The kinetics of the chlorine isotopic exchange between chloride ion at O,O-diarylphosphorochloridates or O,O-diarylphosphorochloridothionates

The kinetics of the chlorine isotopic exchange reaction between tetraethylammonium chloride-³⁶Cl and O,O-diarylphosphorochloridates (p-RC₆H₄O)₂POCl or O,O-diarylphosphorochloridothionates (p-RC₆H₄O)₂PSCl has been studied in acetonitrile solution. Good Hammett's correlations of the rate constants with Taft's σ⁰ constants were obtained. The values of the reaction constants ρ were found identical for phosphoryl and thiophosphoryl compounds. In comparison with oxygen in the phosphoryl group, the sulfur atom exhibits an electron-donating effect (Δσ⁰ ～ 0.80). No correlation has been found for the enthalpy and entropy of activation. The effect of the substituents aryloxy groups, oxygen, or sulfur atoms in the phosphoryl group on the kinetics of the S_N2-P reaction is discussed. The reactivity of the investigated compounds is determined by the extent of the positive charge localized on the phosphorus atom. The positive charge is formed by the direct interactions of the substituents with the reaction center and the indirect–intramolecular interactions revealed in the structure of the compound.     

Novel Ortho effects detected in the fast atom bombardment mass spectra of substituted bisaryl phosphate antagonists of platelet-activating factor

A series of substituted bisaryl phosphate compounds, (R¹CH₂)⁺ ArOP = O(O^?)(OArR²R₃), was analyzed and characterized by fast atom bombardment mass spectrometry. Abundant fragment ions were observed and correlated with the proposed structures. From fragmentation pattersn, ‘ortho effect’ reactions were demonstrated to have occurred when the phosphoryl oxygen reacted with the (CH₂R¹)⁺ and C?O(OCH₃) substituents in the ortho position, relative to the phosphate group, and displaced the R¹ and OCH₃ groups, respectively, to produce phosphorus containing six-membered rings fused to the aryl moiety. When the (CH₂R¹)⁺ substituents were in the meta position relative to the phosphate group, the ‘ortho effect’ reactions were not observed. However, when the C?O(OCH₃) substituent was in the meta position relative to the phosphate group, an abundant fragment ion containing a five-membered phosphate ring fused to the aryl ring was detected with the original phosphoryl oxygen ortho to both the phosphate oxygen and a formyl group, formed from the original C?O(OCH₃) substituent. All other fragmentations not involving the ‘ortho effect’ reactions were nearly identical for the different structural isomers of the substituted bisaryl phosphate compounds.     

SYNTHESIS AND NMR SPECTROSCOPIC INVESTIGATION OF PHENYLPHOSPHORYL DERIVATIVES

Abstract

The syntheses of 16 phenyl- (1 and 3) and phenylthiophosphoryl (2) derivatives are described. The ¹³C and ¹⁷O NMR data sensitively reflect electron density changes in the phosphoryl substituents caused by p^π–d^π back-donation from X/Y to P. Taft constants σ₁ and σ_R ⁰ were derived for 16 phosphoryl substituents.     

Enolization of the phosphoryl group

Enolization of the phosphoryl group has been studied where Y = PPh₃, CN, Ts, COOEt, CONEt₂; R and R′ = Et, Bu, Ph, EtO, BuO, PhO; and X = Cl, Br, ClO₄, BF₄. It has been established that substances with are phosphaenols, but in substances with Y = CONEt₂ the phosphoryl group cannot be enolized under any conditions. Phosphaenolization is favored by a high acidifying ability of the Y group, the ability of the X anion to stabilize the phosphaenolic form due to formation of a hydrogen bond OH…X with the anion, and a low electronegativity of R and R′ groups. To evaluate the acidifying ability of Y, this article defines specific σ⁻ constants dependent on the number of substituents at the α-carbon atom: σ_CH3⁻, σ_CH2⁻ and σ_CH⁻. Their sums characterize the enolization ability of the phosphoryl group. The enolic structure in the solid state is possible if ∑_CHn⁻ > 2. If this sum lies in the range of 2 < ∑_CHn⁻ < 2.6 the phosphoryl–phosphaenol tautomerism can be expected in appropriate solutions. Acidic properties of the investigated compounds in MeNO₂ and EtOH (absolute) have been determined. Calculations of the acidity of the phosphoryl CH forms (A) and of the phosphaenol OH forms (B) have been carried out.     

