摘要:

The dynamics and conformation ofN,N-dimethyl-N-|3-(benzoyl-4-phenoxy)|-N-n-dodecylammonium bromide,1, have been established in two solvents (CDCl3and DMSO-d6) by the use of13C spin-lattice relaxation rates, non-selective and selective proton spin-lattice relaxation rates, and1H–{1H} nuclear Overhauser enhancement (nOe) experiments. The data obtained are consistent with two main mean conformations for compound1: a "linear" conformation in CDCl3and a folded conformation in DMSO-d6where the alkyl chain forms a loop toward the aromatic moiety.Keywords: UV filter, carbon and proton relaxation rates, nuclear Overhauser enhancement experiments, solvent dependent conformations.

ISSN:0008-4042    

DOI:10.1139/v91-135

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The1H nuclear magnetic resonance spectra of 2-isopropylbenzaldehyde in CS2/C6D12and acetone-d6solutions provide the chemical shifts and coupling constants of all the protons. The long-range coupling constants involving the side-chain protons yield certain sums of the populations of the four putatively planar conformations. Theo-anticonformers have a fractional population of 0.55(3) in the polar and of 0.49(3) in the nonpolar solvent. The conformers in which the methine C—H bond liescisto the aldehyde group have a fractional population of 0.83(3) in both solutions. The close approach of the methine and aldehydic hydrogen atoms in one conformer is indicated by a negative proximate coupling constant between their protons of –0.39(1) Hz. The chemical shifts of the ring and of the side-chain protons are consistent with the conformer populations deduced from the long-range coupling constants and also with the indications that the side chains do not, on average, deviate from "coplanarity" with the ring by much more or less than in the parent compounds. The C—H … H—C and C—H … O=C interactions in theo-synando-anticonformers are most likely repulsive and of very similar magnitude and lead to a significant deshielding of the protons in these moieties. Molecular orbital computations are also reported and are an aid in estimating the populations of the individual conformers. The STO-3G MO structures have H … H and H … O distances well below the sums of the van der Waals radii of hydrogen and oxygen atoms in the conformers with the methine C—H bond placedcisto the aldehyde group, yet these are computed to be by far the most abundant by the STO-3G as well as by AM1 algorithms.Keywords: 2-isopropylbenzaldehyde, conformations of; 2-isopropylbenzaldehyde, proximate spin–spin coupling constants in; MO calculations, STO-3G, and AM1 on 2-isopropylbenzaldehyde,1H NMR and long-range spin–spin coupling constants in 2-isopropylbenzaldehyde.

ISSN:0008-4042    

DOI:10.1139/v91-136

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The inversion potentials, obtained from STO-3G, STO-3G(*), 3-21G, 3-21G(*), and 4-31G basis sets, are reported for thianthrene and thioxanthene, molecules in which both or only one of the methylene groups have been replaced by sulfur in 9,10-dihydroanthracene. Comparison with the available experimental data suggests that the split-valence bases lead to an overestimate, possibly by about 10 kJ/mol, of the inversion barrier in the crystal, whereas the STO-3G and STO-3G* basis sets underestimate this barrier. It appears that the inversion barrier for thianthrene is much lower in solution than in the crystal. The long-range coupling constants between the methylene and ring protons for thioxanthene in solution are consistent with an inversion barrier somewhat smaller than those obtained with the split-valence bases but rather larger than those predicted with the STO-3G basis set. The bond lengths and angles in the equilibrium structures of the two molecules, as computed with the 3-21G(*) basis, agree reasonably well with those in their crystals, except that the theoretical folding angles are smaller than measured. These discrepancies become less marked when expectation values are calculated from the theoretical inversion potentials at finite temperatures.Keywords: MO calculations, inversion potentials of thianthrene and thioxanthene;1H NMR, thioxanthene; spin–spin coupling constants, long range, in thioxanthene.

ISSN:0008-4042    

DOI:10.1139/v91-137

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

α,β-Unsaturated thiol esters could be readily prepared via a Wadsworth–Emmons reaction using diethyl alkylthiocarbonylmethylphosphonate, which proved to be superior in reactivity to the corresponding Wittig reagent.Keywords: α,β-unsaturated thiol esters, Wadsworth–Emmons reaction.

ISSN:0008-4042    

DOI:10.1139/v91-138

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An excess concentration of base quinine (Q) reacts with a sulphonphthalein diacidic dye XH2, (bromocresol green, BCGH2, or bromophenol blue, BPBH2) in dichloromethane solution to form an ion associate (X2−(QH+)2) of stoichiometry 1:2 (dye:amine). Benzethonium chloride (ClB) reacts with the 1:2 ion associate to form an ion associate (QH+,X2−,B+) and quinine hydrochloride ClQH+. This substitution reaction is a chemical equilibrium with formation constants of 1.50 ± 0.67, 1.61 ± 0.54, 1.07 ± 0.29, 1.04 ± 0.20, and 0.84 ± 0.26 for BCG and 1.86 ± 0.59, 1.47 ± 0.23, 1.40 ± 0.65, 1.13 ± 0.37, and 1.11 ± 0.27 for BPB at 283.16, 288.16, 293.16, 298.16, and 303.16 K respectively. The thermodynamic parameters determined by van't Hoff's equation are ΔH0 = −21.766 ± 7.482 kJ mol−1, ΔS0 = −73 ± 51 J mol−1K−1, and ΔG0 = −1.134 ± 0.972 kJ mol−1for BCG and ΔH0 = −18.678 ± 7.482 kJ mol−1, ΔS0 = −61 ± 26 J mol−1K−1, ΔG0 = −0.916 ± 0.401 kJ mol−1for BPB (ΔG0at 293.16 K; and ΔH0and ΔS0determined in the range 283–303 K).Keywords: bromocresol green – quinine–benzethonium, ion associate mixture, bromophenol blue – quinine–benzethonium, equilibrium constants, thermodynamic parameters.

