P.I. Demyanov

A Bond Path and an Attractive Ehrenfest Force Do Not Necessarily Indicate Bonding Interactions: Case Study on M2X2 (M=Li, Na, K; X=H, OH, F, Cl)

Interactions in dimers of model alkali metal derivatives M(2)X(2) (M = Li or Na or K; X = H or F, Cl, OH) are studied in the frame of the quantum theory of atoms in molecules (QTAIM) using the interacting quantum atoms approach (IQA). Contrary to opinion prevalent in QTAIM studies, the interaction between two anions linked by a bond path is demonstrated to be strongly repulsive. One may therefore say that a bond path does not necessarily indicate bonding interactions. The interactions between two anions or two cations that are not linked by a bond path are also strongly repulsive. The repulsive anion-anion and cation-cation interactions are outweighed by much stronger attractive anion-cation interactions, and the model molecules are therefore in a stable state. The attractive Ehrenfest forces (calculated in the frame of the QTAIM) acting across interatomic surfaces shared by anions in the dimers do not reflect the repulsive interactions between anions. Probable reasons of this disagreement are discussed. The force exerted on the nucleus and the electrons of a particular atom by the nucleus and the electrons of any another atom in question is proposed. It is assumed that this force unambiguously exposes whether basins of two atoms are attracted or repelled by each other in a polyatomic molecule.

Structures of lithium salts of substituted 1-phenylpropynes: 13C NMR and MNDO study

Abstract 13C NMR spectroscopy has been used to study the structure of ambident carbanions in contact (CIP) and solvent-separated (SSIP) ion pairs of lithium salts of substituted 1-phenylpropynes. It was shown that the structures of carbanions in SSIP are close to the propargylic type, whereas, with the decrease in delocalizing ability of substituents at the propargylic centre, their structure shifts to the allenylic type, in fair agreement with theoretical predictions by the MNDO semi-empirical method. In CIP, the structures of carbanions are progressively changed from near-to-propargylic to allenylic with decrease of delocalizing ability of the substituents.

Forced Bonding and QTAIM Deficiencies: A Case Study of the Nature of Interactions in He@Adamantane and the Origin of the High Metastability

Calculations within the framework of the interacting quantum atoms (IQA) approach have shown that the interactions of the helium atom with both tertiary, tC, and secondary, sC, carbon atoms in the metastable He@adamantane (He@adam) endohedral complex are bonding in nature, whereas the earlier study performed within the framework of Baders quantum theory of atoms in molecules (QTAIM) revealed that only He---tC interactions are bonding. The He---tC and He---sC bonding interactions are shown to be forced by the high pressure that the helium and carbon atoms exert upon each other in He@adam. The occurrence of a bonding interaction between the helium and sC atoms, which are not linked by a bond path, clearly shows that the lack of a bond path between two atoms does not necessarily indicate the lack of a bonding interaction, as is asserted by QTAIM. IQA calculations showed that not only the destabilization of the adamantane cage, but also a huge internal destabilization of the helium atom, contribute to the metastability of He@adam, these contributions being roughly equal. This result disproves previous opinions based on QTAIM analysis that only the destabilization of the adamantane cage accounts for the endothermicity of He@adam. Also, it was found that there is no homeomorphism of the ρ(r) and -v(r) fields of He@adam. Comparison of the IQA and QTAIM results on the interactions in He@adam exposes other deficiencies of the QTAIM approach. The reasons for the deficiencies in the QTAIM approach are analyzed.

Cyclization of 2-acyl- and 2-thioacylamino- benzylcyclopropanes in the gas phase and solution

Mass spectrometry proved itself to be a powerful tool to predict the directions and yields of mono-molecular reactions of organic compounds. Electron ionization (EI) and electrospray ionization (ESI) were used to study possible transformations of N-(ortho-cyclopropylmethylphenyl)arylamides I and N-(ortho-cyclopropylmethylphenyl)arylthioamides II as well as their para-isomers III and IV in a mass spectrometer and to predict directions and yields of their acid catalyzed cyclization reactions. Several five–eight-membered heterocycles were proposed as possible products of intramolecular transformations of compounds I and II. Reactions of compounds I and II in sulfuric acid solutions were carried out and the results obtained were compared with mass spectrometric data. Surprisingly, EI of the studied compounds mimics their solution reactions better than ESI.

