Which has apyramidal structure?

Options

A. Trimethylamine
B. Methanol
C. Acetylene
D. Water

Answer

To determine which compound has a pyramidal structure, we will analyze the structures of the given compounds: trimethylamine, water, methanol, and acetylene.

### Step-by-Step Solution:

1. **Understanding Molecular Geometry**:
- Molecular geometry is determined by the arrangement of atoms in a molecule, which is influenced by the number of bonding pairs and lone pairs of electrons around the central atom.

2. **Analyzing Water (H2O)**:
- Water has two hydrogen atoms bonded to oxygen and two lone pairs on oxygen.
- The molecular geometry is bent due to the repulsion between the lone pairs, resulting in a tetrahedral electron geometry but a bent molecular shape.

3. **Analyzing Methanol (CH3OH)**:
- Methanol has one hydroxyl group (-OH) and three hydrogen atoms bonded to carbon.
- The oxygen atom has two lone pairs and forms a tetrahedral shape, but the presence of the hydroxyl group gives it a bent shape as well.

4. **Analyzing Acetylene (C2H2)**:
- Acetylene has a linear structure due to the triple bond between the two carbon atoms.
- There are no lone pairs affecting the geometry, and thus it does not have a pyramidal structure.

5. **Analyzing Trimethylamine ((CH3)3N)**:
- Trimethylamine has three methyl groups attached to nitrogen, which has one lone pair.
- The nitrogen atom has a total of four regions of electron density (three bond pairs and one lone pair).
- The presence of the lone pair causes the bond angles to be less than the ideal tetrahedral angle (109.5°), resulting in a trigonal pyramidal shape.

6. **Conclusion**:
- Among the compounds analyzed, trimethylamine is the only one that exhibits a pyramidal structure due to the presence of a lone pair on nitrogen, which influences the geometry.

### Final Answer:
Trimethylamine has a pyramidal structure.

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