Table 2. Absorption Frequencies of the Carbonyl Group ν(C=O) for Silica-supported Samples of Hexanoic Acid and Corresponding Shift Values Δν(C=O) Relative to ν(C=O) of Monomer and Dimera.
| sample of acid | acid solution in CCl4 (monomer)49 | acid solution in CCl4 (dimer)49 | acid adsorbed on the silica surface from aqueous solution | acid immobilized on the silica surface by impregnation (0.6 mmol·g–1) | ||||
|---|---|---|---|---|---|---|---|---|
| νC=O, cm–1 | νC=O, cm–1 | νC=O, cm–1 | Δν1, cm–1 | Δν2, cm–1 | νC=O, cm–1 | Δν1, cm–1 | Δν2, cm–1 | |
| hexanoic (caproic) 0.503 mmol·g–1 | 1757 | 1711 | 1686 | +25 | +71 | 1685 | +26 | +72 |
| 1703 | +8 | +54 | 1705 | +6 | +52 | |||
| 1716 | –5 | +41 | ||||||
| 1732 | –21 | +25 | ||||||
a
Δν1 = νdimer – νads. – absorption frequencies, νC=O shift of adsorption complex relative to the dimer. Δν2 = νmonomer – νads. – absorption frequencies, νC=O shift of adsorption complex relative to monomer.