Direct and indirect substituent effects on 1J(CH) in vinyl derivatives and related compounds

The variation in the one–bond couplings ¹J(CH) in vinyl derivatives with substituent has been examined. For the geminal proton ¹J correlates very badly with substituent electronegativity but extremely well with σ_I, if conjugating substituents are excluded. In the case of halogen substituents the marked stereospecificity of ¹J(CH) for the cis and trans protons can be rationalised in terms of an intrinsic dependence of π_CH on the dihedral angle between the coupling atoms and the perturbing substituent, with an additional positive increment to the cis coupling due to direct interaction of the substituent non-bonding electrons or to orbital circulation of the substituent electrons. The intrinsic specificity of β-substituent effects on ¹J(CH) is also found in analogous compounds containing C?N and C?O bonds.     

1,3-Dioxolanylium- und 1,3-Dioxanylium-Derivate via Protonenkatalysierte SNi-Reaktionen in der Gasphase

By means of chemical ionization 1,3-dioxolanylium as well as 1,3-dioxanylium ions are formed in proton catalysed S_Ni assisted heterolysis in the gas phase. The effects of both constitution and configuration are discussed and compared with the results of analogous reactions in the condensed phase. It is shown that the unimolecular decompositions of [MH]⁺ ions containing two vicinal substituents, e.g. Br or OAc, are not governed by the proton affinity of the departing neutrals HBr or HOAc, respectively. The findings partially contradict the results on HX loss (X: substituent) from protonated monosubstituted compounds.     

Specific Interaction Between Negative Atmospheric Ions and Organic Compounds in Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry

The interaction between negative atmospheric ions and various types of organic compounds were investigated using atmospheric pressure corona discharge ionization (APCDI) mass spectrometry. Atmospheric negative ions such as O₂^–, HCO₃^–, COO^–(COOH), NO₂^–, NO₃^–, and NO₃^–(HNO₃) having different proton affinities served as the reactant ions for analyte ionization in APCDI in negative-ion mode. The individual atmospheric ions specifically ionized aliphatic and aromatic compounds with various functional groups as atmospheric ion adducts and deprotonated analytes. The formation of the atmospheric ion adducts under certain discharge conditions is most likely attributable to the affinity between the analyte and atmospheric ion and the concentration of the atmospheric ion produced under these conditions. The deprotonated analytes, in contrast, were generated from the adducts of the atmospheric ions with higher proton affinity attributable to efficient proton abstraction from the analyte by the atmospheric ion.     

Studies on organophosphorus compounds 52.Structure-reactivity studies of organophosphorus compounds by MNDO calculations

MNDO and MM2(85)methods were used to study the conformation and the structure-reactivity relationship of neutral and acidic phosphorus esters.The calculation results indicate thatfor the most stable conformation,the charge density of phosphoryl oxygen(q_O)is determined notonly by the electronegativity of the substituents,but also by the conformation of the alkoxyl groupson the phosphorus atom.Meanwhile,the conformation of the alkoxyl group provides,as a rule,more important influence on the charge density of the phosphoryl oxygen.However,the energy ofthe highest occupied molecular orbital(EHOMO)is basically dependent on the eletronegativity of thesubstituents,while the donating ability or the withdrawing ability of the neutral phosphorus com-pounds is mainly governed by the EHOMO but not the q_O.This is also true for other kinds of theneutral oxygen-containing compounds.     

Adducts of niobium(V) and tantalum(V) halides. XIV. Structure and relative stability of the adducts with some phosphoryl compounds

The adducts of niobium(V) and tantalum(V) halides with some phosphoryl compounds have been studied in chloroform solution by ¹H- and ¹⁹F-FT-NMR. spectroscopy. These octahedral adducts of general formula MX₅ · L (M = Nb, Ta; X = F, Cl, Br; L = phosphoryl ligand) are monomeric and neutral. Their relative stability constants have been determined at ?60°. The stabilities are controlled by electronic effects of substituents on the phosphoryl group.     

