Arturo Arnau

ROTATIONAL CONSTANTS AND DIPOLE MOMENTS OF INTERSTELLAR POLYYNES : A COMPARATIVE MP2 AND DENSITY FUNCTIONAL (BP86) STUDY

Abstract By means of theoretical calculations the rotational constants and dipole moments of the first members of the polyynes families (cyanopolyynes, methylcyanopolyynes and isocyanopolyynes) have been calculated at the MP 2 6-31 G ∗ and BP 86 6-31 G ∗ levels. The calculations of rotational constants given in this paper show that the predicted values using density functional theory are in reasonable agreement with the experimental and the MP2 results. A good evaluation of the dipole moments requires the introduction of the electronic correlation, which can be made using density functional calculations. The results are considerably improved using a least squares fit between the experimental and calculated dipole moments including electronic correlation.

Theoretical rotational constants of MeCnN species

Abstract By means of SCF HF “ab initio” calculations with STO-3G and 6-31G basis sets, the geometric parameters of methylcyanopolyynes (MeCnN n=3, 5, 7 and 9) have been obtained. B0=0.3748 GHz for MeC7N and B0=0.2708 GHz for MeC9N, with a STO-3G basis set, were obtained. Both species, unstable in the laboratory, are still undetected in the interstellar medium, although their existence is very probable.

Relative strength of BF3 and BCl3 as Lewis acids

The acidity order: BF3 < BCl3 found by ab initio calculations agrees with experimental data. The reasons for the weaker acceptor properties of BF3 in comparison with BCl3 are discussed.

A theoretical study of the intramolecular solvolytic mechanism of the Meyer–Schuster reaction. MINDO/3 and CNDO/2 calculations of minimum energy paths

Abstract Theoretical results give strong support to an intramolecular solvolytic mechanism for the Meyer–Schuster rearrangement. Both CNDO/2 and MINDO/3 reaction paths suggest that the possibility of a 1,3 propargylic shift across the triple bond in a model α-acetylenic tertiary alcohol can be discarded. The electronic structure of the reaction intermediate corresponds to an alkynyl cation interacting electrostatically with a water molecule. For non-aqueous solvents this result agrees with the formation of a stable alkynyl carbocation, which has been found experimentally. For aqueous solvents the nature of the reaction path leads to the conclusion that the intermolecular mechanism which has been proposed for this reaction is more realistic.

Ab initio rotational constants of isocyanopolyynes

The ab initio rotational constants of the isocyanopolyynes of formulae HC 5 N, HC 7 N, HC 9 N, and HC 11 N have been calculated. Their respective values are 1.3925, 0.5653, 0.3111, and 0.1869 GHz, respectively. Inaccuracies of just a few tenths of 1% may be expected. The recent discovery of isocyanopolyynes, and the presence of cyanopolyynes in different interstellar clouds allow one to think that the isocyanopolyynes studied here may be detected in the near future

Electronic structure of Friedel-Crafts catalysts, an ab initio study of the RF-BF3 adducts

By means of ab initio calculations using several basis sets (STO-3G, 3-21G, and 6-31 +G), the minimum-energy structures for the RF–BF3 intermediates (R = H, Me, and Et) of the Friedel–Crafts alkylation reaction have been obtained. The role of the catalyst in the process through an analysis of dissociation energies, atomic charges, and LUMO energies of reaction intermediates, and the same quantities for the RF species, has been studied.

Calculated rotational constants of interstellar species - Hydrogenated derivatives of HCN and HC3N

By means of ab initio calculations with different basis sets, from a minimum STO-3G basis set up to a 6-31 G* basis set, both with and without inclusion of electron correlation, the energies, geometries, rotational constants, and dipole moments of the 18 hydrogenated derivatives of hydrogen cyanide (HCN) and cyanoacetylene (HC 3 N) have been calculated. The theoretical predictions should prove useful for laboratory and astronomical studies of these species. Some of these molecules have already been discovered in the interstellar medium while others are as yet undetected there, although their presence is probable. The rotational constants herein provided could help in the detection of these in the interstellar medium