TY - JOUR
T1 - Solvent-induced frequency shifts of 5-hydroxymethylfurfural deduced via infrared spectroscopy and ab Initio calculations
AU - Josephson, Tyler R.
AU - Tsilomelekis, George
AU - Bagia, Christina
AU - Nikolakis, Vladimiros
AU - Vlachos, Dionisios G.
AU - Caratzoulas, Stavros
N1 - Publisher Copyright:
© 2014 American Chemical Society.
PY - 2014/12/26
Y1 - 2014/12/26
N2 - Solvent-induced frequency shifts (SIFS) of the carbonyl stretching vibration ν(C=O) of 5-hydroxymethylfurfural were measured in protic, polar aprotic, and nonpolar solvents. The Gutmann acceptor number (AN) was found to correlate with the measured frequency shifts. The SIFS in six solvents were investigated using ab initio electronic structure calculations, treating the solvent implicitly and with an explicit solvent ligand interacting with the carbonyl. The conductor-polarizable continuum model (CPCM) of solvation predicted that ν(C=O) shifted according with the dielectric constant as (ε - 1)/(2ε + 1), in agreement with the analytical predictions of the Kirkwood-Bauer-Magat (KBM) theory for a dipole in a dielectric continuum, but in disagreement with the experimental trend. The experimental SIFS were best predicted using gas-phase complexes of HMF and explicit solvent-ligand. Natural bond orbital (NBO) analysis and Bader's atoms in molecules theory were used to investigate the electronic structure of these complexes. Strong SIFS were found to arise from stronger H-bonding interactions, as observed in delocalization of carbonyl lone-pair electrons by H-bonding solvent σ∗(X-H) orbitals, and an increase in charge density and a decrease in local potential energy at the H-bond (3, - 1) critical point. Consequently, by predicting the experimental SIFS and examining the electronic structure, we find the first theoretical evidence for treating Gutmann's solvent AN as a measure of solvent Lewis acidity. (Graph Presented).
AB - Solvent-induced frequency shifts (SIFS) of the carbonyl stretching vibration ν(C=O) of 5-hydroxymethylfurfural were measured in protic, polar aprotic, and nonpolar solvents. The Gutmann acceptor number (AN) was found to correlate with the measured frequency shifts. The SIFS in six solvents were investigated using ab initio electronic structure calculations, treating the solvent implicitly and with an explicit solvent ligand interacting with the carbonyl. The conductor-polarizable continuum model (CPCM) of solvation predicted that ν(C=O) shifted according with the dielectric constant as (ε - 1)/(2ε + 1), in agreement with the analytical predictions of the Kirkwood-Bauer-Magat (KBM) theory for a dipole in a dielectric continuum, but in disagreement with the experimental trend. The experimental SIFS were best predicted using gas-phase complexes of HMF and explicit solvent-ligand. Natural bond orbital (NBO) analysis and Bader's atoms in molecules theory were used to investigate the electronic structure of these complexes. Strong SIFS were found to arise from stronger H-bonding interactions, as observed in delocalization of carbonyl lone-pair electrons by H-bonding solvent σ∗(X-H) orbitals, and an increase in charge density and a decrease in local potential energy at the H-bond (3, - 1) critical point. Consequently, by predicting the experimental SIFS and examining the electronic structure, we find the first theoretical evidence for treating Gutmann's solvent AN as a measure of solvent Lewis acidity. (Graph Presented).
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U2 - 10.1021/jp508340p
DO - 10.1021/jp508340p
M3 - Article
AN - SCOPUS:84919917993
SN - 1089-5639
VL - 118
SP - 12149
EP - 12160
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 51
ER -