ORGANIC CHEMISTRY I CHEM 2323

CHAPTER 6 - ALCOHOLS AND ETHERS

STRUCTURE OF ALCOHOLS

ROH

CLASSIFICATION OF ALCOHOLS

NOMENCLATURE OF COMMON NAMES

Name the alkyl group then add the word "alcohol" to the end

IUPAC NOMENCLATURE

• Longest chain containing -OH
• Replace "e" in parent name with "ol"
• "-OH" gets priority for numbering parent chain.

PHYSICAL PROPERTIES

The -OH part is polar, the R part is nonpolar.

As the alkyl (R) gets larger, the molecule gets less polar.

As the molecular weight increases, the boiling point (BP) increases.

As branching increases, the boiling point decreases.

INDUSTRIAL SOURCES OF ALCOHOLS

1. Hydration of alkenes

2. Oxo Process

3. Fermentation of Carbohydrates

PREPARATION OF ALCOHOLS

1. Hydrolysis of alkyl halides

2. Synthesis Grignard

REACTIONS OF ALCOHOLS

The chemical properties of an alcohol are determined by its functional group -OH.

Reactions of an alcohol can involve the removal of the entire -OH or just the H.

Either kind of reaction can involve substitution, in which a group replaces the -OH or -H, or elimination, in which a double bond is formed.

1. Reaction with hydrogen halides

 

reactivity of HX: HI > HBr > HCl

reactivity of ROH: alkyl, benzyl > 3^o > 2^o > 1^o

The reaction is mostly S_N1 which forms a carbocation so rearrangement can occur.

2. Reaction with phosphorus trihalides

3. Dehydration

4. Reaction as acids: reaction with active metals

5. Ester Formation

6. Oxidation

primary alcohol

secondary alcohol

tertiary alcohol

 

ETHER STRUCTURE

R - O - R

Ethers Video Lecture

COMMON NAMES OF ETHERS

Name the two R's and add "ether" to end.

IUPAC NAMES OF ETHER

Use the longest chain of carbons for the parent name and list the -OR portion as a side group. The ether side group gets no priority.

PHYSICAL PROPERTIES

Boiling point (BP) of ethers is approximately the same as alkanes with similar molecular weights.

Boiling point of ethers are lower than similar alcohols.

Solubility in water is about the same as alcohols.

INDUSTRIAL SOURCES OF ETHERS

A number of symmetrical ethers (where the Rs are idential on both sides) are used for solvents.

HAZARDS OF ETHERS

Upon standing in contact with air, most aliphatic ethers are slowly converted into unstable peroxides. These peroxides can cause explosions. The smaller ethers are very volatile with low boiling and flash points (flammable). The presence of peroxides can be indicated by the formation of a blood red colour in the following reaction.

Peroxides can be removed by washing with solutions of ferrous ions or distillation from concentrated H₂SO₄.

Williamson Synthesis

Williamson Synthesis can be used to make both symmetrical and unsymmetrical ethers.

REACTIONS OF ETHERS

ANALYSIS OF ALCOHOLS

• dissolve in cold H₂SO₄
• do not decolorize in Br₂ in Ccl4
• CrO₃ in aqueous H₂SO₄ within 2 seconds turns the orange solution to blue-green and becomes opaque.