ISSN:0008-4042    

DOI:10.1139/v91-139

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The pKavalues for the deprotonation of a series of eight 1-(X-benzyl)-4-phenylacetylpyridinium cations (6) have been measured in aqueous solutions of ionic strength 0.1 at 25 °C: pKa = −0.18σ + 8.91. The pseudo-first-order rate constants for deprotonation of these carbon acids have been measured over the range pH = 11–13, and have been found to display kinetic saturation effects that are consistent with the addition of hydroxide ion to the carbonyl group (pKz) as the product of kinetic control upon basification of neutral aqueous solutions of these pyridinium cations, with the subsequent transformation of this anionic hydrate to the thermodynamically more stable enolate conjugate base. Analysis of the pH–rate profiles gives substituent effects upon pKz(ρ = −0.19) and upon the second-order rate constant (kOH(ρ = 0.09)) for deprotonation of6by hydroxide ion.Keywords: carbon acids, deprotonation, pKa, kinetics, substituent effects.

ISSN:0008-4042    

DOI:10.1139/v91-140

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A detailed study directed toward the development of a versatile synthetic route to the interesting dimeric natural product yuehchukene (1) and its epimer, 6a-epi-yuehchukene (2), has been completed. Due to the anti-implantation activity associated with1, it was important to provide a synthetic strategy not only to1, but to a family of yuehchukene analogues that, hopefully, would reveal superior chemical stability and (or) elevated biological activity. The experiments described herein and which utilize the readily available and inexpensive isophorone (6) satisfy these requirements.Keywords: yuehchukene synthesis, yuehchukene analogues, anti-implantation activity.

ISSN:0008-4042    

DOI:10.1139/v91-141

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The13C nuclear magnetic resonance spectra of 17 3,6-disubstituted pyridazine derivatives have been systematically analyzed. Chemical shifts and various13C,1H coupling constants are reported. Attempts were made to correlate these data with results obtained from semiempirical molecular orbital calculations as well as with substituent electronegativities and Taft's substituent constants σIand σR0.Keywords: 3,6-disubstituted pyridazines,13C NMR spectroscopy,13C,1H spin coupling constants.

ISSN:0008-4042    

DOI:10.1139/v91-142

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The course of the reactions of methoxide andtert-butoxide with 2-(2′,4′-dinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide (4) clearly shows that the C-7 electrophilic site is significantly more reactive than the C-1′ site of the substrate. The reaction pathways of these alkoxides, which differ in basicity (as a measure of nucleophilicity) and steric bulk, were followed by 400 MHz1H nuclear magnetic resonance spectroscopy. While both alkoxides lead to immediate formation of the respective C-7 anionic σ-adducts, a greater percentage of C-7 adduct formation occurs with methoxide as attacking nucleophile. Reaction with excess alkoxide results in attack at C-1′ being observed, as well. This leads to formation of metastable C-1′ σ-adducts, whose rapid decomposition results in formation of 2,4-dinitrophenyl ethers and the dinitrobenzotriazole 1-oxyanion in an overall nucleophilic displacement reaction. Under these excess conditions, methoxide also causes a faster rate of displacement than doestert-butoxide as nucleophile. These results are discussed on the basis of the basicity of the nucleophiles, the relative electrophilicity of the positions in the substrate (C-7 versus C-1′), the steric hindrance involved in attack and in the resultant C-7 and C-1′ complexes, and in terms of an activation energy/reaction coordinate profile comparing the pathways for attack at the two electrophilic sites.Keywords: anionic σ-complexes, super-electrophiles, aromatic nucleophilic substitution (SNAr).

ISSN:0008-4042    

DOI:10.1139/v91-143

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Solutions of TeO2(0.001 M) in HCl over a range of concentrations are shown to contain TeCl2(OH)2in addition to TeCl62−and TeCl4(OH)−. The hydrolysis constants for TeCl62−and TeCl4(OH)−have been determined from a reconsideration of earlier UV-visible spectrophotometric results (1)The hydrolysis constants have also been determined by quantitative Raman spectroscopy (K1 = 2.21 (± 0.16) × 104 M3;K2 = 442 ± 57 M3). The agreement betweenK2determined by the two methods is good butK1from spectrophotometry is much larger than that from Raman studies. This disagreement is attributed to ion-pairing which will be significant at the concentration at which the Raman measurements were made (c(TeO2) = 0.50 M). The hydrolysis constant for TeCl62−was also determined from the125Te NMR spectra of TeO2/HCl solutions, which consisted of one signal, indicating rapid Te exchange between all species. The hydrolysis constant, determined in this way (K1 = 1.92 (± 0.07) × 104 M3) was also low compared to that determined from spectrophotometry.Keywords: solution, equilibria, tellurium, hydrochloric acid, Raman spectroscopy,125Te NMR spectroscopy, UV–visible spectrophotometry.

ISSN:0008-4042    

DOI:10.1139/v91-144

出版商:NRC Research Press    

年代:1991

数据来源: NRC