Study Notes on Carboxylic Acids, Amines, and Amides

CHAPTER 9 Carboxylic Acids, Amines, & Amides

General Overview

• Organic compounds are categorized into families based on distinct functional groups.
• A functional group is defined as an atom, group of atoms, or bond that imparts specific physical and chemical properties to a compound.

Carboxylic Acids

Structure of Carboxylic Acids

• Carboxylic acids contain a carboxyl functional group (-COOH) attached to a hydrocarbon (alkyl group) part.
• The carboxyl group consists of:
  • A carbonyl group (C=O)
  • A hydroxyl group (-OH)
• The general depiction of the carboxyl group includes its notation as “COOH” or “CO2H.”

General Structure Representation

• Chemists typically represent the general structure of a carboxylic acid using the letter “R” to denote an alkyl group or any organic group.

Example of Carboxylic Acid: Acetic Acid

• Acetic acid: Condensed structural formula is shown.
  • White vinegar composition: 95% water and 5% acetic acid.
  • Hydrocarbon part (R): Methyl group (CH₃).
  • Ball-and-stick model description:
  • Black sphere = carbon
  • Red sphere = oxygen
  • White sphere = hydrogen

Naming Carboxylic Acids Using IUPAC System

1. Find and Name the Parent Chain:

   • Longest continuous carbon chain containing the carbonyl carbon.
   • Count all carbon atoms, including the carbonyl carbon.
   • Replace the suffix “-e” of the respective alkane with “-oic acid.”
   • Example:
     • Parent chain with three carbons is propanoic acid (from propane).

2. Name Any Alkyl Group Substituents:

   • Use the same methodology as hydrocarbons for naming.

3. Determine Alkyl Group Attachment Point:

   • Assign position numbers to the parent carbons starting from the carbonyl carbon.
   • Assign numbers to substituents accordingly.

4. Construct the Final Name:

   • Place alkyl group names in alphabetical order with position numbers.
   • Include prefixes (di, tri, tetra) for identical substituents if applicable.
   • Example: 3-methylbutanoic acid (with a methyl substituent).

Example Naming Process

• Given a structure, find the following:
  1. CH3CH2COOH:
  • Parent chain: hexanoic acid
  • Alkyl group: methyl
  • Substituent position: 4
  • Final Name: 4-methylhexanoic acid.

Water Solubility of Carboxylic Acids

• Water solubility is influenced by the ability of the compound to interact with water.
• Carboxylic acids attract water through hydrogen bonding and dipole-dipole interactions.
• Small carboxylic acids show significant water solubility that decreases as the nonpolar hydrocarbon region increases.

Reaction of Carboxylic Acids with Water

• Carboxylic acids are acids as they can donate H in reactions.

• The reaction transfers a proton from the -OH group of the carboxylic acid to water, forming a carboxylate ion (A form that carries a -1 charge).

  • Carboxylate ion = Acid form (carboxylic acid) + Base form (carboxylate anion)

• Example: Ethanoic acid in water:

  • Carboxylate ion is formed by changing “-ic acid” to “-ate ion”:
  • Ethanoic acid → Ethanoate ion.

Henderson-Hasselbalch Equation

• Used for predicting relative amounts of acid and base forms in solution based on the pH.
• Example: Butanoic acid with pKa ~ 4.8 shows that a physiological pH (~7.4) would lead to a prevalence of the base form (butanoate ion).

Neutralization Reactions of Carboxylic Acids

• Carboxylic acids react with hydroxide compounds (OH−) in a neutralization reaction producing water and carboxylic acid salts.
• Examples:
  • Propanoic acid + NaOH forming sodium propanoate (water soluble if R has <12 C).
  • Salts of carboxylate ions are more water soluble than carboxylic acids.

Esterification: Carboxylic Acid with Alcohol

• An ester results when a carboxylic acid reacts with an alcohol, producing water in the process.
  • General Reaction:
    $ext{Carboxylic Acid} + ext{Alcohol} <br /> ightarrow ext{Ester} + ext{Water}$
  • Notation: R (carboxylic acid) and R' (alcohol).

Hydrolysis of Amides

• Reverse of the amide reaction to produce a carboxylic acid and an amine (or ammonia).
  • Hydrolysis occurs with heat and acid catalyst.

Decarboxylation Reaction

• Removing a carboxyl group (COOH) and substituting a hydrogen atom.
• Important in biological processes like the citric acid cycle.
  • General Decarboxylation:
    $ext{Carboxylic Acid} </li></ul></li> </ul> <h4 id="ightarrowexthydrogenextco_2dd">ightarrow ext{Hydrogen} + ext{CO}_2$

    Amines

    Structure of Amines

    • Amines feature a nitrogen atom with a lone pair and single bonds to R (hydrocarbon groups) or hydrogen.
    • Classifications of amines:
      • Primary (1º): one R group.
      • Secondary (2º): two R groups.
      • Tertiary (3º): three R groups.

    Naming Amines

    • Find the longest carbon chain associated with the nitrogen to determine the parent chain and apply similar rules as with alkanes.
    • For amines with more than two carbons, position numbers to show attachment to nitrogen must be assigned.

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    Amides

    Structure of Amides

    • Contain a carbonyl group (C=O) attached to a nitrogen atom that’s bonded to the carbonyl carbon.
    • Example: Ethanamide with structural representations provided.

    Naming Amides

    1. Find and Name Parent Chain: Same approach as carboxylic acids, converting -e to -amide.
       • Example: Propanoic acid becomes propanamide.
    2. Name Alkyl Group Substituents: Similar procedure by indicating positions and using N- for nitrogen attachments.
    3. Construct Amide Name by listing any substituents alphabetically with the parent name.
       • For example: N-methylpropanamide.

    Formation of Amides

    • Formed via the reaction of carboxylic acids with ammonia or primary/secondary amines.
    • Illustrative reactions shown for clarity of the process.

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    Heterocyclic Compounds

    Overview of Heterocycles

    • Defined as cyclic compounds containing atoms other than carbon (e.g., nitrogen, oxygen).
    • Common examples include pyridine and purine.

    Functional and Physiological Roles

    • Heterocycles play critical roles in biological systems, and notable examples are nicotine and adenosine triphosphate (ATP), essential for energy transfer in biological molecules.

    Properties of Amines

    • Smaller amines possess strong odors and physiological roles include toxicity or biological activity.
    • Physiologically active amines are referred to as alkaloids.
      • Examples: Morphine, heroin, etc.