Effect of the substituents on the conformational behavior of five-membered rings: Application to the cis- and trans-2,5-dimethoxytetrahydrofuran

A model is proposed which assumes that the pseudorotational potential in five-membered rings is given by the combination of contributions from the unsubstituted ring, from the individual substituents and from interactions between pairs of substituents. The application of this model to the potentials calculated by the MM2 force field for the cis and trans-2,5-dimethoxytetrahydrofuran shows that the contributions from the individual substituents explain the main features of the potentials of these disubstituted rings. The pseudorotational analysis from vicinal proton spin-spin coupling constants ³J_HH confirms the realibility of the MM2 potentials.     

Density functional theory investigation of the binding interactions between phosphoryl,carbonyl, imino,and thiocarbonyl ligands and the pentaaqua nickel(II) complex: Coordination affinity and associated parameters

Density Functional Theory (UB3LYP/6‐311++G(d,p)) calculations of the affinity of the pentaaqua nickel(II) complex for a set of phosphoryl [O?P(H)(CH₃)(PhR)], imino [HN?C(CH₃)(PhR)], thiocarbonyl [S?C(CH₃)(PhR)] and carbonyl [O?C(CH₃)(PhR)] ligands were performed, where R?NH₂, OCH₃, OH, CH₃, H, Cl, CN, and NO₂ is a substituent at the para‐position of a phenyl ring.The affinity of the pentaaqua nickel(II) complex for these ligands was analized and quantified in terms of interaction enthalpy (ΔH), Gibbs free energy (ΔG²⁹⁸), geometric and electronic parameters of the resultant octahedral complexes. The ΔH and ΔG²⁹⁸ results show that the ligand coordination strength increases in the following order: carbonyl < thiocarbonyl < imino < phosphoryl. This coordination strength order is also observed in the analysis of the metal‐ligand distances and charges on the ligand atom that interacts with the Ni(II) cation. The electronic character of the substituent R is the main parameter that affects the strength of the metal‐ligand coordination. Ligands containing electron‐donating groups (NH₂, OCH₃, OH) have more exothermic ΔH and ΔG²⁹⁸ than ligands with electron‐withdrawing groups (Cl, CN, NO₂). The metal‐ligand interaction decomposed by means of the energy decomposition analysis (EDA) method shows that the electronic character of the ligand modulates all the components of the metal‐ligand interaction. The absolute softness of the free ligands is correlated with the covalent contribution to the instantaneous interaction energy calculated using the EDA method. © 2013 Wiley Periodicals, Inc.     

Theoretical study of substituent effects on the acidity of the methyl group: Structure of anions CH2X−

Geometries have been optimized using molecular-orbital calculations (a) with a 4-31G Gaussian basis set for carbanions CH₂X^? where X = H, CH₃, NH₂, OH, F, C?CH, CH?CH₂, CHO, COCH₃, CN, and NO₂; and (b) with an STO -3G basis set for methyl acetate and acetyl deprotonated methyl acetate. All the carbanions containing unsaturated substituents are planar, with a considerable shortening of the C? X bond. Carbanions containing saturated substituents are pyramidal with the out-of-plane angle α increasing with the electronegativity of the substituent. Double-zeta basis set calculations give proton affinities over the range 449 (for CH₃CH₂^?) to 355 kcal/mol (for CH₂NO₂^?), with all unsaturated anions having smaller affinities than saturated anions. The correlation of proton affinities with 1s binding energies, and with charges on both the carbon of the anion and on the acidic proton of the neutral molecule are examined.     

The proton affinity of thioformaldehyde. Implications for the heat of formation of thioformaldehyde and thiolmethyl carbonium ion from ion cyclotron resonance investigations of the proton transfer reactions of [CH2SH]+

Ions at m/z 47 have been generated from a variety of organosulfur compounds both at 70 eV and near threshold. From observations of the energetics of proton transfer from m/z 47 to reference bases of known proton affinity, the species obtained in all cases has been shown to be [CH₂SH]⁺ rather than [CH₃S]⁺. This result is shown to be consistent with recent ab initio calculations on these two isomers and collisional activation experiments.     

Magnetic non-equivalence in carbinols of the general formula R1R2C(OH)CH2OR (1H and 13C NMR)

Several compounds of the general formula R¹R²C(OH)CH₂OR containing different geminal group systems have been investigated in proton and carbon magnetic resonances at variable temperatures. The role of steric factors, viz. of the size of substituents and the distances between different parts of the molecules, have been discussed.     

