For acetaldehyde (CH3CHO), write the Lewis structure. Write the hybridization and geometry of each carbon. Draw its 3D structure and write the bond angles (approximately).
The Correct Answer and Explanation is:
Correct Answer:
- Lewis Structure of Acetaldehyde (CH₃CHO):
mathematicaCopyEdit H H
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H–C–C=O
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H
Expanded:
- Carbon 1 (CH₃): forms 3 single bonds with hydrogen and 1 single bond with the adjacent carbon.
- Carbon 2 (C=O): forms 1 single bond with CH₃, 1 double bond with oxygen, and 1 single bond with hydrogen.
- Hybridization and Geometry:
- Carbon 1 (CH₃ group): sp³ hybridized; geometry is tetrahedral.
- Carbon 2 (carbonyl carbon): sp² hybridized; geometry is trigonal planar.
- Bond Angles:
- Around CH₃ carbon (sp³): approximately 109.5°.
- Around carbonyl carbon (sp²): approximately 120°.
- 3D Structure (Description):
- The methyl group (CH₃) is tetrahedral with hydrogens positioned to minimize repulsion.
- The carbonyl carbon (C=O) lies in a trigonal planar arrangement with the double bond to oxygen and single bonds to the methyl group and hydrogen, forming roughly 120° angles.
Explanation:
Acetaldehyde (CH₃CHO) is a simple aldehyde composed of two carbon atoms, four hydrogen atoms, and one oxygen atom. The molecule features a carbonyl group (C=O) bonded to a methyl group (CH₃) and a hydrogen atom.
The Lewis structure is constructed by placing the atoms in their typical bonding patterns. The methyl carbon forms three single bonds with hydrogen atoms and one single bond with the adjacent carbon, requiring a total of four sigma bonds. This carbon uses sp³ hybrid orbitals, resulting in a tetrahedral geometry with bond angles near 109.5°.
The carbon of the carbonyl group forms a double bond with oxygen, a single bond with the methyl carbon, and a single bond with a hydrogen atom. This atom uses sp² hybridization, generating three electron domains arranged in a trigonal planar geometry. Bond angles around this carbon are approximately 120°.
The oxygen atom in the carbonyl group holds two lone pairs and forms a double bond with carbon. This results in a bent electron arrangement but a linear bonding shape relative to the carbon.
The 3D shape shows the CH₃ group with a tetrahedral arrangement of hydrogen atoms, while the carbonyl group lies flat in a plane. These geometries are dictated by electron repulsion principles described in VSEPR theory.
This configuration gives acetaldehyde its characteristic planar region around the carbonyl and a pyramidal CH₃ group, allowing it to participate in various chemical reactions, particularly as an electrophile due to the polarized carbonyl group.
