Which of the following conversions results in the formation of a different shape around the carbon atom?

Question

BlackTom AI · Accepted Answer

Hybridization of the carbon atom determines its molecular geometry: sp (linear), sp2 (trigonal planar), sp3 (tetrahedral). Count the regions of electron density (sigma bonds + lone pairs) around the carbon to find its steric number and thus hybridization and shape.

Step-by-step for the relevant species:

1. Methanoic acid (HCOOH): the carbon is bonded to a hydrogen (σ), to an OH group (σ), and to an oxygen by a double bond (C=O: one σ + one π, but the double bond counts as one region). Total regions = 3 → steric number 3 → sp2 hybridization → trigonal planar geometry.

2. Methanol (CH3OH): the carbon is bonded to three hydrogens (3 σ) and one oxygen (σ) for a total of 4 sigma bonds → regions = 4 → steric number 4 → sp3 hybridization → tetrahedral geometry.

Because methanoic acid’s carbon is sp2 (planar) and methanol’s carbon is sp3 (tetrahedral), converting methanoic acid to methanol changes the carbon’s shape from trigonal planar to tetrahedral.

Why the other options do not change shape:
- Chloromethane (CH3Cl) → methanol (CH3OH): both carbons have four single bonds (4 σ regions) → sp3 → tetrahedral in both, so no shape change.
- Methanoic acid (HCOOH) → methanal (HCHO, formaldehyde): both have C=O plus two other single-bonded atoms (three regions) → sp2 → trigonal planar in both, so no change.
- Methanoic acid → methanoate ion (HCOO–): carbon is bonded to H and two oxygens (one of them with negative charge but overall still three regions) → sp2 → trigonal planar, so no change.
- Methane (CH4) → bromomethane (CH3Br): both are CH4-like with four σ bonds around C → sp3 → tetrahedral, so no change.

Conclusion: The conversion that results in a different carbon shape is Methanoic acid to methanol, which matches the provided correct answer.

Which of the following conversions results in the formation of a different shape around the carbon atom?单项选择题

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