Original scientific paper

Acidity Enhancement of the Cyclopentadiene Ring by PH₂ and AsH₂ Substitution

Marcela Hurtado ; Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
Otilia Mó orcid.org/0000-0003-2596-5987 ; Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
Manuel Yáñez orcid.org/0000-0003-0854-585X ; Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain
Jean-Claude Guillemin orcid.org/0000-0002-2929-057X ; Sciences Chimiques de Rennes, Ecole Nationale Supérieure de Chimie de Rennes - CNRS, 35708 Rennes Cedex 7, France

Abstract

The intrinsic acidity of cyclopentadiene and its PH₂ and AsH₂ derivatives has been investigated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d,p) level of theory. The calculated intrinsic acidity of cyclopentadiene is consistent with the available experimental data. Substitution of one of the H atoms of the C(sp3)H₂ group of cyclopentadiene by PH₂ and AsH₂ leads to a significant acidity enhancement of 44 and 34 kJ mol-1, respectively. This acidity enhancement is the result of the balance of two opposite effects: a) a decrease in the aromaticity of the anion on going from the unsubstituted to the substituted
forms, b) the stabilization of the anion in the substituted derivatives, through an interaction of the π-cloud of the ring with the X–H bonding orbitals of the PH₂ or AsH₂ groups. This renders the interaction of the substituent with the five membered ring stronger upon deprotonation, as reflected in a strengthening of the C–P and the C–As bonds.

Keywords

acidity; gas-phase; cyclopentadiene derivatives; density functional theory

Hrčak ID:

37870

URI

https://hrcak.srce.hr/37870

Publication date:

30.6.2009.

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