Ethers Structure

8 MCQs9-step worked example
Source: NCERT BiomoleculesPYQ coverage: NEET 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

Structure of Ethers — What NEET Expects You to Know

Ethers are organic compounds with the general formula R–O–R′, where R and R′ are alkyl or aryl groups bonded to an oxygen atom. The oxygen in an ether carries two lone pairs and adopts an approximately sp³ hybridisation geometry, similar to water. The C–O–C bond angle in dimethyl ether is about 111.7° — slightly larger than the tetrahedral angle of 109.5° — due to repulsion between the two bulky alkyl groups (NCERT Class 12 Chemistry, Chapter 7, Part 2, page 18).

Nomenclature — two systems you must know:

  1. Common naming: name the two alkyl/aryl groups alphabetically, followed by "ether." CH₃–O–C₂H₅ is ethyl methyl ether. When both groups are identical, use the prefix "di-": CH₃–O–CH₃ is dimethyl ether.
  2. IUPAC naming: ethers are named as alkoxyalkanes. The smaller alkyl group + oxygen becomes the alkoxy prefix; the larger chain is the parent alkane. CH₃–O–C₂H₅ is methoxyethane.

Classification:

  • Simple (symmetrical) ethers: both R groups identical (e.g., diethyl ether, C₂H₅–O–C₂H₅).
  • Mixed (unsymmetrical) ethers: R groups differ (e.g., ethyl methyl ether).

Physical properties relevant to NEET:

  • Ethers have much lower boiling points than isomeric alcohols because ethers cannot form hydrogen bonds with themselves (no O–H bond). However, ethers CAN accept hydrogen bonds from water, making lower ethers (like dimethyl ether and diethyl ether) slightly soluble in water.
  • Ethers are relatively unreactive — the C–O bond is difficult to cleave under ordinary conditions, which is why diethyl ether is widely used as a solvent.

Common confusion: students sometimes conflate the bond angle and hybridisation of ethers with that of epoxides (cyclic ethers with ~60° angles and significant ring strain). The C–O–C angle in open-chain ethers is near tetrahedral; in epoxides it is forced to ~60° by the three-membered ring.

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

The general formula of an ether is:

MCQ 2Easy RecallPractice

The hybridisation of oxygen in dimethyl ether is:

MCQ 3Easy RecallPractice

The IUPAC name of CH₃–O–C₂H₅ is:

MCQ 4Direct ApplicationPractice

Which of the following is a symmetrical ether?

MCQ 5Direct ApplicationPractice

Diethyl ether has a much lower boiling point than 1-butanol, despite having similar molecular masses. The primary reason is:

MCQ 6Direct ApplicationPractice

Lower ethers like diethyl ether are slightly soluble in water because:

MCQ 7Concept TrapPractice

The C–O–C bond angle in dimethyl ether (~111.7°) is slightly larger than the ideal tetrahedral angle (109.5°). The most likely reason is:

MCQ 8Concept TrapPractice

A student claims that the C–O–C bond angle in ethylene oxide (an epoxide) is similar to that in dimethyl ether. Which statement correctly identifies the error?

Worked Example

  1. 1

    Given

    - Molecular formula: C₄H₁₀O - The compound is an ether (confirmed by absence of reaction with Na) - Both alkyl groups on oxygen are identical (symmetrical ether)

  2. 2

    Required

    - Structural formula - Common name - IUPAC name - Approximate C–O–C bond angle

  3. 3

    Concept

    An ether with formula R–O–R (symmetrical) must partition the non-oxygen atoms equally between the two R groups. The oxygen in an open-chain ether is sp³ hybridised, giving a bond angle near the tetrahedral value.

  4. 4

    Formula / Principle

    - General formula of ether: R–O–R′ - For C₄H₁₀O with identical groups: C₄H₁₀O = R–O–R, so 2R + O = C₄H₁₀O - Each R must account for C₂H₅ (ethyl group)

  5. 5

    Substitution

    - C₄H₁₀O → C₂H₅–O–C₂H₅ - Common name: the two alkyl groups are both ethyl → diethyl ether - IUPAC name: smaller group = ethyl → ethoxy prefix; larger chain = ethane → ethoxyethane

  6. 6

    Calculation

    No arithmetic calculation is needed here. The structural deduction is: - Total carbons = 4, split equally → 2 carbons per alkyl group → C₂H₅ each - Hydrogen count check: 2 × (C₂H₅) + O = C₄H₁₀O ✓

  7. 7

    Final answer

    - **Structural formula:** C₂H₅–O–C₂H₅ - **Common name:** Diethyl ether - **IUPAC name:** Ethoxyethane - **C–O–C bond angle:** approximately 112° (slightly greater than tetrahedral 109.5° due to steric repulsion between the two ethyl groups; oxygen is sp³ hybridised)

  8. 8

    Common trap

    A common confusion is writing "ethoxymethane" or choosing the larger group as the alkoxy prefix. IUPAC convention: the smaller group becomes the alkoxy prefix, the larger chain is the parent alkane. When both groups are identical, either can be the prefix — but the systematic name is ethoxyethane, not "diethyl ether" (which is the common name only).

