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Substituent Constants (substituent + constant)

Distribution by Scientific Domains
Chemistry100%

Kinds of Substituent Constants

  • hammett substituent constant
    		•

    Selected Abstracts

    Synthesis and nuclear magnetic resonance spectroscopic studies of 1-arylpyrroles

    JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2000
    Chang Kiu Lee
    A series of m - and p -substituted 1-phenyl, 1-benzyl, 1-benzoyl, and 1-(2-phenylethyl)pyrroles was prepared and their 1H and 13C nmr spectroscopic characteristics were examined. In general, good correlations were observed between the chemical shift values of the ,H and the ,C of pyrroles [except 1-(2-phenylethyl)pyrroles] and the Hammettt ,. The observation may be explained in terms of the electronic effects of the substituents which are transmitted through bonds and through space by interaction of the p orbitals between ,Cs of the pyrrole ring and m - and pCs of the phenyl ring. Substituent constants of 1-pyrrolyl, 1-pyrrolylmethyl, and 1-pyrroloyl groups for the 1H and 13C chemical shifts of phenyl ring are also presented. [source]

    Reaction of 4-benzylidene-2-methyl-5-oxazolone with amines, Part 2: Influence of substituents in para-position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kinetics

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002
    B. Bet, akowska
    An influence of a structure of the amine (benzylamine, N -methyl-benzylamine, N -isopropyl-benzylamine, N -methyl-butylamine, N -ethyl-butylamine, sec -butylamine, and tert -butylamine) on a rate constant of the ring-opening reaction of 4-benzylidene-2-methyl-5-oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant , as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring-opening reaction was studied. The substituents (OH, OCH3, N(CH3)2, Cl, NO2) in para-position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring-opening reaction decreased with increase of the electron-donating properties of the substituent. A good correlation between the rate constants of the reaction of 4-(4,-substituted-benzylidene)-2-methyl-5-oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148,155, 2002; DOI 10.1002/kin.10039 [source]

    Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acid

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2006
    Vilve Nummert
    Abstract Infrared spectra of 25 substituted phenyl esters of benzoic acid C6H5CO2C6H4 -X (XH, 3-Cl, 3-F, 3-CN, 3-NO2, 3-CH3, 3-OH, 3-NH2, 4-Cl, 4-F, 4-NO2, 4-CN, 4-OCH3, 4-CH3, 4-NH2, 2-Cl, 2-F, 2-I, 2-NO2, 2-CF3, 2-CN, 2-CH3, 2-OCH3, 2-N(CH3)2, 2-C(CH3)3), 8 alkyl benzoates C6H5CO2R (XCH3, CH2CH3, CH2Cl, CH2CN, CH2CCH, CH2CH2Cl, CH2CH2OCH3, CH2C6H5), and 22 phenyl esters of substituted benzoic acids X-C6H4CO2C6H5 (X3-Cl, 3-NO2, 3-CH3, 3-N(CH3)2, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-C(CH3)3, 4-OCH3, 4-NH2, 2-Cl, 2-F, 2-Br, 2-I, 2-NO2, 2-CN, 2-CF3, 2-CH3, 2-OCH3, 2-NH2) were recorded in tetrachloromethane in the region of 400,4000,cm,1. Carbonyl stretching frequencies ,CO for meta - and para -substituted phenyl esters of benzoic acid and phenyl esters of meta -substituted benzoic acids were shown to correlate with the substituent constants ,o. The influence of the through resonance effect on ,CO was found to be important in the case of +Rpara substituents in the benzoyl part of phenyl benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate with the inductive substituent constant ,I only. In the benzoyl part of the esters the carbonyl stretching frequencies of cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter equations: (,CO)cis,=,(,CO)o,+,c1,I,+,c3,and (,CO)trans,=,(,CO)o,+,c1,p+,+,c3, (R,=,0.99). The trans isomers of phenyl esters of ortho -substituted benzoic acids showed direct resonance similar to that for para derivatives. The positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition of resonance between the phenyl ring and the carboxy-group caused by bulky ortho substituents. The existence of cis/trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at B3LYP/6-311+G** level for the ortho -substituted benzoates. In the case of alkyl benzoates good correlations of ,CO values were obtained when both the Taft ,* and the steric constants were used. For meta - and para -substituted phenyl benzoates s - trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular relative to the carbonyl bond plane was supported. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Solvatochromism of carbenium,arene EDA (electrondonor,acceptor) complexes and their behaviour on silica

