13C?13C spin coupling constants in tetrahydronaphthylene,hexahydrobenzanthracene and benzo[a]pyrene derivatives

The ¹³C? ¹³C spin coupling constants have been determined in substituted [1-¹³C]tetrahydronaphthylenes, [5-¹³C]hexahydrobenzanthracenes and [5-¹³C]benzanthracene. In addition, the ¹³C? ¹³C spin coupling constants for 7-hydroxy[7-¹³C]benzopyrene, trans-7,8-dihydro[7-¹³C]benzopyrene-7,8-diol and trans-7,8-dihydro[10-¹³C]benzopyrene-7,8-diol are reported, together with the one-bond carbon-carbon coupling constants between C-4 and C-5 in selected 4,5-disubstituted benzopyrenes. Values for the directly bonded coupling constants and long-range coupling constants are similar to those reported previously for other aromatic and aliphatic systems. Substituent effects on carbon-carbon coupling are compared for similarly substituted cyclic and acyclic systems.     

Precise values of the 13C component vicinal coupling constants for calculating side-chain conformations in amino acids

From consideration of ¹H–¹H vicinal coupling constants and ¹³C? ¹H long-range coupling constants in a series of amino acid derivatives, the precise values of ¹³C component vicinal coupling constants have been calculated for the three minimum energy staggered rotamers for the C(α)H? C(β)H₂ side-chains of amino acids.     

Ab initio Study of Anharmonic Force Field and Spectroscopic Constants for Germanium Dichloride

Ab initio study of the equilibrium structure, spectroscopy constants, and anharmonic force field for several isotopomers of germanium dichloride (⁷⁰GeCl₂, ⁷²GeCl₂, and ⁷⁶GeCl₂) have been carried out at the MP2 and CCSD(T) levels of theory using cc-pVTZ basis set. The calculated geometries, rotational constants, vibration-rotation interaction constants, harmonic frequencies, anharmonic constants, quartic and sextic centrifugal distortion constants, cubic and quartic force constants are compared with experimental data. For small mass differences of the Ge isotopes, the isotopic effects for germanium dichloride are much weaker. The agreements are satisfactory for these two methods, but the deviations of CCSD(T) results are slightly larger than that of MP2, because of CCSD(T)'s inadequate treatment of electron correlation in hypervalent Cl atom.     

Rate constants for the reactions of the OH radical with the propyl and butyl nitrates and 1-nitrobutane at 298 ± 2 k

Using a relative rate method, rate constants for the gas-phase reactions of the OH radical with 1- and 2-propyl nitrate, 1- and 2-butyl nitrate and 1-nitrobutane have been determined in the presence of one atmosphere of air at 298 ± 2 K. Using rate constants for the reactions of the OH radical with propane and cyclohexane of 1.15 × 10^?12 and 7.49 × 10^?12 cm³ molecule^?1 s^?1, respectively, following rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) were obtained: 1-propyl nitrate, 0.62; 2-propyl nitrate, 0.41; 1-butyl nitrate, 1.78; 2-butyl nitrate, 0.93; and 1-nitrobutane, 1.35. These rate constants are compared and discussed with the literature data.     

Thermodynamic studies of alkaline-earth-metal cation complexation by lipophilic dioxa,trioxa, and dithia dicarboxylic acids

Five new lipophilic dicarboxylic acids with systematic structural variation in the bridge which joins the two lipophilic carboxylic acid units have been synthesized. Potentiometric equilibrium measurements of hydrogen ion concentrations have been employed to determine the protonation constants for these lipophilic di-ionizable acyclic ligands in 90% methanol-10% water (v/v) at 25.0 °C and an ionic strength of 0.10 M and the stability constants for their complexes with Mg²⁺, Ca²⁺, and Sr²⁺. Although all five ligands exhibit the highest stability constants for Ca²⁺, the magnitude of the differences between the stability constants for complexation of Ca²⁺ versus Mg²⁺ or Sr²⁺ is found to vary widely depending upon the identity of the bridging unit which joins the two carboxylic acid end groups.     

13C?19F spin–spin coupling in some monofluoro-substituted polycyclic aromatic hydrocarbons

The determination and complete assignment of the ¹³C? ¹⁹F coupling constants and ¹³C chemical shifts for 15 monofluoro derivatives of nine polycyclic aromatic hydrocarbons are reported. Fluorine substitutent effects on the ¹³C chemical shifts are given and their regular behaviour, making comparisons between different compounds possible, is discussed. The numerical values of the ¹³C? ¹⁹F long range coupling constants are found, with a few exceptions, to decrease in an alternating manner along the periphery of the molecules. In several cases the signs of the coupling constants have been determined. It appears that the signs alternate, but additional evidence is required. The magnitudes of different types of coupling constants are discussed in terms of steric and electronic effects. CNDO/2 and INDO calculations of the ¹³C? ¹⁹F coupling constants in the fluoronaphthalenes have been performed using the ‘sum-over-states’ method with the aim of examining the orbital and spin–dipole contributions to the various couplings.     

