Quiz 2 Flashcards
Acidic Cleavage w/ ether
- using HBr + heat to split an ether into two alkyl halides
- xs HBr needed for two sets of proton transfer and Sn2 mechanism
What happens when a phenyl ether undergoes acidic cleavage
it becomes a phenyl alcohol + akyl halide, not two alkyl halides bc of sp2 hybridization on the ring
Epoxides
cyclic ethers w/ two carbons that have severe ring and torsional strain
What are the two ways you can prepare epoxides?
- MCPBA + Peroxy acid on a double bond
- NaOH on the products of a halohydrin addition reaction
Explain the mechanism of a Halohydrin epoxide preparation
NaOH deprotonates the OH which leads to an intramolecular Sn2 reaction to produce the epoxide
True or false?
Stereochem is preseved in the halohydrin preparation of epoxides but not the MCPBA+ peroxy acid work up
False, stereochem is preserved in both
What are the two ring opening reactions of epoxides?
- reaction with a good nuc
- Acid catalyzed ring opening
Acid catalyzed ring opening
makes the O in the epoxide into a better LG using an acid
What are the mechanistic steps to acid catalyzed ring opening?
- proton transfer
- nucleophilic attack
True or False?
The nucleophilic attack in the second step of acid catalyzed ring opening resembles only a SN2 reaction
False, it has SN2 and SN1 properties
What are the regiochemical rules for nucleophilic ring opening?
attack at the less substitued side
What are the regiochemical rules for acid catalyzed ring opening?
if the epoxide has a tertiary side that side will be attacked but if there is no tertiary side the less substitued side will be attacked
True or False?
You can get the same products from acid catalyzed ring opening that you do from nucleophilic ring opening
False, they have diff regiochemical rules which can give you diff products
Thiols
similar to alchols but with S (-SH), extremely nucleophilic
How do you prepare a thiol?
reacting a NaSH with an alkyl halide
alkyl halide can even be secondary bc SH is very nucleophilic
Mechanism for oxidizing thiols to disulfides
- Thiol +NaOH to deprotonate thiol
- Thiolate + Br2 to attack Br
- Nuc attack by another thiolate to kick off Br and form disulfide
What are the reagents for reducing a disulfide to a thiol?
HCl and Zn
Sulfide
similar to ethers but with S, more reactive than ethers
How can you prepare a sulfide?
the sulfur equivalent of the williamson ether synthesis
still best if alkyl halide is primary
What kind of reactions can sulfides undergo?
1.can act as a nucleophile and attack
2.can be attacked by a stronger nucleophile and act as a LG
Diene
compound with two C=C bonds
What are the three classes of dienes
- Isolated
- conjugated
- Cummulated
Conjugated Diene
bonds are separated by one C/ one sigma bond
How can you prepare a conjugated diene?
Double elimination with dihalide and a strong bulky base to prevent SN2
