Effect Of Aromatic Substitution Research Articles

Effect of aromatic substitution on the cure reaction and network properties of anhydride cured triphenyl ether tetraglycidyl epoxy resins

A systemic study of the impact of aromatic substitution on the reaction rate and network properties of the isomers of a tetraglycidylaniline triphenyl ether epoxy resin cured with anhydride hardeners is presented here. The epoxy resins synthesized in this work were based upon N,N,N,N‐tetraglycidyl bis(aminophenoxy)benzene (TGAPB), where the glycidyl aniline and ether groups change from being all meta (133 TGAPB), to meta and para (134 TGAPB), and finally to an all para substituted epoxy resin (144 TGAPB). Increasing para substitution increased reaction rate, promoted the onset of vitrification and increased epoxide conversion. Thermal properties such as glass transition temperatures (Tg) and coefficients of thermal expansion (CTE) both increased consistently with increasing para substitution, although thermal stability as measured via thermogravimetric analysis decreased. Mechanical properties also varied systematically with flexural strength and ductility increasing with increased para substitution, while the modulus decreased. Indeed, the ductility almost doubled, as measured by the work of fracture and displacement at failure highlighting the importance of substitution on properties.

Effect of aromatic substitution on the kinetics and properties of epoxy cured tri‐phenylether amines

ABSTRACTThe reaction kinetics and structure property relationships of isomeric tri‐aromatic ether‐linked amines based on the structure bis (aminophenoxy) benzene, cured with diglycidyl ether of bisphenol F (BisF) are investigated in this study. Reaction kinetics are explored using rheological and calorimetric measurements, whereas structure property relationships are determined from their flexural properties, dynamic mechanical properties (DMTA), and thermogravimetric analysis (TGA). A BisF network cured with 4,4 diamino diphenyl sulphone (44 DDS) is used as a benchmark to represent a commercially available high‐performance resin system. Varying the substitution of the ether linkages on the aromatic groups from ortho, meta to para was found to have a significant impact on reactivity and network properties after cure. The variations are explained in terms of inductive and resonance effects primarily acting on the outer aromatic rings. Interestingly, however, these same effects acting on the central aromatic ring also impact upon reactivity despite their proximity from the amines. Mechanical and thermal properties are explained by changes in the short‐range molecular mobility within the network architecture such as phenylene rotations or π flips and are experimentally validated from the breadth and position of the subambient γ relaxations. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47383.

Effect of Aromatic Substitution of Curcumin Nanoformulations on Their Stability.

Curcumin, a poorly water-soluble bioactive compound, was successfully loaded into three different aromatic contents of hydroxypropylmethacrylamide (HPMA)-based polymeric micelles in order to develop water-soluble curcumin nanoformulations (Cur-Nano). The stability study of Cur-Nano was done by keeping the formulations at 4, 30, and 40 °C for 90 days. The physical appearance, curcumin remaining, and particle size of Cur-Nano were examined by visual inspection, high-performance liquid chromatography, and dynamic light scattering, respectively. After the storage period, the Cur-Nano composed of 100% aromatic-substituted polymer exhibited the highest stability of curcumin (80% of curcumin remaining) with a similar particle size as measured on the first day (50–60 nm) in all storage conditions. Curcumin in Cur-Nano composed of 25% and 0% aromatic-substituted polymer was significantly less stable accordingly. The results suggested that aromatic substitution to HPMA-based polymeric micelles can significantly enhance the stability of the loaded curcumin, considerably due to the π-π stacking interactions between the aromatic groups of curcumin and the polymer. It is concluded that curcumin-loaded polymeric micelles with high substituted aromatic content can be promising candidates with good storage stability for further clinical evaluations.

Transformations of Ferric Chloride-Generated Stilbene Cation Radicals. The Effect of Aromatic Substitution and a Comparison with Anodic Oxidation.

