Acid-base equilibria in nonpolar media. 3. Expanding the spectrophotometric acidity scale in heptane

The UV-vis spectrophotometric ion-pair acidity scale in heptane has been significantly expanded: it includes now 21 bulky CH and NH indicator acids and spans for about 10 pKip units. The phosphazene base t-Bu-P4 was used for deprotonating. The correlations between acidities in heptane versus gas-phase acidities or acidities in DMSO or 1,2-dimethoxyethane have been made for some compounds. It was demonstrated that the substituent effects on the acidity of the studied CH acids are attenuated ca. 1.24 times when the gas phase is substituted for the nonpolar solvent, heptane. In its turn, for the series of NH acids, the latter is found to be a somewhat more differentiating solvent than DMSO.     

Lithium-cation and proton affinities of sulfoxides and sulfones: A fourier transform ion cyclotron resonance study

The kinetic method was used for the quantitative determination of lithium-cation affinities by Fourier transform ion cyclotron resonance. This method was applied to a series of XYSO and XYSO₂ compounds. Proton basicities of the SO and SO₂ compounds were also determined. When comparison is made between Li⁺ basicities and proton basicities, a linear regression encompassing XYSO and XYSO₂ families suggests that Li⁺ may be bonded in a similar way to the SO and SO₂ moieties, that is, to only one oxygen on the latter. PM3 calculations support this hypothesis.     

Gas‐phase acidity of bis[(perfluoroalkyl)sulfonyl]imides. Effects of the perfluoroalkyl group on the acidity

The gas‐phase acidity (GA) values were determined for a number of perfluoroalkyl‐substituted sulfonylimides by measuring proton‐transfer equilibria using a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The GA scale below 286.5 kcal mol^?1 for (CF₃SO₂)₂NH was extended and partially revised. The GA value of (C₄F₉SO₂)₂NH which is currently the strongest acid was revised from 284.1 to 278.6 kcal mol^?1. The effect of fluorine atoms on the acidity of perfluoroalkyl‐substituted sulfonylimides was described with the following model where N_(α), N_(β), N_(γ), and N_(δ) are the numbers of fluorine atoms at α, β, γ, and δ position in R_fSO₂ (R_f = perfluoroalkyl group), respectively. This correlation indicates that the electron‐withdrawing ability of the R_fSO₂ group can be described in terms of the number of fluorine atoms in the perfluoroalkyl group corrected by taking into account their positions. Copyright © 2014 John Wiley & Sons, Ltd.     

New Method for Synthesis of Methacrylate-Type Polymerizable Ionic Liquids

A new method for the synthesis of polymerizable ionic liquids bearing a methacrylate moiety was developed with the aim to avoid premature polymerization of synthesized compounds. Spacer length between the imidazolium cation and the polymerizable functional group varied from 2 to 10 carbon atoms. Different 1-(n-hydroxyalkyl)-3-methylimidazolium bromides and 1-[n-(methacryloyloxy)-alkyl]-3-methylimidazolium bromides were obtained with very good yields (more than 90%).

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

Rotor–stator contact dynamics using a non-ideal drive—Theoretical and experimental aspects

The possible contact between rotor and stator is considered a serious malfunction that may lead to catastrophic failure. Rotor rub is seen as a secondary phenomenon caused by a primary source, i.e. sudden mass unbalance, instabilities generated by aerodynamic and hydrodynamic forces in seals and bearings among others. The contact event gives rise to normal and friction forces exerted on the rotor at impact events. The friction force plays a significant role by transferring some rotational energy of the rotor to lateral motion. A mathematical model has been developed to capture this for a conventional backup annular guide setup. It is reasonable to superpose an impact condition to the rub, where the rotor spin energy can be fully transformed into rotor lateral movements. Using a nonideal drive, i.e. an electric motor without any kind of velocity feedback control, it is even possible to stop the rotor spin under rubbing conditions. All the rotational energy will be transformed in a kind of “self-excited” rotor lateral vibration with repeated impacts against the housing. This paper studies the impact motion of a rotor impacting a conventional backup annular guide for the case of dry and lubricated inner surface of the guide. For the dry surface case, the experimental and numerical analysis shows that the rotational energy is fully transformed into lateral motion and the rotor spin is stopped. Based on this study this paper proposes a new unconventional backup bearing design in order to reduce the rub related severity in friction and center the rotor at impact events. The analysis shows that the rotor at impacts is forced to the center of the backup bearing and the lateral motion is mitigated. As a result of this, the rotor spin is kept constant.     

