J. Appl. Cryst.の発刊に際して

An empirical conversion method (ECM) that transforms pKa values of arbitrary organic compounds from one solvent to the other is introduced. We demonstrate the method’s usefulness and performance on pKa conversions involving water and organic solvents acetonitrile (MeCN), dimethyl sulfoxide (Me2SO), and methanol (MeOH). We focus on the pKa conversion from the known reference value in water to the other three organic solvents, although such a conversion can also be performed between any pair of the considered solvents. The ECM works with an additive parameter that is specific to a solvent and a molecular family (essentially characterized by a functional group that is titrated). We formally show that the method can be formulated with a single additive parameter, and that the extra multiplicative parameter used in other works is not required. The values of the additive parameter are determined from known pKa data, and their interpretation is provided on the basis of physicochemical concepts. The data set of k...

Empirical Conversion of pKa Values between Different Solvents and Interpretation of the Parameters: Application to Water, Acetonitrile, Dimethyl Sulfoxide, and Methanol

In the last decade a certain number of new cyclobutane and cyclobutanone synthesis and functionalization protocols have been published. Organo- and biocatalyzed eco-friendly approaches to cyclobutane-containing molecules have been developed with interesting results. Also, successful new total synthesis of bioactive compounds and drugs have been recently reported where a four membered ring represented the key intermediate. Therefore, the rising interest in this field represents a great point of discussion for the scientific community, disclosing the synthetic potential of strained four membered ring carbocyclic compounds. Herein we report a critical survey on the literature concerning the enantiocontrolled synthesis and functionalization of cyclobutane derivatives, with particular attention to metal-free, low impact methodologies, published during the period 2000-2013.

https://www.mdpi.com/1420-3049/18/12/15541/pdf

Stereocontrolled synthesis and functionalization of cyclobutanes and cyclobutanones.

Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion–π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π-acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π-acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α-protons in the 1H NMR spectra. The reactivity of these protons on π-acidic surfaces is measured by hydrogen–deuterium (H–D) exchange for 11 different examples, excluding controls. The velocity of H–D exchange increases with π acidity (NDI core substituents: SO2R>SOR>H>OR>OR/NR2>SR>NR2). The H–D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11–13 atoms). Most importantly, H–D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)-macrocycle is reported). For maximal π acidity, transition-state stabilizations up to −18.8 kJ mol−1 are obtained for H–D exchange. The Bronsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pKa=10.9 calculates to a ΔpKa=−5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as “impossible” in biology, the found enolate–π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven-component π-acidity gradient over almost 1 eV demonstrates quantitatively that such important anion–π activities can be expected only from strong enough π acids.

/pdf/enolate-stabilization-by-anion-p-interactions-deuterium-51xy9ve99l.pdf

Enolate Stabilization by Anion–π Interactions: Deuterium Exchange in Malonate Dilactones on π‐Acidic Surfaces

The paper shows how the direct current ionic conductivity (σDC) and the static dielectric permittivity (es) reveal themselves in the complex impedance, the electric modulus, and the conductance of molecular liquids when the frequency of the electric stimulus is much lower than that corresponding to the dipolar reorientational relaxation of the liquid under investigation. It was shown that, in such static dielectric conditions, one observes the relaxational behavior of the impedance and the electric modulus, both of the Debye-type and of the same relaxation time, depending on σDC and es values. The discussion is illustrated with the experimental electric spectra of liquid cyclobutanone recorded in the frequency region from 500 Hz to 5 MHz and in the temperature range from 243 to 313 K.

Electric Relaxational Effects Induced by Ionic Conductivity in Dielectric Materials

The induction of strain in carbocycles, thereby increasing the amount of s-character in the C−H bonds and the acidity of these protons, has been probed with regard to its effect on the rate constan...

Determination of the pKa of cyclobutanone: Brønsted correlation of the general base-catalyzed enolization in aqueous solution and the effect of ring strain.

The title compound, C16H22N2O3, was synthesized during the course of a study on (1R,2S)-norephedrine-derived 1,3,4-oxadiazinan-2-ones. The conformation adopted by the isopropyl group is pseudo-axial relative to the oxadiazinan core. The allylic strain contributes to this conformational arrangement.

https://journals.iucr.org/e/issues/2009/07/00/zl2203/zl2203.pdf

Dishant Tailor

Papers

Determination of the pKa of cyclobutanone: Brønsted correlation of the general base-catalyzed enolization in aqueous solution and the effect of ring strain.

(5R,6S)-4-Isopropyl-5-methyl-6-phenyl-3-propanoyl-2H-1,3,4-oxadiazinan-2-one