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Neutral zinc(II) O , O ‐di‐alkyldithiopho‐ sphates—variable temperature 31 P NMR and quantum chemical study of the ZDDP monomer–dimer equilibrium
Author(s) -
Harrison J. J.,
Chan C. Y.,
Onopchenko A.,
Pradhan A. R.,
Petersen M.
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2130
Subject(s) - chemistry , dimer , isopropyl , monomer , density functional theory , alkyl , zinc , ring (chemistry) , equilibrium constant , computational chemistry , crystallography , medicinal chemistry , organic chemistry , polymer
A full line‐shape analysis of the VT 31 P NMR spectra was carried out for the monomer–dimer equilibrium of neutral ZDDP. The energy surface and the energetics of the monomer‐dimer equilibrium (Δ H ° , Δ G ° , E a , Δ H ≠ , and Δ G ≠ ) are reported for three variants wherein the alkyl groups in the ZDDP are 2‐ethylhexyl, isopropyl, and isobutyl. We explored a reaction pathway between the monomer and dimer form by means of density functional theory (DFT). The linear combination of atomic orbitals (LCAO) code DMol 3 was used together with a synchronous transient method to effectively locate transition states. Vibrational eigenmodes of all intermediates were computed to capture finite temperature effects. Methyl and ethyl were considered as alkyl groups. Two novel intermediates were located—a four‐membered ring and a six‐membered ring intermediate along the reaction coordinate. Comparison of the experimentally derived and computed energy surfaces was carried out. Copyright © 2007 John Wiley & Sons, Ltd.