Non-empirical calculations of the nuclear magnetic resonance spectra of imidazole and hydrated imidazole

The magnetic shielding constants of the ¹H, ¹³C and ¹⁵N nuclei of imidazole are calculated for the isolated and hydrated molecules. The results show that the hydrogen bonds produce not only large variations of the chemical shifts for the nitrogen nuclei and the NH proton which are directly involved in the intermolecular bonding, but also measurable shifts for the carbon nuclei. The calculated shielding constants and their variation with hydration are discussed in relation to experimental results concerning imidazole, the 5-membered ring of the purine bases and the imidazole ring of histidine. The calculated values of the spin-spin coupling constants confirm that it is possible to study the tautomeric equilibrium of the imidazole ring from the measurement of these coupling constants and that spin-spin coupling constants are not very sensitive to solvent effects.     

Structural effects on the rates of the ion molecule reactions of organic heterocycles

Rate constants for proton transfer reactions of seven heterocyclic amines, eight heterocyclic ethers and propylene sulfide have been measured by photoionization mass specrometry. Rate constants for dimerization of four sulfides have also been measured. The measured rate constants have also been compared to the theoretical (ADO) rate constants. In all cases the ADO rate constants show only small variations with structure. In fact for the mono-heterocycles all but one of the ADO rate constants are between 2.0 and 1.5 × 10^?9 cc molec^?1 sec^?1. The observed rate constants show considerable dependence on chemical structure. The amines react faster than the oxides which in turn react faster than the sulfides. N-Methyl substitution on pyrrolidine and piperidine lowers their rate constants by about a factor of two while, propylene oxide reacts eighteen percent faster than ethylene oxide. Examination of the variation in the observed rate constants as a function of ring size for each group of heterocycles indicates a distinct structure-reactivity correlation although we have not attempted to rationalize this correlation. There is also a structure-reactivity dependence observed in the six-membered oxygen heterocycles having a second heteroatom O, NH, or S in the 4-position. The rate constants increase with the electronegativity of the second heteroatom.     

NMR spectral studies of quinoline derivatives. Long range 13C?1H coupling constants in methylquinoline derivatives

Long range ¹³C? ¹H coupling constants are reported for a number of methylquinoline derivatives. The results have been compared with those observed in the pyridine series and correlated with ¹H? ¹H coupling constants.     

CHCl3电子吸附速率常数的离子迁移谱

The dissociative electron attachment process for CHCl₃ at different electric field have been studied with nitrogen as drift and carrier gas using corona discharge ionization source ion mobility spectrometry (CD-IMS). The corresponding electron attachment rate constants varied from 1.26×10^-8 cm³/(molecules s) to 8.24×10^-9 cm³/(molecules s) as the electric field changed from 200 V/cm to 500 V/cm. At a fixed electric field in the drift region,the attachment rate constants are also detected at different sample concentration. The ion-molecule reaction rate constants for the further reaction between Cl^- and CHCl₃ are also detected, which indicates that the technique maybe becomes a new method to research the rate constants between ions and neural molecules. And the reaction rate constants between Cl^- and CHCl₃ are the first time detected using CD-IMS.     

Investigation of two‐ and three‐bond carbon–hydrogen coupling constants in cinnamic acid based compounds

Two‐ and three‐bond coupling constants (²J_HC and ³J_HC) were determined for a series of 12 substituted cinnamic acids using a selective 2D inphase/antiphase (IPAP)‐single quantum multiple bond correlation (HSQMBC) and 1D proton coupled ¹³C NMR experiments. The coupling constants from two methods were compared and found to give very similar values. The results showed coupling constant values ranging from 1.7 to 9.7 Hz and 1.0 to 9.6 Hz for the IPAP‐HSQMBC and the direct ¹³C NMR experiments, respectively. The experimental values of the coupling constants were compared with discrete density functional theory (DFT) calculated values and were found to be in good agreement for the ³J_HC. However, the DFT method under estimated the ²J_HC coupling constants. Knowing the limitations of the measurement and calculation of these multibond coupling constants will add confidence to the assignment of conformation or stereochemical aspects of complex molecules like natural products. Copyright © 2016 John Wiley & Sons, Ltd.     

Rate constants for Hydrogen abstraction reactions of NO3 in aqueous solution

Rate constants have been measured by pulse radiolysis for the reactions of the NO₃ radical with five cyclic ethers and a series of alcohols. Rate constants ranged from 3.5 × 10⁴ M^×1 s^×1 for deuterated methanol to 1.1 × 10⁷ M^?1 s^?1 for tetrahydrofuran. The rate constants for the reactions of NO₃ with the alcohols 1-propanol to 1-heptanol were found to be linearly dependent on the number of CH₃ groups with a group reactivity of 6.4 × 10⁵ M^?1 s^?1.     