A systematic study on the FeCl3-induced oxidation of 1,2-diarylalkenes was carried out with the focus on the variation of product type as a function of aromatic substitution, as well as to compare the reactivity of stilbene cation radicals generated via Fe(III) oxidation with those generated by anodic oxidation. The aromatic substituents were found to fall into three main categories, namely those that give rise to tetralins and/or dehydrotetralins, those that give products possessing pallidol and ampelopsin F-type carbon skeletons, and last, those that give rise to trimeric products, indanes, and dehydrotetralins/tetralins. The latter are those stilbenes with a para-methoxy substituent in one ring and a para- or meta-EWG (CF3, NO2, Cl, F) in the other, and represent the most prominent departure when compared with the behavior of the same stilbenes under the conditions of anodic oxidation. Reaction pathways to rationalize the formation of the different products are presented.

Effects of Aromatic Substitution on the Photodimerization Kinetics of β-trans Cinnamic Acid Derivatives Studied with 13C Solid-State NMR

In our efforts to study photodimerizations in the solid state, we present data on the influence of the position of aromatic substitution by bromine on the photodimerization rate in cinnamic acid de...

Effect of aromatic substitution in aniline on the properties of polyaniline

Substitution in aniline has tremendous effect in the synthesis of poly(substituted anilines) as well as in their properties. In this investigation polyaniline (PANI), poly( m-nitro aniline) (PMNA), poly( m-amino phenol) (PMAP) and poly( o-ethyl aniline) (POEA) were synthesized by oxidative polymerization under identical conditions. Different properties were measured and compared with PANI to find out the presence of electron donating –OH group, electron withdrawing –NO 2 group and less effecting ethyl group on the properties of poly(substituted anilines). It was found that presence of any type of substitution in the benzene ring of aniline increases the solubility of the resulted polymer but reduces the yield, degree of polymerization, thermal stability, electrical and thermal conductivity. The colors, bulk density, particle size, percentage of crystallinity vary considerably depending on the nature of substitution.

Relative reactivity and kinetic pattern of aniline and N‐methylaniline as nucleophiles in aromatic substitution (SNAr) reactions

AbstractKinetic results are reported for the reactions of 4‐nitrophenyl‐2,4,6‐trinitrophenyl ether 3 with aniline and N‐methylaniline in dimethyl sulphoxide, acetonitrile, methanol, and benzene. The reactions gave the expected 2,4,6‐trinitrodiphenylamine and were base catalyzed in all the solvents. Both nucleophiles showed the same kinetic pattern under the same reaction conditions but aniline was found to be considerably more reactive than N‐methylaniline. The greater catalytic efficiency of aniline over N‐methylaniline is consistent with the proton transfer mechanism of the base‐catalyzed step. Dichotomy of amine effects in aromatic substitution (SNAr) reactions is discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 188–196, 2004

Computational and Experimental Studies of the Effect of Substituents on the Singlet−Triplet Energy Gap in Phenyl(carbomethoxy)carbene

The effect of aromatic substitution on the singlet-triplet energy gap in substituted phenyl(carbomethoxy)carbene (X-Ph-C-CO(2)CH(3), PCC) has been explored by time-resolved infrared (TRIR) spectroscopy and gas-phase computational methods. The ground state of para-substituted PCC is calculated to change from the triplet state in p-NO(2)-PCC (Delta G(ST) = 6.1 kcal/mol) to the singlet state in p-NH(2)-PCC (Delta G(ST) = -2.8 kcal/mol). The absence of solvent perturbation in the TRIR spectra of p-N(CH(3))(2)-PCC (which should have electronic properties similar to p-NH(2)-PCC) and parent PCC is consistent with their ground states lying > +/-2 kcal/mol from the next available electronic state, in line with the computational results. The observation of solvent perturbation in the TRIR spectra of p-OCH(3)-PCC and p-CH(3)-PCC implies that their ground states lie < +/-1 kcal/mol from their next available electronic state. This is in agreement with our computational results, which predict a gas-phase Delta G(ST) of -0.8 and 1.6 kcal/mol for p-OCH(3)-PCC and p-CH(3)-PCC as compared to Delta G(ST) values of -3.9 and -1.3 kcal/mol from polarizable continuum model (PCM) calculations with acetonitrile as a solvent. Gas-phase computational results for the meta- and ortho-substituted PCC species are also presented, along with selected linear free energy (LFE) relationships for the para and meta species.