The relationship between proton–proton NMR coupling constants and substituent electronegativities. II—conformational analysis of the sugar ring in nucleosides and nucleotides in solution using a generalized Karplus equation

The relationship between vicinal NMR proton–proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on ³J(HH); second, empirical correlations between the parameters governing the conformation of β-D -furanosides (taken from an analysis of 178 crystal structures) were used to define proton–proton torsion angles as a function of the pseudorotation parameters P and Φ_m; and, third an iterative least-squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′-cyclic nucleotides, a base-stacked ribonucleotide, 2′-anhydroarabinonucleosides, α-D -2′,2-O-cyclouridine, 2′- and 3′-aminosubstituted ribonucleosides, 2′- and 3′-deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.     

Reactivity of a N-Coordinated Germylene-Borane Complex: From Ge→B to Ge→Ga Coordination

Reactivity studies of the Ge^II→B complex L(Cl)Ge⋅BH₃ ( 1 ; L=2-Et₂NCH₂-4,6-tBu₂-C₆H₂) were performed to determine the effect on the Ge^II→B donation. N-coordinated compounds L(OtBu)Ge⋅BH₃ ( 2 ) and [LGe⋅BH₃]₂ ( 3 ) were prepared. The possible tuning of the Ge^II→B interaction was proved experimentally, yielding compounds 1-PPh₂-8-(LGe)-C₁₀H₆ ( 4 ) and L(Cl)Ge⋅GaCl₃ ( 5 ) without a Ge^II→B interaction. In 5 , an unprecedented Ge^II→Ga coordination was revealed. The experimental results were complemented by a theoretical study focusing on the bonding in 1 − 5 . The different strength of the Ge^II→E (E=B, Ga) donation was evaluated by using energy decomposition analysis. The basicity of different L(X)Ge groups through proton affinity is also assessed.     

How Does the Fluorination of the Linker Affect the Structural Chemistry of Trimesate-Based Metal-Organic Frameworks (MOFs)?

FMOFs, i.e. metal-organic frameworks with linkers with fluoro substituents, were supposed to show enhanced thermal and chemical stability as well as high gas affinity and hydrophobicity. However, at least for aromatic carboxylate ligands it was shown in a subsequent work that fluoro substituents weaken the C(phenyl)-COO^– bond and thus facilitate decarboxylation leading to a decreased chemical and thermal stability. Nonetheless, it was concluded that linker fluorination leads to a rich structural chemistry, as the torsion angle between the phenyl ring and the carboxylate group is significantly increased in these compounds. Here, we present the very first examples of four MOFs all based on Sr²⁺ cations and trimesate-based linkers with three different degrees of fluorination as well as the known non-fluorinated counterpart: [Sr(HL)(H₂O)] · n H₂O [ 1 : L = mF-BTC^3–, n = 0.5, P1 , Z = 2; 2 : L = dF-BTC^3–, n = 0.5, C2/c, Z = 8; 3 : L = pF-BTC^3–, n = 1.5, C2/c, Z = 8; 4 : L = BTC^3–, n = 0.5, P1 , Z = 2; BTC^3– ≡ 1,3,5-benzenetricarboxylate (trimesate); mF-BTC^3– ≡ monofluorinated trimesate, dF-BTC^3– ≡ difluorinated trimesate, pF-BTC^3– ≡ per-(tri-)fluorinated trimesate]. Whereas 1 and known 4 are found to crystallize in isotypic structures and 2 in a very similar structural arrangement [all CN(Sr²⁺) = 9], 3 with the highest degree of fluorination exhibits a completely different crystal structure [CN(Sr²⁺) = 8], which is already obvious from the different composition. It is shown that the torsion angles between the phenyl ring and the carboxylate groups play an important structure-directing role. DSC/TGA investigations confirm that with increasing fluorination the thermal stability is decreased. However, the release temperature of water, i.e. the affinity to water, increases with the number of fluoro substituents.     

