C6H4 CH Research Articles

A DFT study of hydride transfers to the carbonyl oxygen of DDQ

Hydride‐transfer reactions between benzylic substrates and 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) were investigated by DFT (density functional theory) calculations. The lowest unoccupied molecular orbital of DDQ has the largest extension on two carbonyl oxygens, which comes from two‐step mixing of antisymmetric orbitals of fragment π MOs. Transition‐state (TS) geometries and activation energies of reactions of four benzylic substrates R2CH2‐para‐C6H4R1 (R1, R2 = H and/or OCH3) with DDQ were calculated. M06‐2X/6‐311(+*)G* was found to be a practical computational method, giving energies and geometries similar to those of M06‐2X/6‐311++G(3df,2pd) and wB97xD/6‐311++G(3df,2pd). For toluene (R1 = R2 = H), an initiation‐propagation model was suggested, and the calculated kinetic isotope effect k(H)/k(D) = 5.0 with the tunnel correction at the propagating step is in good agreement with the experimental value 5.2. A reaction of para‐MeOC6H4CH2(OMe) + DDQ + (H2O)14 → para‐MeOC6H4C(O)H + HOMe + DDQH2 + (H2O)13 was investigated by M06‐2X/6‐311(+*)G*. Four elementary processes were found and the hydride transfer (TS1) is the rate‐determining step. The hydride transfer was promoted by association with the water cluster. The size of the water cluster, (H2O)n, at TS1 was examined. Three models of n = 14, 20, and 26 were found to give similar activation energies. Metal‐free neutral hydride transfers from activated benzylic substrates to DDQ were proposed to be ready processes both kinetically and thermodynamically. © 2015 Wiley Periodicals, Inc.

An Operationally Simple Method for Separating the Rare-Earth Elements Neodymium and Dysprosium.

Rare-earth metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare earths. To incentivize recycling there is a clear need for simple methods for targeted separations of mixtures of rare-earth metal salts. Metal complexes of a tripodal nitroxide ligand [{(2-(t) BuNO)C6 H4 CH2 }3 N](3-) (TriNOx(3-) ), feature a size-sensitive aperture formed of its three η(2) -(N,O) ligand arms. Exposure of metal cations in the aperture induces a self-associative equilibrium comprising [M(TriNOx)thf]/ [M(TriNOx)]2 (M=rare-earth metal). Differences in the equilibrium constants (Keq ) for early and late metals enables simple Nd/Dy separations through leaching with a separation ratio SNd/Dy =359.

Rhodium versus Iridium Catalysts in the Controlled Tandem Hydroformylation–Isomerization of Functionalized Unsaturated Fatty Substrates

AbstractThe hydroformylation of 10‐undecenitrile (1) and related unsaturated fatty substrates (H2CCH(CH2)7CH2R; R=CO2Me, CH2Br, CHO) has been studied with rhodium, iridium, ruthenium, and palladium biphephos catalysts. The reactions proceeded effectively with all four systems, with high selectivities for the linear aldehyde (ratio of linear/branched aldehydes=99:1). The biphephos‐bis[chloro(cyclooctadiene)iridium] system showed a non‐optimized hydroformylation turnover frequency (TOFHF) of 770 h−1 that was only approximately 5 times lower than that of the rhodium‐based system (TOFHF=3320 h−1); the palladium and ruthenium biphephos systems were less active (TOFHF=210 and 310 h−1, respectively). Upon recycling, remarkable productivities were achieved in both cases (TON≈58 000 mol(1/1‐int) mol(Ir)−1 and 250 000 mol(1/1‐int) mol(Rh)−1, in which int=internal olefin). Competitive isomerization of terminal to internal olefins occurred with these catalysts. Iridium biphephos systems allowed slightly better control of the distribution of the internal isomers than the rhodium biphephos catalyst, with higher ratios of 9‐/8‐undecenitrile (1‐int).

B–C Bond Cleavage and Ru–C Bond Formation from a Phosphinoborane: Synthesis of a Bis-σ Borane Aryl-Ruthenium Complex

Compared with the reactivity of o-Ph2P(C6H4–CH2)BH(NiPr2) with [RuH2(η2-H2)2(PCy3)2], the behavior of the phosphinoborane Ph2P(CH2–C6H4)BH(NiPr2) is radically different. No agostic σ-B–H complex could be observed, the reaction leading to the isolation of a new bis-σ borane aryl-ruthenium complex via B–C bond cleavage and Ru–C bond formation. Reactivity studies of this complex with dihydrogen and/or HBArF4 as a proton source enable the formation of a tethered chiral-at-Ru piano-stool cationic complex.