Experimental bifurcation analysis of an impact oscillator—Determining stability

We propose and investigate three different methods for assessing stability of dynamical equilibrium states during experimental bifurcation analysis, using a control-based continuation method. The idea is to modify or turn off the control at an equilibrium state and study the resulting behavior. As a proof of concept the three methods are successfully implemented and tested for a harmonically forced impact oscillator with a hardening spring nonlinearity, and controlled by electromagnetic actuators. We show that under certain conditions it is possible to quantify the instability in terms of finite-time Lyapunov exponents. As a special case we study an isolated branch in the bifurcation diagram brought into existence by a 1:3 subharmonic resonance. On this isola it is only possible to determine stability using one of the three methods, which is due to the fact that only this method guarantees that the equilibrium state can be restored after measuring stability.     

Theoretical study of structure and basicity of some alkali metal oxides,hydroxides, and amides

Ab initio (TZV *, SBK *, and 3–21G * or 6–31G * basis sets) calculations were performed to predict the geometries and gas-phase proton affinities of Li₂O, LiOH, LiNH₂, Na₂O, NaOH, NaNH₂, K₂O, KOH, and KNH₂. © 1994 John Wiley & Sons, Inc.     

Acidity of di- and triprotected hydrazine derivatives in dimethyl sulfoxide and aspects of their alkylation

The pK(a) values in DMSO for 22 di- and triprotected hydrazine NH acids and two monosubstituted hydrazines have been determined using potentiometric titration. The results of density functional theory calculations at the B3LYP/6-311+G level of gas-phase acidities of a representative selection of mono-, di-, and trisubstituted hydrazines are compared with both the relevant published and novel experimental titration data. In the course of this work, a rough estimation of the pK(a) value of hydrazine in DMSO (ca. 38.0) has been deduced. For typical triprotected compounds of this kind containing moderately electron-withdrawing carbamate and imidodicarbonate or arenesulfonylcarbamate functions the pK(a) values fall in the range 15.1-17.3, whereas for N,N'-diprotected hydrazines with a carbamate and an aromatic sulfonyl group the corresponding values are 12.7-14.5. Several of these triprotected derivatives have recently been applied preparatively in stepwise synthesis of substituted hydrazines using alkyl halides as electrophiles in the presence of a phase transfer catalyst, and a few of them, with varying success, have been examined in model experiments with benzyl alcohol, triphenylphosphine, and diethyl azodicarboxylate in the Mitsunobu reaction. The dependence of the reactivity on the intrinsic acidity of the hydrazines in this reaction is highlighted. Furthermore, the regioselective alkylation of an N,N'-diprotected hydrazine can be rationalized on the basis of the presented data.     

A New Class of Organosuperbases,N‐Alkyl‐ and N‐Aryl‐1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐ylidene Amines: Synthesis,Structure, pKBH+ Measurements,and Properties

A series of stable organosuperbases, N‐alkyl‐ and N‐aryl‐1,3‐dialkyl‐4,5‐dimethylimidazol‐2‐ylidene amines, were efficiently synthesized from N,N′‐dialkylthioureas and 3‐hydroxy‐2‐butanone and their basicities were measured in acetonitrile. The derivatives with tert‐alkyl groups on the imino nitrogen were found to be more basic than the tBu P₁ (pyrr) phosphazene base in acetonitrile. The origin of the high basicity of these compounds is discussed. In acetonitrile and in the gas phase, the basicity of the alkylimino derivatives depends on the size of the substituent at the imino group, which influences the degree of aromatization of the imidazole ring, as measured by ¹³C NMR chemical shifts or by the calculated ΔNICS(1) aromaticity parameters, as well as on solvation effects. If a wider range of imino‐substituents, including electron‐acceptor substituents, is treated in the analysis then the influence of aromatization is less predominant and the gas‐phase basicity becomes more dependent on the field‐inductive effect, polarizability, and resonance effects of the substituent.