In: Chemistry
A C-O bond is technically more polar than a C-N bond, but nitrogen containing compounds frequently have lower Rf values than their oxygen containing counterparts. Explain this phenomenon.
Does the polarity of the solvent affect the Rf value of a compound? Should it change the order of the compounds on a TLC plate?
C-O and C-N bond polarity is defined based on the electronegativity difference between C,O and C,N. But when it comes to chromatography, we need to consider the mobile phase and stationary phase too.
In TLC, generally silica gel is used as stationary phase. Silica is slightly acidic in nature due to the presence of OH groups on the surface of the silica gel. any basic compound run through the silica gel interacts strongly with the surface of the slica gel due to this reason. This is the same reason why amine which is basic in nature, with a free lone pair on the nitrogen atom, eludes slowly when compared compounds containing oxygen atom.
Surely, the polarity of the solvent affects the Rf value of the compound. Polarity of the solvent determines the solubility of the compound in it. If the compound non-polar, then non-polar solvents move the non-polar compounds faster when compared to polar compounds. Generally, as the polarity of solvent increases, the Rf value of compound increases.