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CHEM 219 UNIT 5 EXAM 2025 QUESTIONS
AND ANSWERS .
Nomenclature for crown ethers - correct answer - The naming conventions for crown ethers follow the pattern "[x]crown-y", where "x" is a number that reflects the ring size, and "y" represents the number of oxygen atoms. The oxygen atoms are usually separated from one another by two carbon atoms.
What is the special ability of crown ethers? - correct answer - Crown ethers are a special class of ethers, as they have the ability to solvate cations (+) within the interior cavity of their ring structures. The lone pairs of the oxygen atoms in the ring can bind to cationic species and hold them. The size of the ring controls which cations can fit into the cavity.This phenomenon is important because it allows ionic compounds to be dissolved in relatively non-polar organic solvents.
Why do ethers have lower boiling points than that of an alcohol of the same molecular weight? - correct answer - Due to their atomic connectivity, ethers do not have any O-H covalent bonds and, thus, are incapable of forming hydrogen bonds with one another.The lack of intermolecular attraction causes ethers to boil at much lower temperatures than their constitutionally isomeric alcohols. 1 / 3
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The boiling point of an ether is very similar to a hydrocarbon of corresponding molecular weight
What type of hydrogen bonds can ethers do? - correct answer - Although ethers cannot form hydrogen bonding attractions with molecules of each other, the lone pairs of electrons on the oxygen of an ether can form hydrogen bonds to molecules that have O-H, N-H, or S-H bonds as a part of their structure. In other words, ethers cannot donate hydrogen bonds but can accept them from other molecules. Ethers can accept hydrogen bonds from alcohols, and water.
What happens to the water solubility of an ether as the size of the R groups of an ether increases? - correct answer - As the size of the R groups of an ether increases, the water solubility of the ether decreases as the hydrocarbon portion of the molecule overwhelms the ability of the molecule to make hydrogen bonds.
Describe ethers as solvents - correct answer - Ethers are relatively inert compounds. For this reason, they are often used as solvents for reactions or to prepare solutions containing relatively reactive materials. Most organic compounds dissolve in ethers.
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Ethers as extraction solvents - correct answer - Used to isolate/collect organic compounds from their natural sources. The low boiling point of ethers makes them easy to remove from an extract.
Volatility of ethers - correct answer - Ethers, in general, are volatile (low boiling point). This volatility presents a danger as well
- most small ethers are highly flammable and should not be used
in a location where sources of open flame are found (such as Bunsen or Fisher burners). Electrically operated heat sources or steam are used to heat ether-based (ethereal) solutions. Long- term exposure to oxygen in air can cause the formation of explosive peroxides in ethers.
Why is the dehydration of alcohols to produce ethers limited to the synthesis of symmetric ethers from primary alcohols? - correct answer - If the desired ether is asymmetric, or the complexity of the R groups increases, the overall yield of the desired ether product is reduced.
With the goal of forming more complex ethers (especially asymmetric ethers), what is one mode of preparation available but not the most preferred option? - correct answer - addition of alcohols to alkenes
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