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Acidity Trends in α,β‐Unsaturated Sulfur, Selenium, and Tellurium Derivatives: Comparison with C‐, Si‐, Ge‐, Sn‐, N‐, P‐, As‐, and Sb‐Containing Analogues
Author(s) -
Guillemin JeanClaude,
Riague El Hassan,
Gal JeanFrançois,
Maria PierreCharles,
Mó Otilia,
Yáñez Manuel
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400989
Subject(s) - selenium , tellurium , sulfur , chemistry , chalcogen , inorganic chemistry , organic chemistry
The gas‐phase acidity of CH 3 CH 2 XH (X=S, Se, Te), CH 2 CHXH (X=S, Se, Te) and PhXH (X=S, Se) compounds was measured by means of Fourier transform ion cyclotron resonance mass spectrometry. To analyze the role that unsaturation plays on the intrinsic acidity of these systems, a parallel theoretical study, in the framework of the G2 and the G2(MP2) theories, was carried out for all ethyl, ethenyl (vinyl), ethynyl, and phenyl O‐, S‐, Se‐, and Te‐containing derivatives. Unsaturated compounds are stronger acids than their saturated analogues, because of the strong π‐electron donor ability of the heteroatoms that contributes to a large stabilization of the unsaturated anions. Ethynyl derivatives are stronger acids than vinyl compounds, while phenyl derivatives have an intrinsic acidity intermediate between that of the corresponding vinyl and ethynyl analogues. The CH 2 CHXH vinyl compounds (enol‐like) behave systematically as slightly stronger acids than their CH 3 C(H)X (keto‐like) tautomers. Vinyl derivatives are stronger acids than ethyl compounds, because the anion stabilization attributable to unsaturation is greater than that undergone in the neutral compounds. Conversely, the enhanced acidity of the ethynyl derivatives with respect to the vinyl compounds is due to two concomitant effects, the stabilization of the anion and the destabilization of the neutral compound. The acidities of ethyl, vinyl, and ethynyl derivatives containing heteroatoms of Groups 14, 15, and 16 of the periodic table are closely related, and reflect the differences in electronegativity of the CH 3 CH 2 , CH 2 CH, and CHC groups.