Potentially bioactive organotin(IV) compounds: Synthesis, characterization, in vitro bioactivities and interaction with SS-DNA

Fourteen new organotin(IV) complexes with general formula R2SnL2 or R3SnL where R = CH3, C2H5, C4H9, C6H5, C6H11, CH2–C6H5, C(CH3)3, C8H17 and L = N-[(2-methoxyphenyl)]-4-oxo-4-[oxy]butanamide were synthesized and characterized by elemental analyses, FT-IR, NMR (1H, 13C and 119Sn), mass spectrometry and single crystal X-ray structural analysis. Crystallographic data for four triorganotin(IV) complexes (R3SnL, R = CH3, C2H5, C4H9, CH2–C6H5) showed the tin has approximate trigonal bipyramidal geometry with the R groups in the trigonal plane. The carboxylate groups of ligands L bridge adjacent tin atoms, resulting in polymeric chains. In case of the diorganotin(IV) derivatives a six-coordinate geometry at the tin atom is proposed from spectroscopic evidence. The Me–Sn–Me bond angle in complex 7 was determined from the 2J[119Sn–1H] value as 166.3° that falls in the range of six-coordinate geometry. The ligand and its complexes (1–14) were screened for their antimicrobial, antitumor, cytotoxic and antileishmanial activities and found to be biologically active. The ligand and its complexes bind to DNA via intercalative interactions resulting in hypochromism and minor bathochromic shifts as confirmed by UV–visible spectroscopy. Based on in vitro studies such as the potato disc method, the synthesized compounds were found to possess significant antitumor activity. Also, from cytotoxicity and DNA interaction studies, these compounds can also be used for the prevention and treatment of cancer. Gel electrophoresis assay was used to investigate the damage to double stranded super coiled plasmid pBR322 DNA by the synthesized compounds and compounds 1 and 7 were found to cause the maximum damage. All the synthesized compounds exhibit strong antileishmanial activity that was even higher than that of Amphotericin B, with significant cytotoxicity. This study, therefore, demonstrated the potential use of these compounds as source of novel agents for the treatment of leishmaniasis.

Triorganotin(IV) complexes with o-substituted arylhydroxamates: Synthesis, spectroscopic characterization, X-ray structures and in vitro cytotoxic activities

Six new triorganotin(IV) complexes with six different RN-2-X-benzohydroxamic acid ligands having general formula R′C(O)N(RN)OH (R′ = alkyl/aryl; RN = alkyl/aryl or H), (X = –I, –NO2, –OCH3, –Br and R = –CH3, –C6H5 and –C6H4–CH3), were prepared by condensation method with the respective organotin(IV) chlorides using a stoichiometric ratio of 1:1. The bonding and coordination behaviour of these complexes were investigated on the basis of FT-IR, multinuclear 1H, 13C and 119Sn NMR spectroscopies. Complexes (1) and (3) crystallize in the orthorhombic P2(1)2(1)2(1) space group and complex (2) crystallizes in the triclinic P-1 space group whereas complex (4) crystallizes in the monoclinic P2(1)/c space group. The tested triphenyltin(IV) complexes showed significant cytotoxicities, higher than doxorubicin toward K-562, Jurkat, HepG2 and L929 cells.

Comparative Studies of Thermally Induced Homolytic CarbonCarbon Bond Cleavage Reactions of Strained Dicarba[2]ferrocenophanes and Their Ring-Opened Oligomers and Polymers