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2001
    Stefan Spange
    Abstract Spectral characteristics of two different types of electron donor,acceptor (EDA) complexes with charged components (arene,carbenium and anion,, acceptor) are presented. The UV,Vis absorption maxima of the charge-transfer (CT) band (,max,CT) of the EDA complexes were measured in various solvents and after adsorption on silica. Tropylium, triarylmethylium and diarylmethylium ions in combination with aromatic , donors, e.g. pyrene, acenaphthene and methoxy-substituted benzene derivatives and also the tetraethylammonium iodide,1,3,5-trinitrobenzene complex have been investigated by means of a special UV,Vis technique in transparent slurries of silica nanoparticles in 1,2-dichloroethane. Multiple linear regression analyses of the ,max,CT values of the EDA complexes in various solvents and on silica with the Kamlet,Taft solvent parameters and structure,reactivity terms of the complex components, e.g. the oxidation potential of the arene component or the Hammett substituent constant, ,p+, of the arylmethyl component, show their related properties to the solution complexes. The influence of the electron-pair donating capacity of a solvent on ,max,CT of carbenium/arene complexes was compared with the property of the silica surface in order to link EDA complexes. For the diarylmethyl carbenium ion,pyrene complexes on silica, the presence of a ,-like structure is discussed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Molecular Connectivity: Polarity Correction to Improve Correlation with Hydrophobicity

    MOLECULAR INFORMATICS, Issue 2-3 2004

    Abstract Contrary to belief in some quarters, molecular connectivites correlate only very poorly with hydrophobicity. We have devised a simple polarity correction to the calculation of first-order molecular connectivity (1,), which involves subtracting, instead of adding, the bond contributions (, values) for bonds between atoms i and j where j is a heteroatom other than halogen, to give a 1,p value. For a set of 23 diverse substituents, the correlation between 1, and , (the hydrophobic substituent constant) yielded r2=0.123, whilst that between 1,p and , yielded r2=0.771. When the method was applied to the correlation of the protein-binding constants for a set of 42 diverse compounds with 1,, r2 improved from 0.078 to 0.443., [source]

    Ortho Effects in Quantitative Structure Activity Relationships for Lipase Inhibition by Aryl Carbamates

    MOLECULAR INFORMATICS, Issue 8 2003
    Gialih Lin
    Abstract Ortho -substituted phenyl- N -butyl carbamates (1,11) are synthesized and evaluated for their inhibition effects on Pseudomonas species lipase. Carbamates 1,11 are characterized as pseudo-substrate inhibitors of the enzyme. The logarithms of dissociation constant (Ki), carbamylation constant (k2), and bimolecular inhibition constant (ki) multiply linearly correlate with Hammett substituent constant (,), Taft-Kutter-Hansch ortho steric constant (ES), and Swan-Lupton field constant (F). For ,logKi -, logk2 -, and logki -correlations, values of ,, ,, f, ,XR are 0.2, ,0.06, ,1.7, 0.8; 0.0, 0.0, 1.0, ,0.07; and ,1.8, 7, 0.6, 5; respectively. The enzyme inhibition mechanism is composed of four steps: 1) the first step which is protonation of carbamates 1,11, 2) the second step (Ki1) which involves in the proton 1,3-shift of protonated carbamates 1,11 then the pseudo- trans to cis conformational change, 3) the third step (Ki2) which is formation of a negative charged enzyme-inhibitor tetrahedral intermediate, and 4) the fourth step (k2) which is the carbamylation step. The former three steps are likely composed of the Ki step. There is little ortho steric enhancement effect in the Ki step. From cross-interaction correlations, distance between carbamate and phenyl substituents in transition state for the Ki step is relatively short due to a large ,XR value of 7. The k2 step is insensitive to ortho steric effect. The k2 step involves in departure of leaving group, substituted phenol in which is protonated from the proton 1,3-shift but not from the active site histidine of the enzyme. From cross-interaction correlations, the distance between carbamate and phenyl substituents in transition state for the k2 step is relatively long due to a small ,XR value of 0.6. [source]