Effect of substituents in the ring on the structure and electron density distribution in benzyl halides

The results of calculations for benzyl chlorides and benzyl bromides that contain substituents in the ring by different quantum-chemical methods are compared. The electron density on the benzyl carbon atom increases as the electron-withdrawing properties of substituents are enhanced due to the shift of the electron density from the benzyl halogen atom to the adjacent carbon atom. A topological analysis according to Bader confirmed the main reason for the change in the paramagnetic shielding of the benzyl13C nuclei. The results of calculations provide, for the first time, an explanation for the resonance upfield13C shift of this atom as the Hammett constant of a substituent increases in compounds of the series under consideration.

The Nature of Metal-Metal Interactions in Dimeric Hydrides and Halides of Group 11 Elements in the Light of High Level Relativistic Calculations

The titular calculations show that charges at metal atoms M are apparently the main factor governing the nature of M⋅⋅⋅M interactions in two-nuclear coinage-metal complexes, and there are certain critical values of positive charges on M atoms, on exceeding which the pair-wise M⋅⋅⋅M interactions and/or the binding between M atoms in such complexes become repulsive despite negative formation energies of such complexes, short M-M internuclear distances, and the existence of a bond critical point (BCP) between M atoms.

Crystal structure of (2PMDETA)-dilithium-1-(cyclononatetraenyl)- enolate, C29H56Li2N6O

C29H56L12N6O, m o n o c l i n i c , P\2\ln\ ( N o . 14 ) , a = 8 . 9 3 6 3 ( 4 ) Ä , b = 2 2 . 9 5 8 ( 2 ) Ä , c = 1 5 . 9 6 1 3 ( 8 ) Ä , β = 9 8 . 7 0 7 ( 5 ) ° , V = 3 2 3 6 . 9 Ä 3 , Z = 4 , R&F) = 0 .038 , wRjeffF1) = 0 .092 , T= 193 K .

STRUCTURES AND HARDNESS OF ETHYL HALIDES AND ETHYL TOSYLATE

Ab initio calculations (RHF) of EtX molecules (X=F, Cl, Br, I, or OTs) were carried out with the use of different basis sets. Total charges on the atoms in the compounds under study were determined by Mullikens, NPA, and Baders methods, and a comparison of these values was performed. For all EtX compounds, a topological analysis of the electron density was carried out within the framework of Baders theory, and the global and relative local hardnesses of the above-mentioned ethylating agents were estimated.

State in solution, structure, and regioselectivity of reactions of the lithium 1-(2-methoxyphenyl)-3,3-diphenylpropyne derivative

According to the spectrophotometric data, the lithium 1-(2-methoxyphenyl)-3,3-diphenylpropyne derivative in diethyl ether exists as contact ion pairs, while in THF, according to the spectrophotometric and13C NMR data, solvent-separated ion pairs are predominantly formed. According to the13C NMR data, the carbanion in the solventseparated ion pairs has a structure close to the propargylic type. The regioselectivity of reactions of the lithium derivative with ethyl halides in diethyl ether, THF, and hexamethyphosphoramide, with benzyl chloride in the first two solvents, and with methanol in THF were studied. The protonation with methanol proceeds exclusively at the allenylic center (C-1) while the ethylation and especially benzylation proceed predominantly at the propargylic center (C-3). The selectivity of ethylation of the propargylic center of both solvent-separated ion pairs in THF and contact ion pairs in diethyl ether increases as the hardness of the ethylating agent increases, and in the case of the same ethyl halide, the selectivity increases from the solvent-separated ion pairs to the contact ion pairs. The spectral data obtained and the data on changes in the regioselectivity do not allow one to believe that the contact ion pairs of the lithium derivative in ether exhibit the intramolecular coordination of the lithium cation to the methoxy group, which might lead to the allenylic structure of contact ion pairs of this derivative.

Effect of the nature of the cation and alkylating agent on the direction of ethylation of 1,3,3-triphenylpropyne salts in ether

Conclusions1.The ratio of the yields of the acetylenic and allenic products decreases in the ethylation of 1,3,3-triphenylpropyne salts in ether with increasing cation size.2.The yield of the acetylenic productdecreases upon the introduction of additives which solvate alkali metal cations and increases in the alkylating reagent series EtI < EtBr < EtCl.