Role of pK a in establishing the crystal structures of six hydrogen-bonded compounds of 4-methylquinoline with different isomers of chloro- and nitro-substituted benzoic acids

The structures of the six hydrogen-bonded 1:1 compounds of 4-methylquinoline (C10H9N) with chloro- and nitro-substituted benzoic acids (C7H4ClNO4), namely, 4-methylquinolinium 2-chloro-4-nitrobenzoate, C10H10N+·C7H3ClNO4 −, (I), 4-methylquinoline–2-chloro-5-nitrobenzoic acid (1/1), C10H9N·C7H4ClNO4, (II), 4-methylquinolinium 2-chloro-6-nitrobenzoate, C10H9.63N0.63+·C7H3.37ClNO4 0.63−, (III), 4-methylquinolinium 3-chloro-2-nitrobenzoate, C10H9.54N0.54+·C7H3.46ClNO4 0.54−, (IV), 4-methylquinolinium 4-chloro-2-nitrobenzoate, C10H10N+·C7H3ClNO4 −, (V), and 4-methylquinolinium 5-chloro-2-nitrobenzoate, C10H10N+·C7H3ClNO4 −, have been determined at 185–190 K. In each compound, the acid and base molecules are linked by a short hydrogen bond between a carboxy (or carboxylate) O atom and an N atom of the base. The O...N distances are 2.5652 (14), 2.556 (3), 2.5485 (13), 2.5364 (13), 2.5568 (13) and 2.5252 (11) Å, respectively, for compounds (I)–(VI). In the hydrogen-bonded acid–base units of (III) and (IV), the H atoms are each disordered over two positions with O site:N site occupancies of 0.37 (3):0.63 (3) and 0.46 (3):0.54 (4), respectively, for (III) and (IV). The H atoms in the hydrogen-bonded units of (I), (V) and (VI) are located at the N-atom site, while the H atom in (II) is located at the O-atom site. In all the crystals of (I)–(VI), π–π stacking interactions between the quinoline ring systems and C—H...O hydrogen bonds are observed. Similar layer structures are constructed in (IV)–(VI) through these interactions together with π–π interactions between the benzene rings of the adjacent acid molecules. A short Cl...Cl contact and an N—O...π interaction are present in (I), while a C—H...Cl hydrogen bond and a π–π interaction between the benzene ring of the acid molecule and the quinoline ring system in (II), and a C—H...π interaction in (III) are observed. Hirshfeld surfaces for the title compounds mapped over d norm and shape index were generated to visualize the weak intermolecular interactions.

INFLUENCE OF SUBSTITUTES ON THE RATE OF THE REACTION OF ORTHOSUBSTITUTED BENZOIC ACIDS WTH ANILINE, CATALYZED BY POLYBUTOXYTITANATES

The polybutoxytitanates catalysis of aniline acylation by orthosubstituted benzoic acids leads to the production of substituted benzanilides. Catalytic rate constants of the second order reaction (the first with respect to aniline and ortho-substituted benzoic acid; boiling ortho=xylene, 145°C) correlate well according to the Hammett and Bronsted equations with straight line segments with ρ=1.93 and α=0.66, in contrast to the reaction of aniline with meta- and parasubstituted benzoic acids and substituted anilines with benzoic acid. This dependence drops out 2=nitrobenzoic and 1=naphthoic acids, which have relatively low reactivity and the greatest steric hindrances both for nucleophilic attack by aniline and for possible coordination with catalytically active centers of the corresponding ortho-substituted titanium polybutoxybenzoates formed in situ. Based on these data, the previously proposed mechanism of bifunctional catalysis due to titanium polybutoxybenzoates and their complexes with meta- and parasubstitutedbenzanilides was supplemented by the possibility of the steric inhibition of reaction by the most bulky substituents and chelate structures formation of orthosubstituted benzoic acids and their anilides with individual titanium atoms of the catalyst, as well as the simulta­neous H-bonding of the amino group hydrogen atoms of aniline, which leads to its activation to a nucleophilic attack, with a carbonyl group and an orthopositioned substituent of the orthobenzoate ligand in the coordination sphere of titanium. Taking into account such chelation and steric barriers, as well as inhibition of acid catalysis due to the formation of the imide form of anilides, containing electron-withdrawing substituents, the equations for the rate constants of the catalytic reaction of ortho-substituted benzoic acids with aniline are derived, corresponding to the experimentally obtained Hammett dependence.