    Correlation analysis of reactivity in the oxidation of anilines by nicotinium dichromate in nonaqueous media

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2006
    D. S. Bhuvaneshwari
    The kinetics of oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate (NDC) in different organic solvent media in the presence of p -toluenesulfonic acid (TsOH) has been investigated. The rate of the reaction is zero order with respect to substrate, first order in NDC, and is found to increase with increase in [TsOH]. The various thermodynamic parameters for the oxidation have been reported and discussed along with the validity of the isokinetic relationship. The specific rate of oxidizing species-anilines reaction (k2) correlates with Hammett's substituent constants affording negative reaction constants. The effect of para- and meta-substituents on the oxidation rates confirms to Swain et al.'s substituent constants F and R, both with negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and E while showing satisfactory correlation with Kamlet,Taft's solvatochromic parameters (,, ,, and ,*). © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 657,665, 2006 [source]

    Studies on the kinetics of imidazolium fluorochromate oxidation of some meta - and para -substituted anilines in nonaqueous media

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2006
    D. S. Bhuvaneshwari
    The imidazolium fluorochromate (IFC) oxidation of meta - and para -substituted anilines, in seven organic solvents, in the presence of p -toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta - and para -substituted anilines at 299,322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species-anilines reaction (k2) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ,r and ENT. A correlation of rate data with Kamlet,Taft solvatochromic parameters (,, ,, ,*) suggests that the specific solute,solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute,solvent complexation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166,175, 2006 [source]

    Reaction of 4-benzylidene-2-methyl-5-oxazolone with amines, Part 2: Influence of substituents in para-position in the phenyl ring and a substituent on amine nitrogen atom on the reaction kinetics

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2002
    B. Bet, akowska
    An influence of a structure of the amine (benzylamine, N -methyl-benzylamine, N -isopropyl-benzylamine, N -methyl-butylamine, N -ethyl-butylamine, sec -butylamine, and tert -butylamine) on a rate constant of the ring-opening reaction of 4-benzylidene-2-methyl-5-oxazolone (Ox) was studied. The good correlation between logarithm of the rate constants and Charton's steric substituent constant , as well as good correlation with a form of the simple branching equation indicate that there is a steric effect because of substitution at C1 carbon atom of nucleophile which decreases the reaction rate. Additionally, an influence of a structure of the benzylidene moiety of Ox on a rate of the oxazolone ring-opening reaction was studied. The substituents (OH, OCH3, N(CH3)2, Cl, NO2) in para-position of the phenyl ring of Ox substantially modified the rate of the reaction with benzylamine in acetonitrile. The rate of the Ox ring-opening reaction decreased with increase of the electron-donating properties of the substituent. A good correlation between the rate constants of the reaction of 4-(4,-substituted-benzylidene)-2-methyl-5-oxazolones with benzylamine and the electron density at the reaction center (carbon C5 of the oxazolone ring), calculated using ab initio method, and the Hammett substituent constants, and CR equation were established. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 148,155, 2002; DOI 10.1002/kin.10039 [source]

    A generalized exo -anomeric effect.

    ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2000
    Substituent, solvent effects on the conformational equilibria of 2-(arylseleno)cyclohexanones
    The effects of substitution and solvent on the conformational equilibria of 2-[(4-R-substituted-phenyl)seleno]cyclohexanones are described. The conformational equilibria were determined by comparison of the linewidths of the H-2 resonances in the 1H NMR spectra of the conformationally averaged systems with those of the anancomeric (highly biased) 4-isopropyl-2-substituted cyclohexanones. The substituent (R = NMe2, OMe, Me, H, F, Cl, CF3, NO2) and solvent ((CD3)2CO, CD3CN, CD2Cl2, CDCl3) effects are discussed in terms of electrostatic effects and the possible stabilizing orbital interactions. The values of Keq (axial-equatorial) increase as the substituent becomes more electron withdrawing, in agreement with the dominance of nSe , ,*C=O or ,C-Se , ,*C=O orbital interactions in the axial conformers. The increase in the proportion of the equatorial isomers in more polar solvents for a given substituent suggests a damping of the dipolar interactions in the equatorial isomers. However, the proportion of the equatorial isomers in a given solvent increases as the substituent becomes more electron withdrawing, indicating that electrostatic interactions do not dominate in controlling the conformational equilibria. Analysis of the equilibrium data by means of a dual substituent parameter approach indicates the best correlation with ,I and ,+R substituent constants in CD2Cl2 and with ,I and ,°R substituent constants in CD3CN, with similar sensitivities to the resonance and polar effects. The correlations are interpreted in terms of accommodation of effective positive charge on the selenium atom in the axial isomers in CD2Cl2, and a lesser sensitivity to the buildup of positive charge in the more polar solvent CD3CN. Comparison of the IR ,CO -stretching frequencies for the axial and equatorial ArSe-substituted anancomeric systems (R = NO2, NMe2) indicates a higher stretching frequency for the NO2 -substituted isomers. In the case of the NMe2 -substituted compounds, ,CO appears at a higher frequency in the equatorial isomer, whereas in the case of the NO2 -substituted compounds, ,CO is less sensitive to the axial or equatorial orientation of the substituent. The results are consistent with the operation of nse , ,*c=0 or ,C-Se , ,*C=O orbital interactions in the axial isomers. The JC2-H2 values in the axially-substituted anancomeric isomers are of greater magnitude than those in the equatorially-substituted isomers, which is also consistent with the operation of the orbital interactions described above. There is, however, no marked substituent effect on the JC2,H2 values within the series of axial or equatorial isomers. We argue that this does not support the dominance of ,C-Se , ,*C=O orbital interactions. Examination of crystal structures reported in the literature for related compounds indicates a particular gauche orientation about the C2,Se bond, which lends further support to the operation of an nSe , ,*C=O orbital interaction. We suggest that the latter interaction is a manifestation of a generalized exo -anomeric effect. [source]

    Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acid

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2006
    Vilve Nummert
    Abstract Infrared spectra of 25 substituted phenyl esters of benzoic acid C6H5CO2C6H4 -X (XH, 3-Cl, 3-F, 3-CN, 3-NO2, 3-CH3, 3-OH, 3-NH2, 4-Cl, 4-F, 4-NO2, 4-CN, 4-OCH3, 4-CH3, 4-NH2, 2-Cl, 2-F, 2-I, 2-NO2, 2-CF3, 2-CN, 2-CH3, 2-OCH3, 2-N(CH3)2, 2-C(CH3)3), 8 alkyl benzoates C6H5CO2R (XCH3, CH2CH3, CH2Cl, CH2CN, CH2CCH, CH2CH2Cl, CH2CH2OCH3, CH2C6H5), and 22 phenyl esters of substituted benzoic acids X-C6H4CO2C6H5 (X3-Cl, 3-NO2, 3-CH3, 3-N(CH3)2, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-C(CH3)3, 4-OCH3, 4-NH2, 2-Cl, 2-F, 2-Br, 2-I, 2-NO2, 2-CN, 2-CF3, 2-CH3, 2-OCH3, 2-NH2) were recorded in tetrachloromethane in the region of 400,4000,cm,1. Carbonyl stretching frequencies ,CO for meta - and para -substituted phenyl esters of benzoic acid and phenyl esters of meta -substituted benzoic acids were shown to correlate with the substituent constants ,o. The influence of the through resonance effect on ,CO was found to be important in the case of +Rpara substituents in the benzoyl part of phenyl benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate with the inductive substituent constant ,I only. In the benzoyl part of the esters the carbonyl stretching frequencies of cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter equations: (,CO)cis,=,(,CO)o,+,c1,I,+,c3,and (,CO)trans,=,(,CO)o,+,c1,p+,+,c3, (R,=,0.99). The trans isomers of phenyl esters of ortho -substituted benzoic acids showed direct resonance similar to that for para derivatives. The positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition of resonance between the phenyl ring and the carboxy-group caused by bulky ortho substituents. The existence of cis/trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at B3LYP/6-311+G** level for the ortho -substituted benzoates. In the case of alkyl benzoates good correlations of ,CO values were obtained when both the Taft ,* and the steric constants were used. For meta - and para -substituted phenyl benzoates s - trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular relative to the carbonyl bond plane was supported. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Infrared intensities of benzene derivatives as a measure of the substituent resonance effect

