Chapter 12 - Alcohols Flashcards
What is an alcohol?
Alcohols possess a hydroxyl group (-OH)
What is a phenol?
Phenols possess a hydroxyl group directly attached to an aromatic ring
Alcohol and phenol classification: Nomenclature procedure (5 steps)
- Identify the parent chain, include -OH even if it makes the chain shorter
- Identify, name, and alphabetize substituents
- Assign locants and prefixes to each substituent, give the lowest locant to the -OH
- Place -OH locant just before -ol suffix in parent chain
- Address stereochemistry
* Cyclic alcohols: -OH is assumed to be on carbon 1, locant is assumed
Common alcohol names (3)
Iso-propyl alcohol, turt-butyl alcohol, benzyl alcohol
Properties of alcohols (4)
- Raises boiling point (intermolecular forces)
- Miscible in water if less than eight carbons
- More acidic than amines and alkanes (resonance, induction, solvation)
- Deprotonated by NaH or Na with K/Li
Preparation of alcohols: SN2
(Starting materials, reaction conditions, major products)
Starting material: Primary alkyl halide
Reaction conditions: NaOH
Products: Primary alcohol
Preparation of alcohols: SN1
(Starting materials, reaction conditions, major products)
Starting material: Tertiary alkyl halide
Reaction conditions: H2O
Products: Tertiary alcohol
Preparation of alcohols: Addition (3 types)
(Starting materials, reaction conditions, major products)
- Starting material: Alkene
Reaction conditions: Dilute H2SO4
Products: Secondary alcohol
*Rearrangements - Starting material: Alkene
Reaction conditions: 1) Hg(OAc), H2O | 2) NaBH4
Products: Secondary alcohol - Starting material: Alkene
Reaction conditions: 1) BH3-THF | 2) H2O2, NaOH
Products: Primary alcohol
Preparation of alcohols: Reduction (3 types)
(Starting materials, reaction conditions, major products)
- Starting material: Carbonyls, alkenes, alkynes
Reaction conditions: H2, Pt or Pd or Ni
Products: Secondary alcohol
Will reduce all alkenes and alkynes - Starting material: Ketones, aldehydes, imines
Reaction conditions: NaBH4, EtOH or MeOH or H2O
Products: Secondary alcohol
Will only reduce carbonyl - Starting material: Ketones, aldehydes, imines, esters, carboxylic acids
Reaction conditions: 1) LAH | 2) H2O
Products: primary alcohol
Draw a mechanism for alcohol formation via reduction with BH4
Seriously, draw it.
Draw a mechanism for alcohol formation via reduction with LAH
No skipping!
Calculating carbon oxidation number (2 steps)
- Give electrons heterolytically to more electronegative atom
- Oxidation # = Valence - # of electrons on the carbon
What does an increase in an atom’s oxidation number mean? What about a decrease?
Increase in an atom’s oxidation number means the atom has been oxidized. A decrease means the atom has been reduced.
Why won’t tertiary alcohols undergo oxidation?
There are no hydrogens to remove
How do you name a diol? IUPAC? Common name?
Name using “diol” suffix and give a locant for each hydroxyl for IUPAC
Common names use “glycol”
How do you prepare a diol?
Reduce a di-carbonyl or syn/anti dihydroxylate an alkene
Draw a generic Grignard reagent
R-Mg-X
Why must water be avoided in the presence of a Grignard reagent?
The Mg-C bond has high ionic character that makes the carbon act as a nucleophile and/or a base. As a base, it will react with the water instead of completing the desired reaction.
How does a Grignard reagent react in the presence of a carbonyl? What about an ester?
The Grignard reagent will form an -OH (reduce the carbonyl) and form a new C-C bond (adds on whatever alkyl group is attached to the reagent).
The reagent will react twice with an ester and add two R groups
Draw the mechanism for a Grignard reaction
Dude, you know whichever mechanism you don’t practice will be on the test.
What are the starting materials for a Grignard reaction? Reaction conditions? Product?
Grignard reagents react with carbonyls to produce alcohols.
Reaction conditions: 1) RMgBr | 2) H2O
What is the name of the synthesis strategy used to overcome reaction incompatibilities?
Protection/deprotection strategy
Explain the general steps (3) of a protection/deprotection strategy and name reagents involved in each step
Protect the carbonyl/oxygen by using TMS-Cl, Et3N. Perform the Grignard reaction using 1) RMGBr | 2) H2O.
Deprotect by using TBAF
Will Grignard reactions work on -OH groups?
No, the -OH will quench the reagent
Reaction conditions for the halogenation of alcohols: SN1
H-Br
[G]
* Tertiary alcohols
Reaction conditions for the halogenation of alcohols: SN2
H-Br
[G]
* Primary alcohols
Reaction conditions (2) for the halogenation of alcohols: Chlorination
HCl, ZnCl2
[CCC]
* Primary alcohols
SOCl2, Pyridine
[L]
* Primary/secondary alcohols
Reaction conditions for the halogenation of alcohols: Bromination
PBr3
[BBB]
* Primary/secondary alcohols
Reaction conditions for the halogenation of alcohols: Any halogen
TsCl, Pyridine
[C]
* Primary/secondary alcohols
Reaction conditions for the elimination of alcohols: E1
H2SO4, heat
[F]
* Tertiary alcohols
Reaction conditions for the elimination of alcohols: E2
TsCl, Pyridine, NaOEt
[C]
* Tertiary alcohols
Reaction conditions (2) for the oxidation of alcohols: Primary alcohols
Na2Cr2O7, H2SO4, H2O
[I]
* Will oxidize all the way to a carboxylic acid
PCC, CH2Cl2
[VV]
* Will stop at an aldehyde
Reaction conditions for the oxidation of alcohols: Secondary alcohols
PCC, CH2Cl2
[VV]
Reaction conditions for the oxidation of alcohols: Tertiary alcohols
Sorry, this one’s a trick. Tertiary alcohols can’t be reduced - they don’t have any hydrogens.
Draw a general oxidation of a secondary alcohol using chromic acid.
Keep practicing :)
What reaction conditions will cause the oxidation of an alcohol to a carbonyl?
PCC, DCM
[VV]
Name a biological redox reagent
NAD+/NADH
Phenols oxidize to form ___________
Benzoquinones
