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chem 219 module 5 Test with Questions Solved 100% Correct | Latest Update
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chem 219 module 5 Test with Questions Solved100% Correct | Latest Update
Epoxides - ✔✔Three-membered cyclic ethers, composed of two carbon atoms
Epoxides are also known as oxiranes. The small, three-membered ring of an
epoxide is very highly strained (severe angle strain), and as a result, epoxides are
useful in synthesis where atoms or groups can be added to the epoxide molecule
using a ring-opening reaction.
crown ethers - ✔✔Macrocyclic (large ring) polymeric ethers are known as
crown ethers because their rings have a distinct repeating pattern that resembles
a crown.
Nomenclature for crown ethers - ✔✔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? - ✔✔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? - ✔✔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.
The boiling point of an ether is very similar to a hydrocarbon of corresponding
molecular weight
What type of hydrogen bonds can ethers do? - ✔✔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? - ✔✔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 - ✔✔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.
Ethers as extraction solvents - ✔✔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 - ✔✔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? - ✔✔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? -
✔✔addition of alcohols to alkenes
During this reaction an alcohol is used as the solvent instead of water and acts as
the nucleophile, resulting in the overall addition of H (from the acid catalyst) and -
OR (from the alcohol) across the double bond of the alkene, breaking the double
bond and forming a more complex/asymmetrical ether.
With the goal of forming asymmetric ethers, what mode of preparation
preferred? What are the steps? - ✔✔Williamson Synthesis
This method uses two steps to produce an asymmetric ether.
1. In the first step, an alcohol is converted to its conjugate base (alkoxide ion, RO-)
usually by reacting the alcohol with sodium or potassium metal.
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