Reactivity studies of dicarba[2]ferrocenophanes and also their corresponding ring-opened oligomers and polymers have been conducted in order to provide mechanistic insight into the processes that occur under the conditions of their thermal ring-opening polymerisation (ROP) (300 °C). Thermolysis of dicarba[2]ferrocenophane rac-[Fe(η(5)-C5H4)2(CHPh)2] (rac-14; 300 °C, 1 h) does not lead to thermal ROP. To investigate this system further, rac-14 was heated in the presence of an excess of cyclopentadienyl anion, to mimic the postulated propagating sites for thermally polymerisable analogues. This afforded acyclic [(η(5)-C5H5)Fe(η(5)-C5H4)-CH2Ph] (17) through cleavage of both a Fe-Cp bond and also the C-C bond derived from the dicarba bridge. Evidence supporting a potential homolytic C-C bond cleavage pathway that occurs in the absence of ring-strain was provided through thermolysis of an acyclic analogue of rac-14, namely [(η(5)-C5H5)Fe(η(5)-C5H4)(CHPh)2-C5H5] (15; 300 °C, 1 h), which also afforded ferrocene derivative 17. This reactivity pathway appears general for post-ROP species bearing phenyl substituents on adjacent carbons, and consequently was also observed during the thermolysis of linear polyferrocenylethylene [Fe(η(5)-C5H4)2(CHPh)2]n (16; 300 °C, 1 h), which was prepared by photocontrolled ROP of rac-14 at 5 °C. This afforded ferrocene derivative [Fe(η(5)-C5H4CH2Ph)2] (23) through selective cleavage of the -H(Ph)C-C(Ph)H- bonds in the dicarba linkers. These processes appear to be facilitated by the presence of bulky, radical-stabilising phenyl substituents on each carbon of the linker, as demonstrated through the contrasting thermal properties of unsubstituted linear trimer [(η(5)-C5H5)Fe(η(5)-C5H4)(CH2)2(η(5)-C5H4)Fe(η(5)-C5H4)(CH2)2(η(5)-C5H4)Fe(η(5)-C5H5)] (29) with a -H2 C-CH2- spacer, which proved significantly more stable under analogous conditions. Evidence for the radical intermediates formed through C-C bond cleavage was detected through high-resolution mass spectrometric analysis of co-thermolysis reactions involving rac-14 and 15 (300 °C, 1 h), which indicated the presence of higher molecular weight species, postulated to be formed through cross-coupling of these intermediates.

A pyridyl–carboxylate type linking ligand containing an intervening amide group and its cadmium and nickel coordination polymers: (3-py)–C(O)NH–C6H4–CH2–COOH (HL), {[CdL2](H2O)}∞, and {[NiL2(H2O)2](H2O)}∞

A new pyridyl–carboxylate type linking ligand with an intervening amide group, (3-py)–C(O)NH–C6H4–CH2–COOH (HL), was prepared from 4-aminophenylacetic acid and nicotinoyl chloride hydrochloride. By employing this ligand, two coordination polymers were prepared under hydrothermal conditions: {[CdL2](H2O)}∞ (1) and {[NiL2(H2O)2](H2O)}∞ (2). The ligand exhibits distinct coordination modes in polymers 1 and 2. These bonding modes result in the different topologies: a 2-D layer for polymer 1 and a 1-D double-chain for polymer 2. In the case of polymer 2, several types of hydrogen bonds connect the 1-D polymers to a 2-D network.

Temperature dependences for the reactions of Ar+, O2+, and C7H7+ with toluene and ethylbenzene

We have studied the reactions of Ar+, O2+, and C7H7+ with toluene (CH3–C6H5) and ethylbenzene (C2H5–C6H5) as a function of temperature. Ar+ reacts with C7H8 at the collision rate constant at both 300 and 500K to produce mainly C7H7+ cations (∼85%), with the remainder of the reactivity divided into numerous small channels. The fraction of C7H7+ produced as benzylium+ (6 membered ring, Bz+) as opposed to tropylium+ (7 membered ring, Tr+) is determined through ion-molecule reactivity to be primarily Bz+. The reaction of Ar+ with C8H10 proceeds at slightly lower than the collision rate constant at 300K, but increases to the collision rate constant at 500K. Over 80% of the products were C7H7+, the large majority of which also is Bz+. The O2+ reaction with C8H10 proceeds at the collision rate constant and produces C8H10+, C6H6+, and C7H7+, with the latter again primarily being Bz+. C7H7+ was found to react with both CH3–C6H5 and C2H5–C6H5 by both collisionally stabilized clustering and a bimolecular reaction forming R–C6H4–CH2+. At 300K the rate constants are about half of the collision rate constant and drop rapidly with temperature. About 2/3 of the products are clusters at 300K, 1/3 at 400K, and negligible amounts at 500 and 600K. Evidence for thermal dissociation of the cluster is presented. Calculations show the most stable structure is the one where the methylene group of benzylium is coordinated at the para position of the alkylbenzene, with one phenyl group approximately 45° out of plane relative to the other. A bond strength of 15–16kcalmol−1 is calculated for both neutrals. Numerous less stable structures were found.

