%0 Journal Article
%A Orendorff, Christopher J.
%A Ducey,, Michael W.
%A Pemberton, Jeanne E.
%A Sander, Lane C.
%D 2003
%T Structure−Function Relationships in High-Density
Octadecylsilane Stationary Phases by Raman
Spectroscopy. 4. Effects of Neutral and Basic
Aromatic Compounds
%U https://acs.figshare.com/articles/journal_contribution/Structure_Function_Relationships_in_High-Density_Octadecylsilane_Stationary_Phases_by_Raman_Spectroscopy_4_Effects_of_Neutral_and_Basic_Aromatic_Compounds/3582912
%R 10.1021/ac020639g.s001
%2 https://acs.figshare.com/ndownloader/files/5668791
%K material
%K surface coverage
%K Basic Aromatic Compounds
%K compound
%K CH
%K alkyl chains
%X The effects of aromatic compounds (toluene, benzene,
p-xylene, anisole, aniline, and pyridine), temperature, and
surface grafting method (surface- or solution-polymerized)
on alkyl chain rotational and conformational order in a
series of high-density octadecylsilane stationary phases
ranging in surface coverage from 3.09 to 6.45 μmol/m2
are examined by Raman spectroscopy. Rotational and
conformational order are assessed using the intensity ratio
of the antisymmetric to symmetric ν(CH2) modes as well
as the frequency at which the symmetric ν(CH2) band is
observed. Alkyl rotational and conformational order decrease with decreasing surface coverage in these aromatic
compounds, which is consistent with the behavior of these
materials in air and in other solvents. In addition, order
of the alkyl chains is dependent on solvent hydrophobicity,
hydrogen-bonding ability, and basicity. The most hydrophobic compounds impart disorder to the stationary
phase; the hydrogen-bonding aromatics increase the
rotational order of homogeneously distributed, high-surface-coverage materials; and basic aromatic compounds increase the conformational order of high- and
low-coverage materials as the basic compounds undergo
silanophilic interactions with exposed surface silanols.
From these observations, molecular pictures of the chromatographic interface that display interactions between
the alkyl chains and these aromatic compounds are
proposed.
%I ACS Publications