Regioselective control of allyllithiums of some heterocycles: α vs γ condensation with aldehydes.

A procedure for directing the condensation of allyllithiums of benzothiazole, benzoxazole and pyrimidine such as 2 with aldehydes to the α or γ position is described. Erythro diasteroselection is observed in the α regioisomers.     

Structure and photochemistry of “bridged” bifunctional radical cations: Amidoesters vs. amides

Structure and properties of the radical cations of “bridged” amidoesters (functional groups separated by 0–4 methylene groups and the corresponding dimethyl-substituted amides) were investigated by EPR, optical absorption spectroscopy and DFT calculations. The EPR spectra and thermal reactions of these species are similar. Meanwhile, for amidoesters with 2–4 methylene groups, the methylene “bridge” is involved in photochemistry, which can be explained by specific conformation of amidoester radical cations determined by interaction between the functional groups.     

Infrared bandshapes of intramolecularly H-bonded systems—III. Vibrational dephasing of vs (OH) in 2,6-dichlorophenol

The shape of the v_s (OH) absorption band of intramolecularly H-bonded 2,6-dichlorophenol was measured in a series of solvents of increasing polarity and quantitatively analyzed. A distinct dependence of band positions, shape parameters, band moments, integrated intensities, correlation functions and correlation times on the polarity of solvent has been found. Vibrational dephasing due to dipole—dipole interactions seems to be an important relaxation pathway determining the bandshape in the studied systems.     

Abstraction of β-hydrogen vs. alkyl groups in reactions of dialkylzinc compounds and bis(oxazolinyl)borane

An ambiphilic bis(oxazolinyl)borane proligand and zinc dialkyls react via alkyl group transfer or β-hydrogen abstraction. The latter process is favored by formation of a bis(oxazolinyl)borane-zinc adduct that positions a β-hydrogen in the proximity of the Lewis acid center.     

Determination of oil–water partition coefficients of polar compounds: silicone membrane equilibrator vs. SPME passive sampler

Experimental determination of oil-water partition coefficients often poses difficulties associated with emulsion formation. The aim of this work was to find an appropriate technique for determination of oil–water partition coefficients of polar, nonvolatile compounds. Two different methods were tested. The first method used a “silicone membrane equilibrator.” For the second method, solid-phase microextraction (SPME) fibers with a polyacrylate (PA) coating were used as a passive sampler. With both methods, oil–water partition coefficients for 14 compounds with polar functional groups were determined at 37 °C with good repeatability (standard deviation 0.11 log units or lower). The partition coefficients determined with the silicone membrane equilibrator method ranged from 0.50 to 3.49 log units. The oil–water partition coefficients obtained with the PA-SPME passive sampling approach were significantly higher than those obtained with the silicone membrane equilibrator method for nine of 14 compounds. The differences were up to 0.39 log units (i.e., a factor of 2.5). Additional experiments suggested that this difference occurred because the sorption properties of the PA fibers used were influenced by the surrounding phase, e.g., through swelling of the polymer phase. Therefore, the SPME passive sampling method using PA fibers seems to be less reliable, whereas the silicone membrane equilibrator method was found to be a convenient technique for the determination of oil–water partitioning.     

Broadband dielectric spectroscopic studies of molecular motions in a Nafion® membrane vs. annealing time and temperature

The dynamics of macromolecular motions as coupled to proton migration in annealed Nafion® membranes were explored at temperatures above 100 °C using broadband dielectric spectroscopy. Loss permittivity vs. frequency spectra of both β and α relaxations showed increased relaxation times with annealing which was rationalized in terms of water de-sorption and diminished free volume. The α relaxation time increases with increased annealing temperature. A parameter N reflecting connectedness of charge hopping pathways was extracted and indicated that the conductivity network accumulates more charge traps, presumably due to free volume decrease, with increased annealing time. Conductivity increases with increased annealing time at all temperatures despite the decrease in N; this suggests a change in the nature of proton hopping on annealing at high temperatures to be between sulfonic acid groups rather than by hopping across H₂OH⁺OH₂ bonds.     

One-bond CC spin—spin coupling constants in derivatives of benzene. Non-linearity of 1J(CC) vs substituent electronegativity

A set of one-bond CC coupling constants has been determined for mono- and disubstituted benzenes. Large ¹J(CC) values have been found within the benzene rings bearing highly electronegative substituents such as halogens, methoxy and nitro groups and small values for those with electropositive substituents. The total range of ¹J(CC) couplings observed in our work is larger than 50 Hz. These large variations of CC spin—spin couplings are interpreted in terms of Fermi-contact contributions and the redistribution of s-electrons within a CC bond under influence of substituents. Contrary to some previous findings the data obtained in the present work indicate that the relationship between ¹J(CC) and the substituent electronegativity is not linear.     

Chaotrope vs. kosmotrope: which one has lower friction?

We examine the frictional properties of zwitterionic surfaces and explore whether chaotropic or kosmotropic charged groups are preferred to achieve lower friction. Self-assembled monolayers of carboxybetaine (CB-SAMs) and sulfurbetaine (SB-SAMs) are used as model surfaces as they contain the same positively charged group, but different negatively charged ones. The negatively charged groups are kosmotropic carboxylates in the CB-SAM surfaces and chaotropic sulfonate groups in the SB-SAM surfaces, respectively. The results show that the friction of the SB-SAM surfaces is even lower than that of the CB-SAM surfaces although both surfaces have low friction. This suggests that chaotropic charged groups are better in reducing friction than kosmotropic groups. The lower friction of the SB-SAM surfaces over the CB-SAM can be explained by the higher mobility of water near the SB-SAM surfaces, as shown in the survival autocorrelation function and the dipole autocorrelation function of hydration water molecules.     

