Quiz 1 Flashcards
-OH group=
alcohol
Ph-OH =
Phenol ring+ OH
hydroxyl group
Bc of ——- alcohols have higher bp
hydrogen bonding
Alkoxide
conjugate base of an alcohol w/ a negative O
Alcohols are more acidic than amines +alkanes but less acidic than ——-
hydrogen halides
What kind of bases are needed to deprotonate an alcohol?
N-,C-,H-
strong bases, unless its a hydroxyl group
What are the three stabilizing effects for alkoxides
- resonance
- induction
- solvation/steric hinderence
True or False?
A weaker, well stabilized base will have more steric hinderence to protect it from solvent effects
False, less steric hinderence allows the solvent to stabilize a charge creating a weaker base and stronger acid
If you want to prepare an alcohol via substitution what kind of substrate must it be?
Primary or tertiary
secondary = elimination
What are the three addition reactions that can be used to prepare alcohols?
- Acid cataylized hydration
- Oxymercuration demurcuration
- Hydroboration oxidation
Oxidation
increases the number of electrons, increases the number of bonds between C and an electronegative atom
Reduction
decreases the number of electrons, decreases the number of bonds between C and an electronegative atom
name the three reduction agents for reducing ketones/aldehydes to alcohols
- Hydrogenation of an alkene with a metal catalyst
- NaBH4 (mild reagent)
- LiAlH4 (strong reagent)
Why isnt hydrogenation of alkene used often for reduction of alcohols?
Bc it requires harsh conditions
What are the mechanistic steps for using NaBH4 as a reducing agent?
- nuc attack by hydride source
- proton transfer from solvent to O- for neutralization
What are the mechanistic steps for using LiAlH4 as a reducing agent?
- add LiAlH4 as a hydride source for nuc attack
- add solvent separately to LiAlH4 for neutralization/ proton transfer step
LiAlH4 and NaBH4 react — with C=O bonds
selectivley
Mechanistic steps for reduction of an ester using LiAlH4
- need 2 eq. of hydride
1. nuc attack by hydride source
2. loss of leaving group by other O group to reform C=O bond
3. nuc attack by hydride source
4. proton transfer/ neutralization
Grignard reagent
R-Mg-X
- prepared by reaction of Mg + alkyl halide
What is special about the C-Mg bond in the grignard reagent?
it can be deemed an ionic bond where the C has a partial negative charge, giving it nucleophilic qualities
Why would you have to protect an alcohol?
Bc if it is used with a grignard reagent the reagent would react with itself and not the C=O bond
What is an example of a protecting group?
TMSCl
What are the three steps for protection of alcohols?
- replace proton on unwated alcohol with protecting group
- Proceed with reaction of the grignard agent+ substrate
- deprotecting alcohol and regenerate proton
examples of deprotecting agents
- TBAF/F-
- H3O+
What kind of reactions can a tertiary alcohol undergo?
SN1 reaction w/ HX as the reagent
What kind of reactions can a secondary alcohol undergo?
- SN2 by converting OH` to OTMS and using a strong nuc only
- SN2 by using PBr3 or SOCl2
- elimination by strong base
What kind of reactions can a primary alcohol undergo?
- SN2 by treatment w/ HBr
- SN2 by conversion of OH to OTMS and using a good nuc only
- SN2 by SOCl2 and PBr3
What is the one step featured in all of the substiutuon reactions with alcohols?
Turning the OH group into a better leaving group
explain an E1 reaction w/ an alcohol
- youll need acidic conditions + heat
- tertiary alcohol to prevent re-arrangements
explain and E2 reaction w/ an alcohol
- a strong base must be used (ex: TBuOK)
- E2 does not have rearrangements
What are two oxidixing reagents for oxidation of an alcohol?
PCC and Chromic acid
PCC = mild Chromic= strong
If a primary alcohol is oxidzized with chromic acid what is the product?
carboxylic acid
How many oxidations can a secondary alcohol go through?
only one bc it has one hydrogen
What is the product of a tertiary alcohol reacted with chromic acid?
none, tertiary alcohols cannot be oxidized, they have no hydrogens
IUPAC naming of Ethers
choosing the longest R group of the ether to be the parent chain and naming the shorter one as an oxy substituent
recall that ethers are low on the priority list
Why do ethers not have a high bp?
bc they have no hydrogen bonding like alcohols
Why are ethers often used as organic solvents?
Bc/ they are not very reactive and have low bp
Williamson Ether synthesis
- Sn2 like process
- Proton transfer to create alkoxide intermediate and then nuc attack where alkoxide acts as the nucleophile
- Alkoxide key intermediate
- can only be done with primary or secondary alkyl halides
Alkoxymercuration demercuration
- very similar to the alkene rxn of the same name
- ROH group added via markovnikov addition instead of OH