  9. 9

    Similar NEET-style question

    An ether with molecular formula C₅H₁₂O gives two different alkyl groups upon cleavage with HI. One fragment is methanol and the other is 2-bromopropane. Write the structural formula of the ether and give its IUPAC name. *(Answer: CH₃–O–CH(CH₃)₂, 2-methoxypropane)* ---

Before solving, remember these

Key Fact

Nitric acid — Ostwald's process and properties

Industrial manufacture (Ostwald's process): (1) 4NH₃ + 5O₂ → 4NO + 6H₂O (Pt/Rh catalyst, 500 K, 9 bar); (2) 2NO + O₂ → 2NO₂; (3) 3NO₂ + H₂O → 2HNO₃ + NO. HNO₃ is a strong oxidising acid. Concentrated HNO₃ passivates Fe, Al (oxide layer). Aqua regia (3:1 HCl:HNO₃ conc) dissolves noble metals (Au, Pt).

-- NCERT Class 12 Chemistry, Ch. 7, p. 9

Formulas

pKa of carboxylic acid

Stronger acid than phenol due to more effective resonance over two equivalent oxygens. EWG substituents (Cl, NO2) increase acidity.

SymbolQuantitySI Unit
pKa-log Ka-

Valid when

  • Aqueous solution
  • α-substituent effects strongest

pKa of phenol vs aliphatic alcohol

Phenols ~10⁶× more acidic than aliphatic alcohols due to resonance stabilisation of phenoxide ion. Electron-withdrawing substituents lower pKa further.

SymbolQuantitySI Unit
pKa-log Ka-

Valid when

  • Aqueous solution
  • Substituent effects shift values

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Oxidation product depends on reagent strength

Category: Organic Reaction Conditions

1° alcohol: PCC/PDC → aldehyde (stops). KMnO4/K2Cr2O7 in acidic → carboxylic acid (continues). 2° alcohol: any oxidiser → ketone. 3° alcohol: not oxidised by ordinary reagents.

When it triggers

Question gives 1° alcohol oxidation with specified reagent.

How to avoid

PCC, PDC, Swern, DMP: mild → stop at aldehyde. KMnO4, K2Cr2O7, CrO3, jones: strong → carboxylic acid. Reagent choice matches desired product.

Past Year Questions

20 questions from NEET 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2024Revised key

Given below are two statements: Statement I : Aniline does not undergo Friedel-Crafts alkylation reaction. Statement II : Aniline cannot be prepared through Gabriel synthesis . In the light of the above statements, choose the correct answer from the options given below:

1Both statement I and Statement II are true
2Both Statement I and Statement II are false
3Statement I is correct but Statement II is false
4Statement I is incorrect but Statement II is true
NTA Answer: Option 1(revised_final)
NEET 2024Revised key

Fehling’s solution ‘A’ is

1aqueous copper sulphate
2alkaline copper sulphate
3alkaline solution of sodium potassium tartrate (Rochelle’s salt)
4aqueous sodium citrate
NTA Answer: Option 1(revised_final)
NEET 2022

Given below are two statements: Statement I: In Lucas test, primary, secondary and tertiary alcohols are distinguished on the basis of their reactivity with conc. HCl + ZnCl , known as Lucas Reagent. 2 Statement II: Primary alcohols are most reactive and immediately produce turbidity at room temperature on reaction with Lucas Reagent. In the light of the above statements, choose the most appropriate answer from the options given below:

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 4(final)
NEET 2021

Match List-I with List-II List-I List-II CO, HCI (a) (i) Hell-Volhard-Zelinsky Anhyd. AlCl/ Cu3Cl reaction O R — C — CH + (b) (ii) Gattermann-Koch 3 NaOX reaction R — CH — OH (c) (iii) Haloform reaction 2 +R′ COOH Conc. HSO 2 4 (d) R — CH COOH (iv) Esterification 2 ( II) X /Red P 2 (ii) HO 2 Choose the correct answer from the options given below.

1(a) - (ii), (b) - (iii), (c) - (iv), (d) - (i)
2(a) - (iv), (b) - (i), (c) - (ii), (d) - (iii)
3(a) - (iii), (b) - (ii), (c) - (i), (d) - (iv)
4(a) - (i), (b) - (iv), (c) - (iii), (d) - (ii)
NTA Answer: Option 1(final)

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