Effect of aromatic substitution on phase behavior of blends of halogenated polystyrene and conventional polystyrene

Miscibility phase behavior in blends of poly(bromostyrene) with polystyrene (PS) has been investigated by means of time-resolved light scattering, optical microscopy, and DSC. Cloud point phase diagrams of blends of conventional PS with poly-(2-bromostyrene) (P2BrS), poly-(3-bromostyrene), and poly-(4-bromostyrene) of comparable molecular weights were established by light scattering. Of particular interest is the fact that ortho, meta, and para substitutions in the styrenic aromatic rings of poly(bromostyrene) show profound effects on the composition–temperature phase diagrams of their blends with PS, exhibiting a lower critical-solution temperature (LCST), an upper critical solution temperature (UCST), and combined LCST/UCST diagrams, respectively. Poly-(2-chlorostyrene) exhibits an LCST behavior very close to that of the P2BrS blend, suggesting that these types of halogen atoms may be inconsequential to phase behavior. A similar study has been extended to a PS blend containing commercial brominated PS (66 mol % bromine substitution) to determine what location of bromine substitution is crucial for miscibility enhancement in the flame-retardant brominated PS blends. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1605–1615, 2001

Effect of aromatic substitution on phase behavior of blends of halogenated polystyrene and conventional polystyrene

AbstractMiscibility phase behavior in blends of poly(bromostyrene) with polystyrene (PS) has been investigated by means of time‐resolved light scattering, optical microscopy, and DSC. Cloud point phase diagrams of blends of conventional PS with poly‐(2‐bromostyrene) (P2BrS), poly‐(3‐bromostyrene), and poly‐(4‐bromostyrene) of comparable molecular weights were established by light scattering. Of particular interest is the fact that ortho, meta, and para substitutions in the styrenic aromatic rings of poly(bromostyrene) show profound effects on the composition–temperature phase diagrams of their blends with PS, exhibiting a lower critical‐solution temperature (LCST), an upper critical solution temperature (UCST), and combined LCST/UCST diagrams, respectively. Poly‐(2‐chlorostyrene) exhibits an LCST behavior very close to that of the P2BrS blend, suggesting that these types of halogen atoms may be inconsequential to phase behavior. A similar study has been extended to a PS blend containing commercial brominated PS (66 mol % bromine substitution) to determine what location of bromine substitution is crucial for miscibility enhancement in the flame‐retardant brominated PS blends. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1605–1615, 2001

The decomposition of methyl hemiacetals of benzaldehyde in aqueous solution: a study of the effect of aromatic substitution

The acid-base catalysed decomposition of hydrates and hemiacetals of carbonyl compounds are classical examples of reactions where (slow) proton transfer is coupled with heavy atom reorganization, i.e., C—O bond breaking and solvent reorganization. We have studied the influence of m- and p-substitution in the carbonyl electrophile on the kinetics of the acid and base catalysis of the decomposition of methyl hemiacetals of benzaldehyde. The experimental data are well described by three-dimensional More O'Ferrall - Jencks energy contour diagrams according to principles developed by Jencks (the BEMA HAPOTHLE). Thus, for acid catalysis, a Cordes cross-interaction coefficient pxy' = δρ/δpKa = 0.15 indicates the coupled nature of the rate-limiting step in a class e mechanism, similar to conclusions reached from systematic substitution in the nucleophile. Our more extensive set of data for base catalysis permits a more rigorous analysis according to the BEMA HAPOTHLE. The data are consistent with a class n mechanism as also suggested earlier on the basis of substitution in the nucleophile. A slight upward curvature observed in the Hammett plots for the various catalysts is described by the direct correlation parameter py = -δρ/δσ = -0.11. This second derivative demonstrates the concerted nature of the C—O bond cleavage and O-H formation in the transition state, which changes with changing substituent. A class n mechanism for base catalysis is also supported by the observation of a Cordes cross-interaction parameter pxy = -δρ/δpKa = -δβ/δσ = 0.03, which describes the experimentally observed decrease in Hammett ρ with increasing pKa of the catalyst. This change may be rationalized by the movement of a saddle point on a diagonal reaction coordinate in the energy contour diagram, as a resultant of shifts parallel and perpendicular to the coordinate, when the energy along one side of the diagram is changed. It is concluded that observed rate changes as a result of substitution in the electrophile are consistent with and present further confirmation of earlier suggested mechanisms of hemiacetal decomposition reactions.Key words: methyl hemiacetals of benzaldehydes, acid-base catalysed breakdown, Hammett plots, More O'Ferrall - Jencks diagrams.

