Here are the essential concepts you must grasp in order to answer the question correctly.
Polarity
Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between their atoms, tend to interact well with water, a polar solvent. In contrast, nonpolar molecules do not dissolve well in water due to their lack of charge separation.
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Hydrogen Bonding
Hydrogen bonding is a type of strong intermolecular attraction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen or nitrogen. In the context of solubility, compounds that can form hydrogen bonds with water, such as alcohols, are generally more soluble than those that cannot, as these interactions help to stabilize the solute in the solvent.
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Functional Groups
Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the case of the compounds in the question, the presence of the hydroxyl (-OH) group in 1-butanol enhances its solubility in water compared to methyl propyl ether, which lacks this polar functional group.
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