Limonene, Geraniol and Octanal are common fragrance molecules. Octanol-water par

Question

Limonene, Geraniol and Octanal are common fragrance molecules. Octanol-water partition coefficient for these molecules are 4.0, 2.7 and 2.2 respectively. They are dissolved in a micellar solution of SLES and betaine. The partitioning of these molecule into the surfactant micelle will follow the order:

Limonene > Octanal > Geraniol

Geraniol > Octanal > Limonene

Limonene > Geraniol > Octanal

Octanal > Geraniol > Limonene

Limonene > Octanal > Geraniol

Geraniol > Octanal > Limonene

Limonene > Geraniol > Octanal

Octanal > Geraniol > Limonene

Explanation / Answer

Answer: Option C. Limonene > Geraniol > Octanol

Explanation:

Partition coefficient (abbreviated as log P) is a measure of hydrophilicity or hydrophobicity of a compound. It is defined as the ratio of concentrations of solute in between biphasic liquids (where one will be hydrophobic and the other will be hydrophilic)

Significance: The substance with lesser log P values suggest that it is a hydrophilic moeity whereas substance with more log P value infers that the given substance is lipophilic (or hydrophobic)

So, in the given question, Limonene is hydrophobic (lipophilic) and octanal is relatively hydrophilic

Partitioning of Substances in surfactant micelles:

Surfactants are amphiphilic substance which can lower the interfacal tension between two phases. They have a long hydrophobic tail and small polar (hydrophilic head)

So, whenever a high concentration of hydrophobic substance is solubilised into the surfactant micelle, it stabilises the surfactant molecules and do not cause any swelling in the micelle as they are localized in the alkyl chains (tails portion) of the surfactant

On the other hand, hydrophilic subsances travel into the polar group (head) of the surfactant and causes swelling of the micelle which not be stable and lead to disruption of the molecule

So. to conclude lipophilic (or hydrophobic) substance are more rapidly solubilised in surfactants whereas hydrophilic (or lipophobic) substances are relatively less soluble into the surfactant micelle due to the structural disruption

To say this in terms of Octanol- water partition coefficent, substances with low partition coefficient (as they are hydrophilic), they are less soluble in surfactant micelle and substances with more partition coefficient (as they are lipophilic) they are more soluble in the surfactant micelle. In the given example Limonene is more lipophilic, and octanal is more hydrophillic

So, the order of partitioning is:

Option C. Limonene > Geraniol > Octanol (which is similar to their partition coefficient values)

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