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2001
    Karel Palát Jr
    Abstract Infrared spectra of 39 benzene mono-derivatives were recorded in the region 1000,1800,cm,1 and the intensities of the bands ,16a and ,16b were determined by computer separation. The intensities correlated with the squared resonance substituent constants ,Ro as found by Katritzky and co-workers, but band separation does not represent any essential improvement compared with the earlier simpler technique. With substituents including an NH2 group, there is still an interference with the NH2 scissoring deformation band: in these cases deuteration is more effective than band separation. Several new constants ,Ro were determined spectroscopically for substituents of interest in pharmacology and these constants were also calculated by a quantum chemical model. The latter procedure seems to be most efficient and reasonably reliable for calculating new ,Ro constants; the only problem may be with the conformation in the case of axially unsymmetrical substituents. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    15N NMR chemical shifts of ring substituted benzonitriles

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2006

    Abstract 15N chemical shifts in an extensive series of para (15) and meta (15) as well as ortho (8) substituted benzonitriles, XC6H4CN, were measured in deuteriochloroform solutions, using three different methods of referencing. The standard error of the average chemical shift was less than 0.03 ppm in most cases. The results are discussed for both empirical correlations with substituent parameters and quantum chemical calculations. The 15N chemical shifts calculated at the GIAO/B3LYP/6,31 + G*//B3LYP/6,31 + G* level reproduce the experimental values well, and include nitrogen atoms in the substituent groups (range of 300 ppm with slope 0.98 and R = 0.998, n = 43). The 15N shifts in hydroxybenzonitriles are affected by interaction with the OH group. Therefore, these derivatives are excluded from the correlation analysis. The resultant 15N chemical shift correlates well with substituent constants, both in the simple Hammett or DSP relationships and the 13C substituent-induced chemical shifts of the CN carbon. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Computation and analysis of 19F substituent chemical shifts of some bridgehead-substituted polycyclic alkyl fluorides

    MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003
    William Adcock
    Abstract The 19F NMR shieldings for several remotely substituted rigid polycyclic alkyl fluorides with common sets of substituents covering a wide range of electronic effects were calculated using the DFT-GIAO theoretical model. The level of theory, B3LYP/6,311+G(2d,p), was chosen based on trial calculations which gave good agreement with experimental values where known. The optimized geometries were used to obtain various molecular parameters (fluorine natural charges, electron occupancies on fluorine of lone pairs and of the CF bond, and hybridization states) by means of natural bond orbital (NBO) analysis which could help in understanding electronic transmission mechanisms underlying 19F substituent chemical shifts (SCS) in these systems. Linear regression analysis was employed to explore the relationship between the calculated 19F SCS and polar substituent constants and also the NBO derived molecular parameters. The 19F SCS are best described by an electronegativity parameter. The most pertinent molecular parameters appear to be the occupation number of the NBO p-type fluorine lone pair and the occupation number of the CF antibonding orbital. This trend suggests that in these types of rigid saturated systems hyperconjugative interactions play a key role in determining the 19F SCS. Electrostatic field effects appear to be relatively unimportant. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Gas-phase basicities of polyfunctional molecules.

    MASS SPECTROMETRY REVIEWS, Issue 6 2007
    Part 1: Theory, methods
    Abstract The experimental and theoretical methods of determination of gas-phase basicities, proton affinities and protonation entropies are presented in a tutorial form. Particularities and limitations of these methods when applied to polyfunctional molecules are emphasized. Structural effects during the protonation process in the gas-phase and their consequences on the corresponding thermochemistry are reviewed and classified. The role of the nature of the basic site (protonation on non-bonded electron pairs or on ,-electron systems) and of substituent effects (electrostatic and resonance) are first examined. Then, linear correlations observed between gas-phase basicities and ionization energies or substituent constants are recalled. Hydrogen bonding plays a special part in proton transfer reactions and in the protonation characteristics of polyfunctional molecules. A survey of the main properties of intermolecular and intramolecular hydrogen bonding in both neutral and protonated species is proposed. Consequences on the protonation thermochemistry, particularly of polyfunctional molecules are discussed. Finally, chemical reactions which may potentially occur inside protonated clusters during the measurement of gas-phase basicities or inside a protonated polyfunctional molecule is examined. Examples of bond dissociations with hydride or alkyl migrations, proton transport catalysis, tautomerization, cyclization, ring opening and nucleophilic substitution are presented to illustrate the potentially complex chemistry that may accompany the protonation of polyfunctional molecules. © 2007 Wiley Periodicals, Inc., Mass Spec Rev 26:775,835, 2007 [source]

