Following the rule that each atom of carbon, oxygen and nitrogen bonds in such a way as to achieve a complete outer shell of eight valence electrons, the number of unshared pairs of electrons (lone pairs) in this molecule will be A. 7
B. 6
C. 5
D. 8

Question

BlackTom AI · Accepted Answer

Oxygen atoms in neutral organic functional groups carry two lone pairs (four electrons) and an sp3 amine nitrogen carries one lone pair; carbon atoms that satisfy the octet with four bonds have no lone pairs.

1) Relevant concepts
- Oxygen (6 valence electrons) achieves an octet by forming two bonding pairs (two single bonds or one double bond counts as two bonding pairs) and retaining two lone pairs.
- Nitrogen (5 valence electrons) in an amine (three single bonds) has one lone pair.
- Carbon (4 valence electrons) normally forms four bonds and has no lone pairs when its octet is satisfied.

2) Identify the heteroatoms in the drawn molecule
- Ether ring oxygen: 1 O
- Carboxylic acid group: 2 O (one carbonyl O and one hydroxyl O)
- Primary amine: 1 N
Total heteroatoms of interest: 3 oxygens + 1 nitrogen.

3) Count lone pairs step by step
- Ether oxygen: bonded to two carbons (two single bonds → two bonding pairs). Needs two lone pairs to reach octet → 2 lone pairs.
- Carbonyl oxygen (C=O): double bond counts as two bonding pairs → needs two lone pairs → 2 lone pairs.
- Hydroxyl oxygen (–OH): bonded to C and H (two single bonds → two bonding pairs) → needs two lone pairs → 2 lone pairs.
- Amine nitrogen (–NH2): bonded to one carbon and two hydrogens (three single bonds → three bonding pairs) → needs one lone pair → 1 lone pair.

4) Arithmetic (intermediate steps)
- O atoms: 3 × 2 lone pairs = 6 lone pairs
- N atom: 1 × 1 lone pair = 1 lone pair
- Total = 6 + 1 = 7 lone pairs

5) Why other choices are incorrect
- B (6): counts only the oxygens’ lone pairs and omits the nitrogen’s lone pair.
- C (5): understates lone pairs (no clear structural basis).
- D (8): overcounts by one pair (no atom in the neutral structure contributes an extra lone pair).

Conclusion: The molecule contains 7 unshared (lone) pairs of electrons, so answer A is correct.

Following the rule that each atom of carbon, oxygen and nitrogen bonds in such a way as to achieve a complete outer shell of eight valence electrons, the number of unshared pairs of electrons (lone pairs) in this molecule will be A. 7 B. 6 C. 5 D. 8单项选择题

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