Mono-Phosphazenyl Phosphines (R2N)3P=N–P(NR2)2 – Strong P-Bases,P-Donors,and P-Nucleophiles for the Construction of Chelates

We present a convenient three-step synthesis of amino substituted phosphazenyl phosphines of the general formula (R₂N)₃P=N–P(NR₂)₂ [NR₂ = N(CH₂)₄, N(CH₂)₅, N(CH₂)₆]. These easily accessible mixed valent compounds display a surprisingly high proton affinity and basicity in the same range as the corresponding Schwesinger diphosphazene (Me₂N)₃P=N–P=NEt(NMe₂)₂ (Et-P₂) and Verkade's proazaphosphatrane superbases. Within the central [P^III–N=P^V] scaffold, the phosphine P^III and not the phosphazene N^III atom is the center of highest proton affinity, basicity and donor strength. As P-bases, the title compounds display calculated proton affinities between 265.8 (NR₂ = NMe₂) and 274.7 kcal · mol^–1 [NR₂ = N(CH₂)₄] and pK_BH⁺ values between 26.4 (NR₂ = NMe₂) and 31.5 [NR₂ = N(CH₂)₄] on the acetonitrile scale. As P-nucleophiles, they are key intermediates in the synthesis of hyperbasic bis(diphosphazene) proton sponges, chiral bis(diphosphazene) proton pincers, bisphosphazides, and superbasic P₂-bisylides. Their Staudinger reactions as nucleophile towards 1,8-diazidonaphthalene leading to 1,8-naphthalene-bisphosphazides is described in detail. The donor strength of the title compounds towards fragments [Se] and [Ni(CO)₃] is in the same range as that of N-heterocyclic carbenes.     

Substituent effects on the gas‐phase fragmentation reactions of protonated peptides containing benzylamine‐derivatized lysyl residues

Motivated by the need for chemical strategies designed to tune peptide fragmentation to selective cleavage reactions, benzyl ring substituent influence on the relative formation of carbocation elimination (CCE) products from peptides with benzylamine‐derivatized lysyl residues has been examined using collision‐induced dissociation (CID) tandem mass spectrometry. Unsubstituted benzylamine‐derivatized peptides yield a mixture of products derived from amide backbone cleavage and CCE. The latter involves side‐chain cleavage of the derivatized lysyl residue to form a benzylic carbocation [C₇H₇]⁺ and an intact peptide product ion [(MH_n)ⁿ⁺ – (C₇H₇)⁺]^(n‐1)+. The CCE pathway is contingent upon protonation of the secondary ε‐amino group (N_ε) of the derivatized lysyl residue. Using the Hammett methodology to evaluate the electronic contributions of benzyl ring substituents on chemical reactivity, a direct correlation was observed between changes in the CCE product ion intensity ratios (relative to backbone fragmentation) and the Hammett substituent constants, σ, of the corresponding substituents. There was no correlation between the substituent‐influenced gas‐phase proton affinity of N_ε and the relative ratios of CCE product ions. However, a strong correlation was observed between the π orbital interaction energies (ΔE_int) of the eliminated benzylic carbocation and the logarithm of the relative ratios, indicating the predominant factor in the CCE pathway is the substituent effect on the level of hyperconjugation and resonance stability of the eliminated benzylic carbocation. This work effectively demonstrates the applicability of σ (and ΔE_int) as substituent selection parameters for the design of benzyl‐based peptide‐reactive reagents which tune CCE product formation as desired for specific applications. Copyright © 2012 John Wiley & Sons, Ltd.     

Correlation of 2-, 3-, 4- and disubstituted pyridine gas-phase proton affinities with ab initio calculated energies at the sto-3g basis set level

Total energies of 2-, 3-, 4- and disubstituted pyridines were calculated for the salt and the free base using ab initio molecular orbital calculations at the STO-3G basis set level [2]. In each set, the difference in energy, ΔE_H, between the salt and the free base was calculated and plotted against experimentally derived gas-phase proton affinities. The correlation was very good for each of the substituent categories listed. All of the energies and proton affinities were then plotted together on the same graph. The result was an excellent correlation with r = 0.97. The linear equation for gas phase proton affinity, PA_B = 28.51 + 435.45ΔE_H kcal/mole, was derived from this plot and was used to calculate proton affinities for all of the thirty-one compounds used in this study as well as for a series of dicyanopyridines for which values of proton affinity are not available at this time.