A Web Tool for Calculating Substituent Descriptors Compatible with Hammett Sigma Constants

<p>Electron donating or accepting power of organic substituents is an important parameter affecting many properties of parent molecules, most notably their reactivity and pKa of ionizable groups. These substituent properties are usually described by Hammett sigma constants obtained by measuring ionization of substituted benzoic acids. Although values of these constants have been measured for the most common functional groups, data for many important substituents are not available. Some time ago we reported a method to calculate substituent descriptors compatible with Hammett sigma constants using quantum chemically derived parameters. The present publication revisits the older study by applying more sophisticated methodology and a larger training data set, as well as introduces a free web tool allowing to calculate substituent descriptors compatible with Hammett sigma constants available at <a href="https://bitly.com/getsigmas">https://bitly.com/getsigmas</a>.</p><div><br></div>

A Web Tool for Calculating Substituent Descriptors Compatible with Hammett Sigma Constants

<p>Electron donating or accepting power of organic substituents is an important parameter affecting many properties of parent molecules, most notably their reactivity and pKa of ionizable groups. These substituent properties are usually described by Hammett sigma constants obtained by measuring ionization of substituted benzoic acids. Although values of these constants have been measured for the most common functional groups, data for many important substituents are not available. Some time ago we reported a method to calculate substituent descriptors compatible with Hammett sigma constants using quantum chemically derived parameters. The present publication revisits the older study by applying more sophisticated methodology and a larger training data set, as well as introduces a free web tool allowing to calculate substituent descriptors compatible with Hammett sigma constants available at <a href="https://bitly.com/getsigmas">https://bitly.com/getsigmas</a>.</p><div><br></div>

Synthesis of Benzo-Fused Cyclic Compounds via Rhodium-Catalyzed Decarboxylative Coupling of Aromatic Carboxylic Acids with Alkynes

The decarboxylative coupling of diversely substituted benzoic acids with internal alkynes proceeds smoothly in the presence of a [RhCl(cod)]2/1,2,3,4-tetraphenyl-1,3-cyclopentadiene catalyst system to selectively produce highly substituted naphthalene derivatives. The catalyst system is applicable to constructing anthracene and benzo­[c]thiophene frameworks through reactions of naphthoic and thiophene-2-carboxylic acids, respectively.

Can molecular flexibility control crystallization? The case of para substituted benzoic acids

Little is known about the relationship between the kinetic process of nucleation and the molecular and crystal structures of a crystallizing solute. Here we compare the behaviour of a series of benzoic acids with a focus on conformational effects.

Oxidative C-H Acyloxylation of Acetone with Carboxylic Acids under Iodine Catalysis

Iodine catalyzed oxidative C(sp3)-H acyloxylation of acetone with carboxylic acids has been developed. The method employs an iodide as catalyst and sodium chlorite as oxidant. Substituted benzoic acids, naphthoic acids and hetero-aromatic carboxylic acids can be used, and 2-oxopropyl carboxylates are obtained with good to excellent yields.

Structural Aspects of the Ortho Chloro- and Fluoro- Substituted Benzoic Acids: Implications on Chemical Properties

This article presents a detailed comprehensive investigation of the ortho fluoro- and chloro- substituted benzoic acids both, as isolated molecules and in the crystalline phase. Quantum chemical calculations performed within the density functional theory (DFT) formalism are used to investigate the potential energy landscapes of the molecules, taking into special consideration the effects of the interactions between the carboxylic group and the ortho halogen substituents, as well as the nature of these later on the structure and properties of the investigated systems. The structures of the relevant conformers of the molecules are discussed in comparative terms, and used to rationalize experimental data obtained for the compounds in the gas phase and isolated in low-temperature inert matrices. The UV-induced photofragmentation reactions of two of the compounds isolated in cryogenic inert matrices were studied as illustrative cases. The structures of the crystals reported previously in the literature are revisited and discussed also in a comparative basis. Particular emphasis is given to the analysis of the intermolecular interactions in the different crystals, using Hirshfeld surface analysis, the CE-B3LYP energy decomposition model and the HOMA index, and to their correlation with thermodynamic data.