Quiz 5 Flashcards
primary alkylated alcohol
C bonded to an OH, 2 Hs, and one R group
secondary alkylated alcohol
C bonded to an OH, 1 H, and two R groups
tertiary alkylated alcohol
C bonded to an OH and three R groups
explain the IUPAC naming for alcohols
*the alcohol should always have the lowest number (it has priority)
*write the substituents in alphabetical order, as well as identifying the position of the -OH group
- select the longest carbon chain and replace the end with -ol
- number the alkyl chain beginning at the end nearest to the hydroxyl group
how would you name a compound with two or three alcohols
diol = 2
triol = 3
describe hydrogen bonding in alcohols and phenols (connect it to BP)
the attraction between the positively polarized OH hydrogen and the negatively polarized oxygen holds the molecules together. When you have a ton of hydrogen bonds (a bunch of OHs connected), these bonds have really high energy which gives them a high boiling point.
phenol pka
9.89
is phenol or alcohol more acidic
phenol because the negative charge in the phenoxide ion is not localized on the oxygen atom, as it is in an alkoxide ion, but is delocalized-it is shared by a number of carbon atoms in the benzene ring. Since it is attached to EWGs, these groups stabilize the ion and lower the pKa of the alcohol.
why is the resonance stabilized phenoxide ion more stable than an alkoxide ion
because the negative charge on the oxygen can be delocalized throughout the ring.
what is an alkoxide ion
An ion with a negative formal charge on oxygen atom bonded to an sp3 carbon atom
what is a phenoxide ion
the conjugate base of phenol (has a -O)
how are alkoxides formed
by reaction with alkali metals (li, Na, or K) OR by deprotonation with a strong base (H-)
how to get an alcohol from an alkene
hydrobromination (1. BH3 2. H2O2, HO-)
how to produce 1, 2 diols from alkenes (CIS OXYGENS)
- OsO4 –> produces an osmate intermediate
- NaHSO3 and H2O
how to produce 1, 2 diols from alkenes (TRANS OXYGENS)
- MCPBA and RCO3H –> produces the intermediate with a triangle and oxygen
- H3O+
what should you do first to convert alcohols into alkyl halides
alcohols must be ‘activated’ (protonated) by a strong acid before they can react
describe reactions of secondary and tertiary alcohols to produce alkyl halides
TWO PATHS: Sn1 and E1rxn
reacts with HBr
- acid protonates most basic atom
- formation of carbocation
3.
For addition: reaction of the carbocation with a nucleophile
For elimination: alkene product undergoes addition rxn
both paths obtain the same product
what kind of intermediates are produced by Sn1 rxns
carbocation intermediates. These will rearrange to produce the more stable product, so watch out.
describe the reaction for primary alcohols to produce alkyl halides
Sn2 rxn
reacts with HBr
- acid protonates the most basic atom
- backside attack by the nucleophile
(but there are better ways to convert primary and secondary alcohols into alkyl halides
best methods to convert primary and secondary alcohols into alkyl halides
- PBr3 —-pyridine—->
- PCl3 —-pyridine—->
- SOCl2 —-pyridine—->
all place alkyl group at the end
explain the significance of sulfonate ester
(ex. tosylate) is a very good leaving group. it is also formed when an alcohol reacts with a sulfonyl chloride
how does the way an alcohol is activated affect the configuration of the alcohol (inversions)
- in two step rxns, 2 inversions occur which gives you the same configuration you started with
- in one step rxns, one inversion occurs which give you the opposite configuration you started with.
is a dehydration rxn reversible
yes
dehydration rxn (fwd) –> remove water
hydration rxn (rev) –> acid within the presence of an excess of water
explain acid-catalyzed dehydration of an alcohol
- elimination rxn (double bond formed)
- needs strong acid catalyst such as H2SO4 or H3PO4 and heat
is dehydration regioselective
yes, the major product is the more stable alkene (the most substituted alkene - Zaitsev’s Rule)
why are tertiary alcohols the easiest to dehydrate
the rate of dehydration reflects the ease of carbocation formation
what should you be careful of for E1 rxns
the formation of a carbocation, because rearrangements can occur.
why don’t we do dehydrations with a primary alcohol
because a primary carbocation is very unstable. Since the E1 mechanism used for secondary and tertiary alcohols relies on a carbocation intermediate, a primary alcohol cannot follow the E1 mechanism
describe dehydration under mild conditions for tertiary, secondary, and primary alcohols
reactants: POCl3 and pyridine –> eliminates
POCl3 is a good dehydrating reagant for primary, secindary, and tertiary alcohols because carbocation rearrangements do not occur.
describe the oxidation of secondary alcohols
OH becomes O double bond using H2CrO4
how to turn a primary alcohol into an aldehyde and then into a carboxylic acid
primary alcohol to aldehyde –> H2CrO4
aldehyde to a carboxylic acid –> further oxidation
how do you have mild oxidation of primary alcohols
(how do you get the oxidation to stop at the aldehyde)
- one must use milder oxidants, such as PCC or Dess-Martin
what are PCC or Dess-Martin used for
oxidize primary alcohols to aldehydes and secondary alcohols to ketones
how do you oxidize a tertiary alcohol
you don’t