    Study of fragmentation pathways of lithiated ,,, -unsaturated thioesters by electrospray ionization mass spectrometry

    RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 4 2010
    Cheng Guo
    The fragmentation pathways of lithiated ,,, -unsaturated thioesters with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive ion mode. In mass spectrometry of the ,,, -unsaturated thioesters, Ar-CHCH-CO-S-Ph, loss of PhSLi and elimination of a thiophenol were the two major fragmentation reactions of the lithiated molecules. The elemental compositions of all the ions were confirmed by high-resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS). The thioesters studied here were para -monosubstituted on the phenyl ring of cinnamoyl and the electron-withdrawing groups favored loss of a thiophenol, whereas the electron-releasing groups strongly favored the competing reaction leading to the loss of PhSLi to form a cinnamoyl cation, Ar-CHCHCO+. The intensity ratios of the two competitive product ions were well correlated with the , substituent constants. The mechanisms of these two competing routes were further investigated by density functional theory (DFT) calculations. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Synthesis and Properties of para -Substituted NCN-Pincer Palladium and Platinum Complexes

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2004
    Martijn Q. Slagt Dr.
    Abstract A variety of para -substituted NCN-pincer palladium(II) and platinum(II) complexes [MX(NCN-Z)] (M=PdII, PtII; X=Cl, Br, I; NCN-Z=[2,6-(CH2NMe2)2C6H2 -4-Z],; Z=NO2, COOH, SO3H, PO(OEt)2, PO(OH)(OEt), PO(OH)2, CH2OH, SMe, NH2) were synthesised by routes involving substitution reactions, either prior to or, notably, after metalation of the ligand. The solubility of the pincer complexes is dominated by the nature of the para substituent Z, which renders several complexes water-soluble. The influence of the para substituent on the electronic properties of the metal centre was studied by 195Pt NMR spectroscopy and DFT calculations. Both the 195Pt chemical shift and the calculated natural population charge on platinum correlate linearly with the ,p Hammett substituent constants, and thus the electronic properties of predesigned pincer complexes can be predicted. The ,p value for the para -PtI group itself was determined to be ,1.18 in methanol and ,0.72 in water/methanol (1/1). Complexes substituted with protic functional groups (CH2OH, COOH) exist as dimers in the solid state due to intermolecular hydrogen-bonding interactions. Een verscheidenheid aan para-gesubstitueerde NCN-pincer-palladium(II) en -platina(II) complexen [MX(NCN-Z)] (M=PdII, PtII; X=Cl, Br, I; NCN-Z=[2,6-(CH2NMe2)C6H2 -4-Z],; Z=NO2, COOH, SO3H, PO(OEt)2, PO(OH)(OEt), PO(OH)2, CH2OH, SMe, NH2) is gesynthetiseerd via substitutiereacties zowel voor, en hoogst opmerkelijk, ook na de metallering van het ligand. De oplosbaarheid van de pincer-complexen wordt gedomineerd door de aard van de para -substituent Z, waardoor enkele van de complexen wateroplosbaar zijn. De invloed van de para -substituent op de elektronische eigenschappen van het metaalcentrum is bestudeerd met behulp van195Pt-NMR en DFT-berekeningen. Zowel de chemische verschuiving van de195Pt-kern, als de berekende ,natural population, lading op platina vertonen een lineaire correlatie met de ,pHammett-substituentconstante, hetgeen het voorspellen van de elektronische eigenschappen van nieuwe pincercomplexen mogelijk maakt. De ,p -waarde van de para-PtI eenheid blijkt respectievelijk ,1.18 in methanol en ,0.72 in waterige methanol (1/1, v/v) te zijn. Door de aanwezigheid van intermoleculaire waterstofbruggen komen de complexen met protische functionele groepen (CH2OH, COOH) in de vaste stof voor als dimeren. [source]