare' FeO+ are examined by using Fourier transform-ion cyclotron resonance (FT-ICR) and tandem mass-spectrometry. Reaction mechanisms are derived on the basis of isotope-labeling experiments, MS/MS studies, and comparison with structural isomers, that is ions formed by independent routes. The chemistry of all substrates is determined by the functional groups, whereas reactions typical of unsubstituted benzene with FeO+ are suppressed. For phenol and thiophenol, four-membered metallacycles are obtained concomitant with a regioselective loss of water, which involves the O atom from the FeO+ entity and hydrogen atoms originating from the functional group and from the ortho position of the ring. C-H bond cleavage of the methoxy group (kH/kD = 2.0) is rate-contributing for the degradation of metastable anisol/FeO+, which is featured by highly regioselective losses of H2O, HCO, H2CO, and [C,H2,O2]. In the oxidation of thioanisol, two different C-H bond activation mechanisms are operating, resulting in the elimination of [Fe,H,O,S] concomitant with the formation of the benzyl cation (kH/kD = 4.7), and loss of water (kH/kD = 2.5). The reactions of independently generated, formal S- and C-oxidation intermediates of thioanisol indicate the occurrence of extensive structural isomerizations prior to dissociation. For anisol and thioanisol, analogies and differences between oxidation reactions catalyzed by the enzyme cytochrome P-450 in the condensed phase and those observed for the gas-phase model FeO+ are discussed.

Deuterium↗