Natural abundance 13C13C coupling constants observed via double quantum coherence. The two-dimensional ‘inadequate’ experiment for 13C NMR spectral analysis of erythronolide - B

A one- and a two-dimensional INADEQUATE NMR experiment afforded one-bond ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1). ¹³C¹³C coupling constants at natural abundance and total unambiguous signal assignment for erythronolide-B (1).     

The determination of a π-sigma constant for substituents attached to silicon

The proton, ¹³C, and ²⁹Si chemical shifts and the ¹³C¹H coupling constants of a series of compounds of the type (CH₃)₃SiX were measured and correlated with inductive and resonance σ constants. In order to provide a comparison with a homologous series in which π-bonding is absent, shifts and coupling constants were obtained for the t-butyl series, (CH₃)₃CX. Only the coupling constants gave significant correlations with σ_I. A series of σ constants, presumably reflective of the amount of π-bonding, were obtained from the deviations from the J vs. σ_I plot. The magnitudes of these values indicate that oxygen is a better π-donor than nitrogen and chlorine.     

Force constants in molecular crystals of methyl-and perdeuteriomethylmercury(II) halides

Force constants for the internal vibrations involving the metal and for the lattice vibrations of Hg(CH₃)X and Hg(CD₃)X (X = Cl, Br or I) are calculated on the basis of a D_4h⁷ layer structure. The internal HgX stretching force constants are much lower than for these molecules in solution, but HgC stretching force constants are slightly higher. The HgX and longitudinal translatory force constants within the lattice layer are close in value to the strong and weak HgX bond stretching force constants respectively in the unsymmetrical [Hg(CH₃)X₂]^? complex ions.     

Rate constants for the gas-phase reactions of O3 with a series of carbonyls at 296 K

Rate constants for the gas-phase reactions of O₃ with the carbonyls acrolein, crotonaldehyde, methacrolein, methylvinylketone, 3-penten-2-one, 2-cyclohexen-1-one, acetaldehyde, and methylglyoxal have been determined at 296 ± 2 K. The rate constants ranged from <6 × 10^?21 cm³ molecule^?1 s^?1 for acetaldehyde to 2.13 × 10^?17 cm³ molecule^?1 s^?1 for 3-penten-2-one. The substituent effects of ? CHO and CH₃CO? groups on the rate constants are assessed and discussed, as are implications for the atmospheric chemistry of the natural hydrocarbon isoprene.     

Carbon-13 NMR studies of monohydroxylated and monochlorinated derivatives of Z- and E-p-menthanes

J(¹³C¹H) coupling constants for some methyl- and aminopyrimidines have been determined by ¹³C NMR. Both the one-bond and long-bond and long-range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the ³J(C-i,H) coupling constants between a ring carbon C-i and the ring protons are larger than the ²J(C-i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: ³J(C,Me). These general rules are very useful for the assignment of resonances in complex ¹³C spectra of pyrimidines and seem to be valid for other 6-membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on ¹J (CH) for monosubstituted pyrimidines allows the estimation of ¹J (CH) for polysubstituted pyrimidines with a very good accuracy.     

Effects of ring strain on gas-phase rate constants. 2. OH radical reactions with cycloalkenes

Relative rate constants for the gas-phase reactions of OH radicals with a series of cycloalkenes have been determined at 298 ± 2 K using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with isoprene of 9.60 × 10^?11 cm³ molecule^?1 s^?1, the rate constants obtained were (X 10¹¹ cm³ molecule^?1 s^?1): cyclopentene 6.39 ± 0.23, cyclohexene 6.43 ± 0.17, cycloheptene 7.08 ± 0.22, 1,3-cyclohexadiene 15.6 ± 0.5, 1,4 cyclohexadiene 9.48 ± 0.39, bicyclo[2.2.1]-2-heptene 4.68 ± 0.39, bicyclo[2.2.1] 2,5 heptadiene 11.4 ± 1.0, and bicyclo[2.2.2] 2 octene 3.88 ± 0.19. These data show that the rate constants for the nonconjugated cycloalkenes studied depend on the number of double bonds and the degree of substitution per double bond, and indicate that there are no obvious effects of ring strain energy on these OH radical addition rate constants. A predictive technique for the estimation of OH radical rate constants for alkenes and cycloalkenes is presented and discussed.     

Potentiometric Study of the Chelates of Al(III), Ce(IV) and Th(IV) with Alizarin Red S

The stepwise metal-ligand stability constants of ARS chelates with Al³⁺, Ce¹⁺ and Th⁴⁺ have been determined by using Bjerrum-Calvin technique. Various computational methods were used to determine the stability constants. The thermodynamic stability constants were also calculated by determining the stepwise stability constants at various ionic strengths and then by extrapolating to zero ionic strength. The order of stability constants was found to be: Th>Al>Ce.     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.