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Ethers: structure: NEET MCQs with answers

49 questions on this topic of Organic Compounds Containing Oxygen (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.

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easy

1. Ethers can act as Lewis bases because the oxygen atom:

  1. Has a formal positive charge in the ground state
  2. Is sp hybridized with a high percentage of s-character
  3. Can expand its octet by utilizing vacant 3d orbitals
  4. Possesses two unshared electron pairs available for coordination
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Answer: (D) Possesses two unshared electron pairs available for coordination

The oxygen atom in ethers contains two lone pairs of non-bonding electrons in sp³-like hybrid orbitals. These electron pairs can be donated to electron-deficient species (Lewis acids such as BF₃ or Grignard reagents) to form coordinate bonds.

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2. The C-O-C bond angle in dimethyl ether is about 111.7°, slightly greater than the tetrahedral angle, because of:

  1. Hydrogen bonding
  2. Repulsion between the two bulky methyl groups
  3. sp hybridisation of oxygen
  4. Absence of lone pairs on oxygen
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Answer: (B) Repulsion between the two bulky methyl groups

Oxygen in ethers is sp³ hybridised, but repulsive interaction between the two bulky alkyl groups opens the angle beyond 109.5°.

NCERT Class 12

hard

3. Consider the following three bonds in an ether molecule R-O-R': I. C-O σ bond II. C-H σ bond of the α-carbon III. O lone pair coordinate bond What is the nature of the overlap forming the C-O σ bond in diethyl ether?

  1. 2p(C) - 2p(O)
  2. sp³(C) - 2p(O)
  3. sp²(C) - sp³(O)
  4. sp³(C) - sp³(O)
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Answer: (D) sp³(C) - sp³(O)

In diethyl ether, both the ethereal oxygen atom and the attached alkyl carbon atoms are sp³ hybridized. The C-O σ bond is formed by the axial overlap between an sp³ hybrid orbital of carbon and an sp³ hybrid orbital of oxygen.

medium

4. Consider the molecular structure of methoxybenzene (anisole). Why is the C(aromatic)-O bond length shorter than the C(methyl)-O bond length?

  1. Due to greater steric hindrance around the aromatic ring
  2. Due to resonance conjugation between the oxygen lone pair and the phenyl ring
  3. Due to complete transfer of electrons from the methyl group to oxygen
  4. Due to sp² hybridization of the methyl carbon
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Answer: (B) Due to resonance conjugation between the oxygen lone pair and the phenyl ring

In methoxybenzene, one of the lone pairs of oxygen undergoes resonance delocalization with the π-electron cloud of the benzene ring. This imparts partial double bond character to the C(aromatic)-O bond, shortening it relative to the single C(sp³)-O bond.

easy

5. Which of the following compounds is a symmetrical (simple) aromatic ether?

  1. Ethoxybenzene
  2. Diphenyl ether
  3. Methoxybenzene
  4. Benzyl methyl ether
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Answer: (B) Diphenyl ether

Diphenyl ether (C₆H₅-O-C₆H₅) contains two identical aromatic groups (phenyl rings) attached to the ethereal oxygen atom, classifying it as a simple or symmetrical ether. The others contain two different organic groups attached to oxygen.

hard

6. An organic ether 'X' has the molecular formula C₄H₈O. It does not decolorize bromine water and contains a three-membered ring with an oxygen atom. Which of the following statements about 'X' is correct?

  1. It contains only primary and tertiary carbon atoms.
  2. It can exist as a pair of cis-trans (geometrical) isomers if it is 2,3-dimethyloxirane.
  3. It must possess at least one sp² hybridized carbon atom.
  4. The C-O-C bond angle inside the ring is approximately 109.5°.
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Answer: (B) It can exist as a pair of cis-trans (geometrical) isomers if it is 2,3-dimethyloxirane.

The formula C₄H₈O has a degree of unsaturation of 1. Since it does not decolorize bromine water, it has no C=C double bond. For a three-membered cyclic ether (oxirane ring), 2,3-dimethyloxirane has two chiral centers with identical substituents and exhibits cis-trans isomerism (cis is meso, trans is a pair of enantiomers). The ring angle is heavily strained (~60°), not 109.5°.

