Is Fluorenol polar?
A mixture of fluorene, fluorenone and fluorenol is examined by TLC and gives the following Rf values: 0.3, 0.5, 0.8. -0.8 is fluorene, 0.5 is fluorenone, 0.3 is fluorenol. -Fluorenol is an alcohol, so it is more polar than the ketone fluorenone, giving it a lower Rf value.
It turns out that carbon and hydrogen don't have significantly different electronegativity values. Basically, that means that in our fluorene molecule the electrons (in the form of the covalent bonds) are being shared equally among all atoms. This makes fluorene a non-polar molecule.
- Ethanol is a polar compound, trans-stilbene is nonpolar, 9-fluorenone is moderately polar and benzoic acid is polar compound. So the benzoic acid had the highest R f value.
- Methylene chloride or dichloromethane is moderately polar. Any small molecule cannot be polar or non polar at the same time * polarity is a range. Chlorine being more electronegative than hydrogen causes the dichloromethane molecule to be slightly more negative on the side of the chlorine atoms.
- Toluene is a hydrocarbon (C7H8) and because of the small difference in the electronegativties of C and H, their bond is regarded as nonpolar. Being a hydrocarbon, toluene is a molecule in which all binds are nonpolar and in turn makes it a nonpolar molecule.
Water is very polar and therefore absorbs very strongly on the polar stationary phase (alumina). Since benzil is less polar than benzoin, a polar solvent is used as solvent for the recrystallization. Benzil is less soluble in cold 95 % ethanol than benzoin causing the benzil to precipitate first.
- chemical aspects. Crystallization is a technique that has long been used in the purification of substances. Often, when a solid substance (single compound) is placed in a liquid, it dissolves.
- Explanation: Crystallization is the slow precipitation of crystals from a saturated solution. When it is used to purify an impure solid, the process is often called fractional crystallization or recrystallization. You heat a sample of the impure compound with a suitable solvent, often at its boiling point.
- Crystallisation is a separation technique that is used to separate. a solid that has dissolved in a liquid and made a solution. The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution. A solution that has as much solid dissolved in it.
Column Chromatography is a preparative technique used to purify compounds depending on their polarity or hydrophobicity. In column chromatography, a mixture of molecules is separated based on their differentials partitioning between a mobile phase and a stationary phase.
- Polar compounds will interact with the silica more strongly than non-polar ones so will come off the column, or elute, after non-polar compounds. When a sample contains compounds with similar polarity, the separation between then can be small and recovering all of your clean sample can become a challenge.
- In most column and TLC the stationary phase has a very high polarity and the mobile phase has a lower polarity. Ferrocene is less polar then acetylferrocene. This means that ferrocene will like, or have a higher affinity to the less polar mobile phase than the more polar stationary phase.
- Flash column chromatography is a quick and (usually) easy way to separate complex mixtures of compounds. Column chromatography uses the same principles discussed in the TLC Handout, but can be used on a preparative scale.
Updated: 4th November 2019