Chapter 14

Question 1

Why does an ether have a much lower boiling point than an alcohol?

Answer 1

alcohol - has Hydrogen bonding due to polar O-H bond.

ether - no hydrogen bonding, C-O is polar, but C-H bond is non-polar.

Question 2

Why do ethers with more carbons atoms in their alkyl substituents have higher boiling points?

Answer 2

substituents increase london-dispersion forces between molecules of ether.

Question 3

How do crown ethers create free ions in organic solutions?

Answer 3

the lone pairs on the oxygens interact with cations, freeing anions to be used in reactions, and the non polar outer carbon ring allows crown ethers to dissolve in non polar organic solvents.

Question 4

Why must primary alkyl halide be used in Williamson-ether synthesis?

Answer 4

The second step (attack by the alkoxide ion) is an SN2 reaction.

Question 5

Acidic Cleavage of an ether results in..

Answer 5

two alkyl halides

Question 6

What would be used to convert an ether into two alkyl halides?

Answer 6

acids (like HBr)

and heat

Question 7

Acidic cleavage of phenyl ethers produces what and why?

Answer 7

Phenol and alkyl halide. This reaction stops before making the second alkyl halide due to stability of Phenol (unlikely to be protonated.)

Question 8

Autoxidation

Answer 8

occurs when ether is exposed to atmospheric oxygen and becomes explosive peroxides over time.

Question 9

How can epoxides be synthesized?

Answer 9

peroxyacetic acid epoxidation

OR

cyclicization of halohydrin; form a halohydrin using water and halide (Br2), then treat with a strong base.

Question 10

Why should you use a primary alkyl halide in williamson ether synthesis?

Answer 10

because this reaction is an SN2 type mechanism, and primary halides react faster, giving a higher product yield.

Question 11

What is the best way to form cyclic ethers?

Answer 11

cyclization of halohydrins.

Question 12

Why are epoxides able to undergo base-catalyzed ring opening, while ethers cannot?

Answer 12

epoxides have high ring strain, which lowers the activation energy, which compensates for the poor leaving group (alkoxide ion.)

Question 13

Under basic conditions, with an alkoxide present, an ethoxy group will form at which carbon and why?

Answer 13

the less-substituted/hindered carbon - SN2 reaction.

Question 14

Under acidic conditions, with an alcohol present, an ethoxy group will form at which carbon and why?

Answer 14

the more substituted carbon, b/c this carbon is a more stable/stronger (partial) carbocation for a weak nucleophile like ethanol to attack.

Question 15

What is the expected product in a reaction of an epoxide with a grignard reagent?

Answer 15

ring-opened alcohol

Question 16

How are sulfides generated?

Answer 16

Williamson ether synthesis using thiolate ion as the nucleophile.

Question 17

Are thiolate ions or alkoxide ions better nucleophiles, and why?

Answer 17

Thiolate ions - b/c sulfur is larger and more polarizable than oxygen.

Question 18

When an epoxide reacts with an organometallic reagent, which carbon (of an unsymmetrical epoxide) gains the alkyl group?

Answer 18

the less substituted carbon - b/c it allows for unhindered nucleophilic attack, though grignard’s may give both products.