Artificial Molecular Rotors

Design of sustainable chemical products--the example of ionic liquids.

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00723

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2+2] Photocycloaddition Reactions

The thermal decomposition of lithium-ion battery electrolytes 1.0 M LiPF 6 in one or more carbonate solvents has been investigated. Electrolytes containing diethyl carbonate (DEC), ethylene carbonate (EC), a 1:1 mixture of EC/dimethyl carbonate (DMC), and a 1:1:1 mixture EC/DMC/DEC have been investigated by multinuclear nuclear magnetic spectroscopy, gas chromatography with mass selective detection, and size exclusion chromatography. Thermal decomposition affords products including: carbon dioxide (CO 2 ), ethylene (CH 2 CH 2 ), dialkylethers (R 2 O), alkyl fluorides (RF), phosphorus oxyfluoride (OPF 3 ), fluorophosphates [OPF 2 OR, OPF(OR) 2 ], fluorophosporic acids [OPF 2 OH, OPF(OH) 2 ], and oligoethylene oxides. The mechanism of decomposition is similar in all LiPF 6 /carbonate electrolytes. Trace protic impurities lead to generation of OPF 2 OR, which autocatalytically decomposes LiPF 6 and carbonates. The presence of DEC leads to the generation of ethylene, while the presnce of EC leads to the generation of capped oligothylene oxides [OPF 2 (OCH 2 CH 2 ) n F].

https://iopscience.iop.org/article/10.1149/1.2083267/pdf

Thermal Decomposition of LiPF6-Based Electrolytes for Lithium-Ion Batteries

Controversy behind the postulation that ionic liquids (ILs) are entirely green materials emerged a few years ago. This statement is not always valid, and properties such as toxicity and chemical/thermal stability of ILs should be fully characterized to evaluate their potential use as green solvents. Therefore, in this work, the thermal and chemical decompositions of hexafluorophosphate- and tetrafluoroborate-based ILs in aqueous solutions were evaluated. The experimental conditions employed allowed the study of the possible decomposition of both anions, the effect of the cation side alkyl chain length, the influence of the pH of the aqueous solutions, as well as the temperature influence. Three experimental techniques were employed to fully characterize those anions’ stability, electrospray mass spectrometry, nuclear magnetic resonance spectroscopy, and pH measurements of the equilibrium aqueous solutions. The results noticeably indicate that it is suitable to use aqueous solutions of hexafluorophosphate-...

Hydrolysis of Tetrafluoroborate and Hexafluorophosphate Counter Ions in Imidazolium-Based Ionic Liquids†

Hydrolysis in the system LiPF6—propylene carbonate—dimethyl carbonate—H2O

1H n.m.r. spectra and semi-empirical calculations of strain energies have shown that the ground state of the toluene derivative 3 is represented by conformation a (R CH3), the α-methine proton of which eclipses one of the o-methyl groups. Accordingly, the existence of two rotamers, e.g.15E and 15Z, was demonstrated in the case of the toluenes 15, 16, 17, 18, and 19 synthesized with two unequal o- or m-substituents. The measured equilibrium ratios of rotamers (Table 2) are in good agreement with the results of the calculations for 15 and 16. - The free enthalpies of activation ΔGmath image for rotation about the Cαaryl bond vary from < 7.5 to 15 kcal/mole (Tables 1 and 2). Barriers of this kind were reproduced with sufficient accuracy by calculations for 3, 15, and 16 if the Cαaryl bond length and the bond angles were assumed to be flexible, i.e., if they were optimized for each rotational arrangement. The transition state turned out to be a conformation of type d, the CαH bond of which is arranged perpendicular to the benzene ring; potential energy curves for Cαaryl rotation are given in Fig. 3 and 4. Calculations presupposing a rigid molecular geometry erroneously result in conformation c as the transition state and yield barriers which are much higher than the measured ones.

