Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Ethers are organic compounds with the general formula , where and can be alkyl or aryl groups.
Preparation by Dehydration of Alcohols: Primary alcohols undergo dehydration in the presence of protic acids (, ) at to form ethers. At higher temperatures (), alkenes are the major product.
Williamson Synthesis: This is an reaction between an alkyl halide and a sodium alkoxide (). It is most successful with primary alkyl halides. If a tertiary alkyl halide is used, elimination occurs to form an alkene.
Physical Properties: Ethers have lower boiling points than isomeric alcohols because they cannot form intermolecular hydrogen bonds. However, they are soluble in water to an extent similar to alcohols of comparable molecular mass due to hydrogen bonding with molecules.
Cleavage of C-O bond by Hydrogen Halides (): Ethers react with concentrated or to form an alcohol and an alkyl halide. The reaction follows mechanism for primary/secondary groups (halide attacks the smaller alkyl group) and if one of the alkyl groups is tertiary.
Electrophilic Substitution in Aromatic Ethers: The alkoxy group () is ortho-para directing and activates the aromatic ring towards electrophilic substitution (Halogenation, Nitration, Friedel-Crafts reaction).
📐Formulae
💡Examples
Problem 1:
Predict the products of the reaction between and .
Solution:
Explanation:
The reaction follows an mechanism. The nucleophile attacks the less sterically hindered carbon atom of the smaller alkyl group (), resulting in methyl iodide and ethanol.
Problem 2:
What happens when reacts with ?
Solution:
Explanation:
This is a Williamson synthesis. Since the alkyl halide is primary (), the reaction proceeds smoothly to form ethyl tert-butyl ether. Elimination is not the major pathway here because the halide is not tertiary.
Problem 3:
Write the major product for the Nitration of Anisole ().
Solution:
4-Nitroanisole (p-nitroanisole)
Explanation:
The methoxy group () is an activating and ortho-para directing group. Due to steric hindrance at the ortho position, the para-isomer is the major product when reacted with a mixture of conc. and conc. .