Hydroxy Functional Group - Alcohols | Organic Chemistry 1
Properties of Alcohols
Because of the electronegativity of the oxygen, alcohols exhibit molecular polarity
⇒ Alcohols are soluble in water and polar solvents
The hydroxy hydrogen enters into hydrogen bonding with other alcohol molecules
⇒ High boiling point compared to the corresponding alkanes
Alcohols are amphoteric
⇒ they can be deprotonated by strong bases or protonated by strong acids
Naming the Alcohols
- Find the longest chain containing the OH.
- Number the chain starting at the end nearer the OH.
(If equal, begin at the end nearer the first branch point).
- Place the number of the position of OH before the parent name.
Use the suffixes diol, triol ... if more than one OH.
The names of the substituents are added as prefixes.
- For cyclic alcohols, the carbon bearing the OH receives the number 1
(it does not need to be mentioned if there is only one substituent).
Synthesis of Alcohols by SN Reactions
To prevent the competition between SN and E reactions ⇒ replace the halogen atom by a good leaving group:
Synthesis of Alcohols by Reduction of Carbonyls
Carbonyl groups: C=O bond.
⇒ formed by oxidation of alcohols using Na2Cr2O7 or PCC
Alcohols can be synthesized by reduction of carbonyls using H- donors (NaBH4 or LiAlH4).
H- reacts with an electrophile and so with the C of the carbonyl.
Oxydation and Reduction of alcohols:
Synthesis of Alcohols with Organometallics
Alcohols can be synthesized by using organometallics, R- donors.
3 types of organometallics (R = alkyl chain):
- Alkyl lithium: RLi (R-Li+)
- Grignard reagent: RMgBr (R-BrMg+)
- Gilman reagent: R2CuLi (R-RCu+Li)
Synthesis of Organometallics:
R- (like H-) reacts with an electrophile and so with the C of the carbonyl:
Reactions of Organometallics R-M (M= Li, MgBr or RCuLi):
- synthesis of alcohol + C-C bond formation
- C-C coupling reactions (only with Gilman reagent)
- strong reaction with water