Protonenresonanz-Untersuchungen zur inneren Rotation, VIII. Konformationsanalyse α.α.o.o′-tetrasubstituierter Toluole mittels magnetischer Kernresonanz und halbempirischer Energieberechnung

13C chemical shifts and 31P13C spin–spin coupling constants are reported for 10 alkyl-, 20 benzyl- and 3 (naphthylmethyl)-phosphonates. While in saturated aliphatic chains P–C couplings over more than four bonds cannot be resolved, couplings over up to seven bonds are observed in the benzyl type systems. Conformational and substituent effects on J(PC) are studied and discussed. nJ(PF) (n = 4, 5, 6) are reported for the isomeric (fluorobenzyl)phosphonates and nJ(PP) (n = 5, 6, 7) were obtained from the 13C satellites in the 31P n.m.r. spectra of the isomeric diphosphonates, C6H4[CH2P(O)(OEt)2]2. Comparison of those 13C absorptions of the latter, which represent the X parts of ABX or AA′X spin systems, with the spectra of the corresponding (methylbenzyl)phosphonates, CH3C6H4CH2P(O)(OEt)2, yielded the relative signs of nJ(PC) (n = 2–6).

13C n.m.r. spectroscopy of diethyl alkyl- and benzyl-phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds

In den 13C-NMR-Spektren von 1-Naphthol (1), 2-Naphthol (2), 1-Methoxynaphthalin (4), 2-Methoxynaphthalin (5), 1,5-Naphthalindiol (7), 2,6-Naphthalindiol (8) und 2,7-Naphthalindiol (9) in [D6]Aceton- und CDCl3-Losung konnten samtliche Signale zugeordnet werden Hierbei erwiesen sich die Aufnahme protonengekoppelter Spektren sowie selektive Entkopplung der Protonen als wertvolle Hilfsmittel Die verringerte Anzahl der Signale und die strikte Additiviat der Substituenteneffekte auf die chemischen Verschiebungen in den symmetrischen Diolen sichert die Signalzuordnung bei den Monohydroxyderivaten zusatzlich ab Man beobachtet starke Substituenteneffekte, die sich bis uber die maximal mogliche Anzahl von Bindungen bemerkbar machen und sich anhand der kanonischen Formen deuten lassen, die am starksten zum Resonanz-hybrid beitragen



13CNMR Spectroscoopy of Polycyclic Aromatics, I Naphthols, Naphthalenediols, and Methoxynaphthalenes Complete Assignment of the 13CNMR Spectra and Investigation of Substituent Effect on chemical Shifts



In the 13C nmr spectra of 1-naphthol (1), 2-naphthol (2), 1-methoxynaphthalene (4), 2-methoxynaphthalene (5), 1,5-naphthalenediol (7), 2,6-naphthalenediol (8), and 2,7-naphthalenediol (9) in [D6]acetone and CDCl3 all signals have been assigned Proton-coupled and selectively decoupled spectra proved to be valuable aids The lower number of signals and the strict additivity of substituent effects upon the chemical shifts in the symmetrical diols further confirmed the assignments in the monohydroxy derivatives Strong substituent effects over the maximum possible number of bonds were observed and could be rationalized by considering those canonical structures that contribute mostly to the resonance hybrid

13C‐NMR‐Spektroskopie an polycyclischen Aromaten, I. Naphthole, Naphthalindiole und Monomethoxynaphthaline. Vollständige Zuordnung der 13C‐NMR‐Spektren und Untersuchung der Substituenteneffekte auf die chemischen Verschiebungen

Ludger Ernst

Papers

Hydrolysis in the system LiPF6—propylene carbonate—dimethyl carbonate—H2O

Protonenresonanz-Untersuchungen zur inneren Rotation, VIII. Konformationsanalyse α.α.o.o′-tetrasubstituierter Toluole mittels magnetischer Kernresonanz und halbempirischer Energieberechnung

13C n.m.r. spectroscopy of diethyl alkyl- and benzyl-phosphonates. A study of phosphorus–carbon spin–spin coupling constants over one to seven bonds

13C‐NMR‐Spektroskopie an polycyclischen Aromaten, I. Naphthole, Naphthalindiole und Monomethoxynaphthaline. Vollständige Zuordnung der 13C‐NMR‐Spektren und Untersuchung der Substituenteneffekte auf die chemischen Verschiebungen

A new quantitative description of the distance dependence of through-space19f, 19f spin-spin coupling