Lanthanide(III) 1,4-Phenylenediacetate Complexes: The Relation Between the Structure and Thermal Properties

The series of isostructural lanthanide coordination polymers with the empirical formula [Ln2(PDA)3(H2O)]·2H2O, where PDA = 1,4-phenylenediacetate anion = [C8H8(COO)2]2−; Ln = La-Lu(III), and Y(III) were produced in the reaction of LnCl3·nH2O with ammonium salt of 1,4-phenylenediacetic acid in water solution. The compounds were characterised structurally using powder X-ray diffraction, elemental and thermogravimetric analyses as well as FT-IR spectroscopy. Thermogravimetric analyses show that in the range 60–170 °C the dehydration process occurs. The thermal stability of dehydrated compounds, Ln2(PDA)3 increased from about 200–350 °C in the whole series of complexes. Single-crystal X-ray diffraction analysis for the Gd(III) complex revealed that the compound crystallizes in the monoclinic P21/c space group with a = 21.863(2) A, b = 10.035(1) A, c = 13.854(1) A, β = 91.53(1)° and V = 3,038.5(4) A3. The complex contains one-dimensional gadolinium-carboxylato chains, which are connected with the –CH2–C6H4–CH2– spacers of PDA ligand to the three-dimensional metal–organic framework.

Structural variation, π-charge transfer, and transmission of electronic substituent effects in (E)-β-substituted styrenes: a quantum chemical study

The nature and transmission mechanism of substituent effects in (E)-β-substituted styrenes, C6H5–CH=CH–X, have been investigated from the structural changes induced by a variable substituent on the phenyl group. The molecular structures of 46 (E)-β-substituted styrenes were determined from MO calculations at the B3LYP/6-311++G** level of theory. The structural variation of the phenyl probe is best represented by two orthogonal linear combinations of the internal ring angles, S F STY and S R STY . Regression analysis of S F STY using appropriate explanatory variables reveals a composite field effect, the main component of which originates from the long-range effect of the substituent enhanced by field-induced π-polarization of the vinylene spacer and resonance-induced field effects. The electronegativity of the substituent also plays a role in determining the value of S F STY . Comparison with coplanar 4-substituted biphenyls reveals that the components of the field effect in the two molecular systems are of the same nature (apart from the electronegativity contribution, which is not present in biphenyl derivatives). However, the structural variation of the phenyl probe is more pronounced in (E)-β-substituted styrenes due to the shorter distance between substituent and probe. Analysis of π-charge distribution shows that the aptitude of the substituents to exchange π-electrons with the styrene and coplanar biphenyl frames is nearly the same. Nevertheless, the π-charge variation on the phenyl probe of (E)-β-substituted styrenes is 57 % greater than the corresponding quantity in coplanar 4-substituted biphenyls. Thus, the vinylene spacer is more effective than the phenylene spacer in transmitting π-charges. The S R STY parameter is related to the amount of π-charge transferred from the –CH=CH–X moiety into the π-system of the benzene ring, or vice versa, due to the resonance effect of the variable substituent and, to a lesser extent, to field-induced π-polarization.

Synthesis and structural characterization of some binuclear acetylacetone and Schiff’s base complexes containing aluminum(III) atoms in different coordination states

Some Schiff’s base complexes of aluminum(III) of the type (CH3COCHCOCH3)2Al(µ-OPri)2AlLn(OPri)2-n [where LH=OHC(R)=CHC(R′)=NC6H5; R=R′=CH3,C6H5; R=CH3, R′=C6H5; LH=C6H4(OH)CH=NC6H5 and n=1 or 2] were prepared and characterized by various spectroscopic techniques. The molecular weight measurements indicated their binuclear nature. The 27Al nuclear magnetic resonance spectra of representative compounds [(CH3COCHCOCH3)2Al(µ-OPri)2Al{OC(C6H5)=CHC(C6H5)=NC6H5}(OPri)] [3] and [(CH3COCHCOCH3)2 Al(µ-OPri)2Al{OC(CH3)=CHC(CH3)=NC6H5}2] [6] suggest the presence of aluminum(III) atoms in different coordination states.

