Premium
Formation mechanism of acetaldehyde lithium enolate by reaction of n ‐butyllithium with tetrahydrofuran: infrared and Raman spectroscopy and density functional theory calculations
Author(s) -
Corset Jacques,
CastellàVentura Martine,
Froment Françoise,
Strzalko Tekla,
Wartski Lya
Publication year - 2002
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.896
Subject(s) - chemistry , tetrahydrofuran , dimer , density functional theory , butyllithium , raman spectroscopy , infrared spectroscopy , molecule , lithium (medication) , computational chemistry , photochemistry , solvent , medicinal chemistry , organic chemistry , medicine , physics , optics , endocrinology
Depending on the reaction conditions, n ‐butyllithium ( n ‐BuLi), as a base, may react both with the reactants and with the solvent. Thus, it has been shown that the n ‐BuLi dimer reacts with tetrahydrofuran (THF) to give acetaldehyde lithium enolate (CH 2 CHOLi). The density functional theory approach at the B3‐LYP level with the 6–31 + G* basis set is applied to determine the geometrical, energetic and vibrational characteristics of the different aggregates of the acetaldehyde lithium enolate involved in the cleavage of THF by n ‐BuLi. Calculations show that two types of anions may be distinguished in these aggregates, the O and π(CC)—Li bound one (pyramidal structure) and the only O—Li bound one (linear structure). In parallel, infrared (IR) and Fourier transform Raman spectroscopy allow one to determine the vibrational properties of the different enolate aggregates and to specify the mechanism of the THF cleavage. First, the n ‐BuLi dimer reacts with a solvating THF molecule, leading to a reaction intermediate, the mixed aggregate (CH 2 CHOLi, n ‐BuLi). Then, this aggregate reacts with a second solvating THF molecule, giving rise to the trans linear–linear enolate dimer, which further dimerizes to form a tetramer. The very good agreement between theory and experiment concerning the wavenumbers and the IR intensities allows one to validate the calculated structures of the different enolate aggregates. Copyright © 2002 John Wiley & Sons, Ltd.