🔥 Structures of Functional Groups (Alcohols, Phenols & Ethers)

1️⃣ Alcohols

In alcohols, the –OH group is connected to a carbon atom through a sigma (σ) bond. This bond is made by the overlap of:

  • sp^3 hybridised orbital of carbon
  • sp^3 hybridised orbital of oxygen

🧪 Example: Methanol structure

The bond angle in alcohols is slightly less than the tetrahedral angle (about 109°28′). Why? 🤔

  • Due to repulsion between unshared electron pairs (lone pairs) on oxygen

2️⃣ Phenols

In phenols, the –OH group is attached to an sp2 hybridised carbon of an aromatic ring 🧪

⚛️ C–O bond length in phenol = 136 pm (shorter than in methanol)

Reasons:

  1. There’s partial double bond character 💫 due to conjugation between lone pair on oxygen and the aromatic ring
  2. Oxygen is bonded to an sp^2 hybridised carbon

3️⃣ Ethers

Ethers have an oxygen atom bonded to two alkyl or aryl groups. The oxygen has:

  • 2 bond pairs
  • 2 lone pairs

These 4 electron pairs arrange in a tetrahedral geometry 🧬

⚠️ But the bond angle is a bit more than 109°28′ due to repulsion between bulky R groups (alkyl groups).

📏 C–O bond length in ethers = 141 pm (similar to alcohols)

💡 Naming Ethers

In the IUPAC system, ethers are treated as derivatives of hydrocarbons where a hydrogen is replaced by:

  • –OR (alkyl group)
  • –OAr (aryl group)

How to name:

  • Pick the larger R group as the main chain
  • Name the smaller group as a prefix (e.g., ethoxy, methoxy)

🔁 If both groups are the same, use the prefix “di-“

👉 Example: C₂H₅OC₂H₅ is called diethyl ether

📸 Visuals

  • Methanol
  • Phenol
  • Methoxymethane

(These are usually shown as molecular diagrams for structure clarity.)

🧠 In-Text Practice – IUPAC Naming Examples

  1. 4-Chloro-2,3-dimethylpentan-1-ol
  2. 2-Ethoxypropane
  3. 2,6-Dimethylphenol
  4. 1-Ethoxy-2-nitrocyclohexane

🌟 High-Yield NEET Concepts

  • 📏 Bond angles and geometry of –OH and –OR groups
  • 🔄 Resonance in phenols and its effect on bond length
  • 📐 Difference in hybridisation: sp3 (alcohols) vs sp2 (phenols)
  • 🧪 Nomenclature rules for ethers in IUPAC
  • 🔬 Structural characteristics and electron pair repulsions in functional groups