Variable Temperature FT-IR Studies of n-Alkyl Modified Silica Gels

TLDR: In this article, the conformational state of the alkyl chains in their bound state was monitored via various conformation-sensitive vibrational bands, including symmetric and antisymmetric CH2 stretching bands.

Abstract: Silica gels, chemically modified with n-alkyl chains of various lengths (CnH2n+1, n = 8, 9, 10, 12, 16, 18, 22, and 30), in the dry state were examined over a broad temperature range (123−353 K) via infrared spectroscopy. Here, for the first time a comprehensive variable temperature FT-IR study is available dealing with the conformational order of alkyl modified silica gels. The conformational state of the alkyl chains in their bound state was monitored via various conformation-sensitive vibrational bands. A qualitative statement about the conformational order was possible based on the analysis of the symmetric and antisymmetric CH2 stretching bands. Likewise, CH2 wagging bands were used to identify and determine the relative amountsi.e., integral values over the whole chainsof gauche-trans-gauche, double gauche, and end gauche conformers. The amount of gauche conformers at a specific site in the alkyl chains was accessible via the analysis of CD2 rocking bands of samples bearing selectively deuterated al...