MM quadruple bonds supported by cyanoacrylate ligands. Extending photon harvesting into the near infrared and studies of the MLCT states

The compounds trans-M2(TiPB)2(L)2 and trans-M2(TiPB)2(L′)2 have been prepared from the reactions between M2(TiPB)4 (TiPB = 2,4,6-triisopropylbenzoate, M = Mo or W) and LH or L′H (∼2 equiv.), respectively, where L = O2CC(CN)CH–C6H4–NPh2 and L′ = O2CC(CN)CH–C4H3S–C6H4–NPh2. These cyanoacrylate ligands promote intense M2δ to L or L′ π*-transitions that span the range 550–1100 nm. The two molybdenum complexes have been characterized by single crystal X-ray studies that reveal the extensive L–M2222–L or L′–M2222–L′ M2δ–ligand π-conjugation. The new compounds have been characterized by electronic structure calculations employing density functional theory (DFT) and time-dependent-DFT, cyclic voltammetry, electronic absorption and steady state emission spectroscopy and femtosecond (fs) and nanosecond (ns) time resolved transient absorption (TA) and fs time-resolved infrared spectroscopy (TRIR). The latter allows the determination of the S1 states as 1MLCT that are delocalized over both L and L′. For molybdenum the T1 states are 3MoMoδδ* whereas for tungsten they are 3MLCT.

Electrochemical Properties and Regioselectivity of Cyclopalladation of Chiral Ferrocenylimines Deriving from (S)-Ferrocenylethylamine

Treatment of a cyclopalladated complex derived from chiral ferrocenylimine (η5-C5H5)Fe(η5-C5H4)–CH(CH3)–N=CH–2-C4H3S, (Sc)-1, with PPh3 produced the heteroannular palladacycle (Sc)-3 in which palladation occurred at the unsubstituted cyclopentadiene ring. While for (η5-C5H5)Fe(η5-C5H4)–CH(CH3)–N=CH–C6H5, (Sc)-4, cyclopalladation took place mainly at the phenyl ring; the heteroannular palladacycle (Sc)-6, as a minor product, was also obtained. Single crystal X-ray analysis, electrochemical, and computational studies have been performed, showing good agreement with experimental results.

New hyperbranched carbosiloxane–carbosilane polymers with aromatic units in the backbone

New hyperbranched polymers based on a carbosiloxane–carbosilane skeleton with aromatic units in the backbone have been prepared via one-pot hydrosilylation reaction using HSi(Me)2–O–CH2–C6H4–OSiMe–(CH2)4(C3H5)2 as a novel AB2 monomer. These polymers are easy to prepare, have narrow polydispersity values and present allyl groups on the surface which can be used as synthetic platforms for the introduction of different terminal groups like amine groups through hydrosilylation reactions, opening the door to functionalized polymers. The polymerization process was monitored using real-time 1H NMR spectroscopy and the resulting hyperbranched polymers were characterized using 1H NMR, 13C NMR, 29Si NMR and SEC/MALLS. The degree of branching in these polymers was determined by quantitative 29Si NMR spectroscopy and found to be very close to the theoretical value of 0.50 for AB2 systems. The hydrolytic degradation of these polymers in protic solvents has been studied by 29Si NMR.

Altering the Static Dipole on Surfaces through Chemistry: Molecular Films of Zwitterionic Quinonoids

The adsorption of molecular films made of small molecules with a large intrinsic electrical dipole has been explored. The data indicate that such dipolar molecules may be used for altering the interface dipole screening at the metal electrode interface in organic electronics. More specifically, we have investigated the surface electronic spectroscopic properties of zwitterionic molecules containing 12π electrons of the p-benzoquinonemonoimine type, C(6)H(2)(···NHR)(2)(···O)(2)(R = H (1), n-C(4)H(9) (2), C(3)H(6)-S-CH(3) (3), C(3)H(6)-O-CH(3) (4), CH(2)-C(6)H(5) (5)), adsorbed on Au. These molecules are stable zwitterions by virtue of the meta positions occupied by the nitrogen and oxygen substituents on the central ring, respectively. The structures of 2-4 have been determined by single crystal X-ray diffraction and indicate that in these molecules, two chemically connected but electronically not conjugated 6π electron subunits are present, which explains their strong dipolar character. We systematically observed that homogeneous molecular films with thickness as small as 1 nm were formed on Au, which fully cover the surface, even for a variety of R substituents. Preferential adsorption toward the patterned gold areas on SiO(2) substrates was found with 4. Optimum self-assembling of 2 and 5 results in ordered close packed films, which exhibit n-type character, based on the position of the Fermi level close to the conduction band minimum, suggesting high conductivity properties. This new type of self-assembled molecular films offers interesting possibilities for engineering metal-organic interfaces, of critical importance for organic electronics.