Structure-localization relationships of 11C-labeled phentermine derivatives: Effect of aromatic substitution

A series of phentermine analogs, including the unsubstituted, the para-F, -Cl, -Br and -I, and the meta-CF 3 derivatives, were labeled by [ 11C]methylation and evaluated in rats to determine the structure-localization relationships for this class of regional cerebral blood flow imaging agents. All the phentermines were well-localized in the brain; however, only the para-substituted agents were well-retained. Localization in the nontarget tissue was affected by the lipophilicity of the substituent. Comparison with the radioiodinated analogs showed virtually identical results, which suggests that the compounds were not significantly metabolized. The agent with the best biodistribution characteristics was the N-[ 11 C] methyl-p- iodophentermine , with the p-bromo analog almost equivalent.

The effect of aromatic substitution on neuroleptic activity in 1-piperazino-3-phenylindans. A comparison based on a new D-2 receptor model with corresponding 10-piperazino-10,11-dihydrodibenzo[b,f]thiepins

The validity of a new dopamine D-2 receptor interaction model based on conformational analysis and least-squares superimposition studies of the indan derivative tefludazine and the thiepin derivative octoclothepin was further tested by comparison of the effect of aromatic substitution on D-2 antagonistic activity in two series of indan and thiepin derivatives. The indan series include new derivatives substituted in the 4-, 7-, 2’- and 3’-position. The substitution effects were largely parallel with one important exception: Only 6-substituted indans have significant neuroleptic activity while both 8- and 7-substituted thiepin derivatives have neuroleptic activity. In indans additional fluorination in the 2’- or 4’-position is demanded to give potent neuroleptic activity, while a 3’-fluoro-substituted derivative was inactive. Fluorination is not necessary in thiepins although 3-fluoro derivatives have a significant prolonged duration of action. Considering the differences in physico-chemical properties, metabolism and pharmacokinetics between the two series, the largely parallel substitution effects support the new D-2 receptor model.

Substituent effects in aromatic substitution of aryltriethyltin compounds by mercuric halides

Second-order rate constants are reported for the reaction of some YC 6H 4SnEt 3 compounds with mercuric halides in tetrahydrofuran, and show that the reaction is one of low selectivity. The substituent effects can be correlated only in terms of Hammett σ-constants, and the data for the meta-methoxy group are anomalous. The results indicate that the rate determining step involves reaction of a π-complex. Activation parameters are reported, and are in accordance with the suggested mechanism.

ChemInform Abstract: INDUCTIVE AND FIELD EFFECTS IN AROMATIC SUBSTITUTION. PART IX. ASSESSMENT OF RESULTS

Chemischer InformationsdienstVolume 7, Issue 16 Preparative Organic Chemistry ChemInform Abstract: INDUCTIVE AND FIELD EFFECTS IN AROMATIC SUBSTITUTION. PART IX. ASSESSMENT OF RESULTS JOHN H. REES, JOHN H. REESSearch for more papers by this authorJOHN H. RIDD, JOHN H. RIDDSearch for more papers by this authorALFREDO RICCI, ALFREDO RICCISearch for more papers by this author JOHN H. REES, JOHN H. REESSearch for more papers by this authorJOHN H. RIDD, JOHN H. RIDDSearch for more papers by this authorALFREDO RICCI, ALFREDO RICCISearch for more papers by this author First published: April 20, 1976 https://doi.org/10.1002/chin.197616083AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue16April 20, 1976 RelatedInformation

Inductive and field effects in aromatic substitution. Part IX. Assessment of results