Chin.J.Chem.设立"NHU-CJC Innovation Award"

新和成控股集团有限公司着力于中国学术期刊的大发展,提升我国期刊的国际影响力,与中国科学院上海有机化学研究所于2018年1月签署协议,自2018年至2022年,每年捐赠人民币二十万元,对投稿给Chin.J.Chem.原则性非常强的工作,由主编或副主编提名,经主编和副主编全体投票,获2/3同意,授予“新和成《中国化学》创新奖”(NHU-CJC Innovation Award),每位作者均将获得证书和奖金,相关工作将在Breaking Report栏目发表。     

Chin.J.Chem.设立"NHU-CJC Innovation Award"

正新和成控股集团有限公司着力于中国学术期刊的大发展,提升我国期刊的国际影响力,与中国科学院上海有机化学研究所于2018年1月签署协议,自2018年至2022年,每年捐赠人民币二十万元,对投稿给Chin.J.Chem.原创性非常强的工作,由主编或副主编提名,经主编和副主编全体投票,获2/3同意,授予"新和成《中国化学》创新     

“Demonstration” vs. “designation” of measurement competence: the need to link accreditation to metrology

Formal acceptance of the results of chemical laboratories is increasingly organized through a) accreditation of measuring laboratories nationally and b) mutual recognition of accreditation internationally (through formal Multilateral Recognition Agreements, MRAs). However, real comparability of results of measurements is realized by using common (internationally agreed) measurement scales which make these results traceable to this scale, i.e. “traceable” to the same (internationally agreed) value of the unit of that scale. In addition, the criterion against which the evaluation is done, should be “external” to the measurement laboratories which are being evaluated. This is realized in IRMM’s International Measurement Evaluation Programme (IMEP) where evaluation is performed against values which are anchored using “metrology”, the science of measurement with its own rules, which offers a sound foundation for measurement in all scientific disciplines. It is argued in this paper that the demonstration of measurement capability against values on such scales provides a result-oriented rather than a procedure-oriented evaluation. Thus, competence can be “demonstrated” rather than just “designated” and this can be shown to both customers and regulators. It inspires more confidence.     

Chin.J.Chem.设立"NHU-CJC Innovation Award"

<正>新和成控股集团有限公司着力于中国学术期刊的大发展,提升我国期刊的国际影响力,与中国科学院上海有机化学研究所于2018年1月签署协议,自2018年至2022年,每年捐赠人民币二十万元,对投稿给Chin.J.Chem.原创性非常强的工作,由主编或副主编提名,经主编和副主编全体投票,获2/3同意,授予"新和成《中国化学》创新奖"(NHU-CJC Innovation Award),每位作者均将获得证书和奖金,相关工作将在Breaking Report栏目发表。     

Chin.J.Chem.设立"NHU-CJC Innovation Award"

<正>新和成控股集团有限公司着力于中国学术期刊的大发展,提升我国期刊的国际影响力,与中国科学院上海有机化学研究所于2018年1月签署协议,自2018年至2022年,每年捐赠人民币二十万元,对投稿给Chin.J.Chem.原创性非常强的工作,由主编或副主编提名,经主编和副主编全体投票,获2/3同意,授予"新和成《中国化学》创新奖"(NHU-CJC Innovation Award),每位作者均将获得证书和奖金,相关工作将在Breaking Report栏目发表。     

Review of the heats of chemisorption of gases at metals in the context of the problem of ‘Heterogeneous’ <Emphasis Type="Italic">vs.</Emphasis> ‘Homogeneous’ catalytic surfaces

A critical review of available data on the heats of chemisorption of gases at metals is given. The effect of upward technical and procedural trends on measured results is demonstrated. The results for surfaces approached to their states occurring in catalytic processes are accentuated. Several tens of chemisorbent/gas systems are considered; a number of the results are confirmed by several independent measurements. The coverage-independence of heats of chemisorption for powders, supported catalysts, components of multi-component catalysts, and films is demonstrated; the better the techniques and procedures, the closer to zero the angle between the heat-coverage function and the abscissa. The principal conclusion on surface homogeneity of stabilized surfaces is made.     

Sulfonyl vs. carbonyl group: which is the more electron-withdrawing?

Unexpectedly high reactivity of nitrogenated aromatics protected as amides or carbamates, when compared to sulfonamides, can be explained by a decrease of the aromaticity due to a greater ability of the carbon-centered groups to achieve delocalisation of the nitrogen lone pair, resulting in stronger global withdrawing effects.     

Neutral C–H bond vs. electron pair of N(sp~2): A binding site effect study of macrocycle anion receptor

To evaluate the effect of neutral C–H bond or electron pair of nitrogen atom with sp2hybridization(N(sp2)) involving into the same chemical environment for anion binding, two analogous tetracationic imidazolium macrocycles, namely cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine) [2](1,3-dimethylenebenzene)(14+), and cyclo[2](2,6-bis-(1H-imidazol-1-yl)pyridine)[2](2,6-di methylenepyridine)(24+)were studied in detail as small inorganic anion receptors. The guest anions with different shapes are Cl,N3, NO3, and H2PO4. The host–guest interactions were characterized via1 H NMR spectroscopy,electrospray ionization mass spectrometry(ESI-MS) and single crystal X-ray crystallography. The results implied that macrocyclic hosts with similar backbone but two distinct binding sites(14+with neutral C–H vs. 24+with N(sp2)) vary markedly in their response to anions, including the binding modes and association constants. The finding will serve to the construction of new anion receptors, even improve insights into the anion binding process in biology.