Activation of - N=CH - bond in a Schiff base by divalent nickel monitored by NMR evidence

The Schiff base, 2-salicylidene-4-aminophenyl benzimidazole in ethanol undergoes activation of -N=CH- bond by Ni(2+) in the presence of ammonia or primary alkyl amine to produce nickel complexes of the formula Ni{o-C(6)H(4)(O)CH NR}(2) . n H(2)O [R = H, Me; n = 0; R = Et, n = 0.5] and 4-aminophenyl benzimidazole. The products have been identified by elemental analysis, magnetic susceptibility measurements and IR, ESR, mass and extensive NMR spectral studies. The possible mechanism for the activation of -N=CH- bond has also been proposed.

Carboxylation of Toluene by CO2Generatingp-Toluic Acid: A Kinetic Look

A kinetic study involving stoichiometry, order of reaction, rate constants (k), and rate laws has been performed on carboxylation of toluene by CO2 generating p-toluic acid by two routes: (a) Friedel–Crafts reaction, C6H5–CH3 + CO2 + Al2Cl6 → CH3–C6H4–COOAl2Cl5 + HCl and (b) Friedel–Crafts reaction with incubation method involving two steps, CO2 + Al2Cl6 → CO2:Al2Cl6 and CO2:Al2Cl6 + C6H5–CH3 → CH3–C6H4–COOAl2Cl5 + HCl. The adduct OCO:Al2Cl6 was estimated by monitoring the peak at 1662 cm–1 in the FTIR spectra. The k values for the Friedel–Crafts reaction was found to be 2.28 × 10–9 mol–2 h–1, which is much lower than that for the reactions involved in the incubation method, viz., 5.4 × 10–5 and 1.9 × 10–3 mol–1 h–1, respectively. ΔE, ΔG, ΔS, ΔH, and the Arrhenius constant (A) have been calculated for the above reactions. Comparison shows that the incubation method is faster than the Friedel–Crafts reaction. However, both the reactions follow first order kinetics with respect to each of the reactants.

Orthorhombic Polymorphs of 1-Phenyl-3-(3-Hydroxyphenyl)-2-Propen-1-One

Chalcones, 1,3-diphenyl-2-propene-1-ones, exist naturally and synthetically, and are characterized by the linkage of two aromatic rings joining a three carbon α-β-unsaturated carbonyl entity. We report the observation of two new polymorphs of a hydroxy chalcone, C6H5–CO–CH=CH–C6H4 (m-OH), identified as a result of a Claisen–Schmidt synthesis and manual screening technique. One polymorph of this compound has been reported previously and exists in the monoclinic system, space group P2/n, with unit cell parameters a = 13.295(6) A, b = 5.659(2) A, c = 16.144(8) A, β = 109.73(5)°, V = 1143.3(9) A3, and Z = 4. Two crystalline forms (II and III) reported herein, are polymorphs of the reported monoclinic form (I). Form II exists in the orthorhombic system, space group Pca21, with unit cell constants a = 11.631 (2) A, b = 13.163 (3) A, c = 7.3977 (14) A, V = 1132.6 (4) A3, and Z = 4. Form III also crystallizes in the orthorhombic system, however in space group Pbca, with unit cell parameters a = 11.8100(8) A, b = 7.4075(5) A, c = 25.8729(19) A, V = 2263.4(3) A3, and Z = 8. Variations in the hydrogen bonding connectivity help to distinguish these two forms from the monoclinic, whereas crystal packing differentiates the two orthorhombic forms. The conformation of the C=C (C2–C3) is E for both orthorhombic forms. We report the crystal structures of two polymorphic modifications of a hydroxy chalcone, C6H5–CO–CH = CH–C6H4 (m-OH). Molecular structure of C6H5–CO–CH = CH–C6H4 (m-OH) with atomic numbering scheme of forms II and III .

Differentiation of Diasteromeric α-Sulfanyl-β-Amino Acid Derivatives by Electrospray Ionisation Tandem Mass Spectrometry

A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.