Carboxylic Acids and Nitriles Notes

Overview of Carboxylic Acids and Nitriles

  • Key Topics Covered:
    • Naming of carboxylic acids and nitriles
    • Structure and properties of carboxylic acids
    • Biological acids and the Henderson-Hasselbalch equation
    • Substituent effect on acidity
    • Preparation of carboxylic acids
    • Reactions of carboxylic acids
    • Chemistry of nitriles
    • Spectroscopy of carboxylic acids and nitriles

Carboxylic Acid Structure

  • Carboxylic acids contain a carboxy group (−COOH)(-COOH).
  • The structure can be simplified as RCOOHRCOOH or RCO2HRCO_2H.
  • The central carbon in the carboxy group is:
    • Doubly bonded to one oxygen atom (C=O)
    • Singly bonded to another oxygen atom (O-H)

Bonds in Carboxylic Acids

  • The C-O single bond in carboxylic acids is shorter than that in alcohols due to increased electronegativity of oxygen.
  • Bonds in carboxylic acids are polar because:
    • Oxygen is more electronegative than carbon and hydrogen, resulting in dipole-dipole interactions.

Nitriles

  • Nitriles contain a cyano group (C≡N) connected to an alkyl group.
  • Electrophilic nature of the carbon in cyano groups makes nitriles susceptible to nucleophilic attacks.

Naming Carboxylic Acids (IUPAC)

  • The IUPAC naming convention involves:
    • Identifying the longest carbon chain with the COOH group.
    • Changing the e ending of the parent alkane name to -oic acid if it's attached to a chain.
    • For cyclic compounds, name the ring and include "carboxylic acid."
    • Number the chain or loop to position the COOH at C1 (omit from name).
  • Compounds containing two carboxyl groups are termed diacids.

Common Names of Carboxylic Acids

  • Metal salts of carboxylic acids are formed in reactions and named by combining:
    • Metal name
    • Carboxylate anion name
    • For example: Sodium acetate & potassium propanoate.

Nomenclature of Nitriles

  • Nitriles are named as alkane derivatives:
    • Identify the longest chain that contains the cyano group (C≡N) and add nitrile to the alkane name.
    • The carbon in the cyano group is placed at C1 (omit from the name).
    • Common names are derived from parent carboxylic acids by replacing -ic acid with -onitrile.

Hydrogen Bonding in Carboxylic Acids

  • Carboxylic acids can exhibit hydrogen bonding due to polar C=O and O-H bonds.
  • They often exist as dimers linked by hydrogen bonds.

Physical Properties of Carboxylic Acids

  • Carboxylic acids feature strong intermolecular forces, resulting in:
    • Higher boiling points compared to similar alcohols and hydrocarbons.
    • Increased water solubility due to their polarity.

Acidity of Carboxylic Acids

  • The acidic character is primarily due to the polar O-H bond with a pKa around 5.
  • Stronger acids have more stable conjugate bases (carboxylate anions) after deprotonation.

Inductive Effects in Carboxylic Acids

  • The acidity increases with a greater number of electronegative substituents.
  • The proximity of these substituents to the carboxyl group significantly affects acid strength.
  • Example of acidity ranking due to substituents:
    • pK_a: 0.9 < 1.3 < 2.6 < 2.8 (increased acidity with increasing electronegative Cl atoms).

Substituents and Their Effects on Acidity

  • Common effects are influenced by resonance and inductive effects:
    • Electro-withdrawing groups enhance acidity.
    • Closer proximity of these groups to the -COOH increases their acidic strength.

Organic Extraction Techniques

  • Organic extraction separates compounds based on solubility and acid-base principles:
    • Two immiscible liquids create separate layers; separation occurs using a separatory funnel.
    • Example: To separate benzoic acid from cyclohexanol, utilize an aqueous NaOH solution to dissolve the acid in the aqueous phase.

Practice Problems

  • Provide IUPAC names for given metal salts and nitrile compounds.
  • Rank acidity of various carboxylic acids based on their structure and substituents.
  • Conduct practices on organic extraction methods related to carboxylic acids.

Interesting Carboxylic Acids

  • Formic acid - name derived from Latin for "ant"; known for its stinging properties.
  • Acetic acid - known as the sour component in vinegar, used industrially, often called glacial acetic acid.
  • Hexanoic acid - foul smell often associated with dirty socks; also known as caproic acid, related to goats.