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7. Compare the C-O bond length in methoxymethane (dimethyl ether) with the C(aromatic)-O bond length in methoxybenzene (anisole):

  1. The C-O bond length in methoxymethane is shorter due to hyperconjugation.
  2. The C-O bond length in methoxybenzene is longer due to steric hindrance of the benzene ring.
  3. Both C-O bond lengths are identical because both involve an sp³ oxygen.
  4. The C(aromatic)-O bond length in methoxybenzene is shorter due to resonance.
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Answer: (D) The C(aromatic)-O bond length in methoxybenzene is shorter due to resonance.

In methoxybenzene, the unshared electron pair of oxygen is conjugated with the aromatic ring, giving the C(aromatic)-O bond partial double bond character. Additionally, the carbon of the benzene ring is sp² hybridized, which makes this bond shorter (136 pm) than the sp³ C-O bond in dialkyl ethers (141 pm).

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8. The C-O-C bond angle in methoxymethane is 111.7°. How many σ-bonds and π-bonds are present in one molecule of methoxymethane?

  1. 6 σ-bonds and 0 π-bonds
  2. 7 σ-bonds and 0 π-bonds
  3. 8 σ-bonds and 1 π-bond
  4. 8 σ-bonds and 0 π-bonds
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Answer: (D) 8 σ-bonds and 0 π-bonds

In methoxymethane (CH₃-O-CH₃), each methyl group has three C-H σ-bonds (giving 6 C-H σ-bonds) and there are two C-O σ-bonds. This gives a total of 6 + 2 = 8 σ-bonds and 0 π-bonds.

easy

9. According to VSEPR theory, the molecular geometry (shape) of methoxymethane excluding lone pairs is described as:

  1. Linear
  2. Bent (V-shaped)
  3. Trigonal planar
  4. Tetrahedral
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Answer: (B) Bent (V-shaped)

Methoxymethane has an AB₂E₂ type arrangement around the central oxygen atom (two bond pairs and two lone pairs). While the electron-pair geometry is tetrahedral, the actual molecular shape formed by the nuclei is bent or V-shaped.

medium

10. Given below are two statements: Assertion (A): The dipole moment of diethyl ether is 1.18 D, whereas the dipole moment of carbon dioxide is 0 D. Reason (R): In diethyl ether, the two polar C-O bonds are inclined to each other at an angle greater than 109.5°, preventing the two bond dipoles from canceling each other. In the light of the above statements, choose the correct answer:

  1. Both (A) and (R) are true and (R) is the correct explanation of (A)
  2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
  3. (A) is true but (R) is false
  4. (A) is false but (R) is true
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Answer: (A) Both (A) and (R) are true and (R) is the correct explanation of (A)

Diethyl ether has an angular (bent) geometry with a C-O-C bond angle greater than 109.5° due to steric repulsions between the ethyl groups. Because it is non-linear, the individual polar C-O bond moments do not point in opposite directions and do not cancel out, resulting in a net molecular dipole moment of ~1.18 D. In contrast, CO₂ is linear and its dipoles cancel completely.

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11. Which of the following ethers possesses a chiral carbon in its structure?

  1. 1-Methoxypropane
  2. 2-Methoxypropane
  3. 2-Methoxybutane
  4. 1-Ethoxypropane
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Answer: (C) 2-Methoxybutane

2-Methoxybutane has the structure CH₃-CH(OCH₃)-CH₂-CH₃. Carbon-2 is bonded to four different groups: -H, -CH₃, -OCH₃, and -CH₂CH₃, making it an asymmetric (chiral) carbon.

easy

12. In methoxymethane, the number of lone pairs of electrons present on the oxygen atom and the number of σ bonds formed by the oxygen atom are, respectively:

  1. 0 and 4
  2. 1 and 3
  3. 2 and 1
  4. 2 and 2
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Answer: (D) 2 and 2

Oxygen in methoxymethane has six valence electrons. It shares two electrons to form two single C-O σ bonds with two methyl groups, leaving two non-bonding electron pairs (lone pairs) on the oxygen atom.

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