Amides - Functional Group

What are Amides?

Amides are organic compounds characterised by a carbonyl group (C=O) connected to a nitrogen atom (N).

Differentiation

• Amines vs Amides:
  • Amines: Do not contain a carbonyl group.
  • Amides: Include a carbonyl group.
• Esters vs Amides:
  • Esters: Contain an oxygen atom bonded to the carbonyl group.
  • Amides: Feature a nitrogen atom bonded to the carbonyl group.

Structural Formula

The general structural representation of amides is R-CO-NR'R''.

• Example Table:

  Compound	Structural Formula
  Acetamide	CH₃CONH₂
  Formamide	HCONH₂

Nomenclature Basics

Naming Conventions

• Derived from carboxylic acids and alkyl groups.
• Example: Acetic Acid gives rise to Acetamide.
• Substituted Amides:
  • Example: N-methylacetamide denotes a methyl group attached to nitrogen.

Example Table:

Base Acid	Amide Name
Acetic Acid	Acetamide
Formic Acid	Formamide

Role in Peptide Bonds

• Peptide bonds incorporate amide linkages, essential for maintaining protein structure.

IR Spectroscopy and Amides

Infrared (IR) Spectroscopy aids in identifying functional groups in molecules by analysing their absorption of infrared light. Amides possess distinctive IR characteristics, important in the study of pharmaceuticals and proteins.

Key Concepts of IR Spectroscopy for Amides

• Technique Explanation:
  • Measures vibrational energy absorption to identify structural components.
  • Crucial for distinguishing amide groups in biological samples.

IR Spectral Peaks for Amides

• Characteristic Peaks:

  • C=O Stretching: Found between 1630-1690 cm$^{-1}$.
  • NH Stretching: Occurs between 3300-3500 cm$^{-1}$.

  

Variation in Amides

• Primary Amides: Contain two N-H bonds.
• Secondary Amides: Feature one N-H bond.
• Tertiary Amides: Do not have N-H bonds.

Chemical Properties Overview

• Basicity and Acidity Analysis: Amides are weaker bases relative to amines due to the resonance of the lone pair on nitrogen with the carbonyl group, limiting its availability for protonation.

• Stability and Resonance: Resonance in amides results in enhanced stability compared to other carbonyl compounds.

Common Reactions of Amides

• Hydrolysis Reactions:

  • Undergo acidic and basic hydrolysis.

    • Acid-Catalysed: Leads to protonation and formation of carboxylic acids.
    • Base-Catalysed: Results in carboxylate ions.

    

• Reduction Reactions:

  • Use of LiAlH₄ results in reduction to amines:

  $\text{RCONH}_2 + \text{LiAlH}_4 \rightarrow \text{RCH}_2\text{NH}_2$

• Comparison Table: Reaction Type vs. Observations:

  Reaction Type	Example	Key Observations
  Hydrolysis	Acidic and basic	Differences in rate
  Reduction	Using LiAlH₄	To amines

Synthesis of Amides

• Overview: Amides can be synthesised by reacting carboxylic acids with amines in the presence of an acid catalyst.
  • Example Reaction: Carboxylic Acid + Amine → Amide (with Acid Catalyst)

Synthesis Using Acid Chlorides

• Detailed Steps:
  • Step 1: Acid chloride reacts with an amine.
  • Step 2: Formation of an intermediate complex.
  • Step 3: Completion to form the amide.

Industrial Applications

Amides play a vital role in the synthesis of polymers like nylon, which are important across various industrial sectors.

Practice Synthesis Questions

Question 1: What product would be formed from the reaction of benzoyl chloride with methylamine? Solution: N-methylbenzamide would be formed as the methyl group from methylamine attaches to the nitrogen, and the carbonyl group from benzoyl chloride forms the amide linkage.

Question 2: Explain how to convert butanoic acid to butanamide. Solution: First, convert butanoic acid to butanoyl chloride using SOCl₂. Then react butanoyl chloride with ammonia to form butanamide.

Question 3: Predict the product when ethanamide undergoes hydrolysis in acidic conditions. Solution: Ethanamide would hydrolyse to form ethanoic acid and ammonium ions.

Amides in Biological Systems

Introduction to Amides in Biological Systems

• Role: Amides connect amino acids to form proteins via peptide bonds.
  • Essential in biochemistry.

Influence on Protein Folding and Stability

• Amide linkages assist in ensuring protein stability.
• Supports structures like alpha-helices and beta-sheets.

Examples of Amides in Proteins

• Haemoglobin

  • Amide bonds uphold its quaternary structure.

  

Amides and Environmental Impacts

• Biodegradability and Ecosystem Interaction:
  • Determines natural decomposition of amides. Extended presence can impose negative effects on aquatic and terrestrial environments.

• Pollution Sources:

  • Industrial and agricultural practices are major contributors.

• Environmental Consequences:

  • Potential to cause algal blooms and diminished soil fertility.

Mitigation Strategies

• Effective industrial waste management.
• Employ phytoremediation to absorb and decompose amides.