Earlier work on rates of nitration of the ions Ph[CH2]nX (X = NR3, SR2 PR3, etc.) is analysed in terms of the non-conjugative and conjugative interaction of [CH2]nX with the aromatic ring. Partial rate factors for meta- substitution are taken as a measure of the non-conjugative interaction. The variation of the deactivation at the meta-position with the distance of the pole from the ring is shown to be more consistent with the operation of a field effect than with that of an inductive effect. Apparent exceptions occur when the methylene chain is U shaped for the deactivation is then less than expected. From this and studies with bridged substrates, it is concluded that the transmission of the field effect occurs almost entirely through the molecular cavity but, unlike the inductive effect, is not restricted to the direction of chemical bonds with in that cavity. In the ions Ph[CH2]nX, there is no simple relationship between the orientation of substitution and the deactivation at the meta-position. The additional factor involved is identified as conjugative interaction and an approximate linear free energy relationship is derived relating the para : meta ratio to the σ°R value for the substituent. This relationship is used to provide information on the relative importance of conjugative and non-conjugative interaction, the comparison of nitrogen and phosphorus poles, and the possible effects of the conformation of the CH2NH3 substituent on the deactivation of the ring.

Inductive and field effects in aromatic substitution. Part VII. Hydrogen-isotope exchange in a bridged anthracene derivative carrying a nitrogen pole

The 1H n.m.r. spectra of trans-ll-amino-9, 10-dihydro-12-methyl -9, 10-ethanoanthracene (III) in chloroform solutions containing varying amounts of the shift reagent Eu(dpm)3 show an almost complete separation of the peaks corresponding to the aromatic protons. These peaks have been divided into sets corresponding to the two aromatic rings by spin-decoupling and assigned almost completely by use of the equation for pseudo-contact interactions. This identification has been used to study aromatic hydrogen–deuterium exchange in solutions of (III) in the mixed solvent CF3CO2D–D2SO4–D2O. The extent of exchange has been calculated from the n.m.r. spectra of neutralised samples of the reaction mixture. The kinetic results indicate that reaction occurs through the conjugate acid of (III) and that the NH3 pole deactivates both rings to a similar extent, despite the fact that the distances of the pole from the centres of two rings are very unequal (3.5 and 5.2 Å). Approximate partial rate factors have been calculated for exchange in the conjugate acid of (III).

Inductive and field effects in aromatic substitution. Part VIII. Kinetics of nitration and bromination of the 'onium salts of dithia- and diazacyclophanes

The reactivities, with respect to benzene, of certain open-chain ions (I; X = NMe3 or SMe2) and bridged ions (II; X = NMe2 or SMe) have been compared in nitration and bromination with special reference to the rate retardation caused by bridging [(I)→(II)]. This retardation decreases with an increase in the degree of methylation of the poles and in the length (m) of the methylene chain. For the compounds studied here, the retardation is greater when n= 2 than when n= 1 provided that the length of the bridge and the extent of alkylation of the poles are held constant. The retardation is attributed mainly to the change in the form of the molecular cavity with a further contribution, when n > 1 from the change in the distance of the poles from the aromatic ring.

Inductive and field effects in aromatic substitution. Part VI. The kinetics of hydrogen isotope exchange in quaternary salts of diazacyclophanes and in the related unbridged ions

The kinetics of hydrogen isotope exchange between deuteriosulphuric acid and the aromatic protons of diquaternary ions belonging to the series (I; n= 1–3) and (II; n= 2 or 3) have been studied by n.m.r. spectroscopy. A logarithmic plot of the rates of hydrogen isotope exchange against the rates of the corresponding nitration reactions is linear with a slope of 1·5. This relationship supports the view that steric hindrance is not a major factor in determining the deactivation of the bridged ions (II) relative to the open-chain ions (I) for a given value of n. This deactivation is attributed to the greater field effect of the nitrogen poles in the bridged ions.

Inductive and field effects in aromatic substitution. Part V. Kinetics of nitration of the quaternary salts of diazacyclophanes and of related unbridged ions

The rates of nitration of the open-chain ions (I) in aqueous sulphuric acid are compared with those of the corresponding bridged ions (II). The comparison is used to provide evidence on how the substituent effects of the groups –[CH2]n˙+NR3 depend on the conformation of the carbon chain. The results indicate that for n 2, the deactivation produced by the nitrogen poles depends more directly on the distance of the poles from the centre of the ring than on the number of carbon atoms in the carbon chain. This is interpreted in terms of the field effect of the pole. For n= 1, there is evidence for additional modes of deactivation but the field effect still appears to be the major factor.