Draw Lewis structure for CH3COCH3.
Label all the atoms in CH3COCH3 ?with their appropriate hybridization states.
all the bonds in CH3COCH3 ?as sigma (\sigma ) ?and pi (\pi ) ?bonds.
Indicate which orbitals overlap to form each bond.What is the bond angle in CH3COCH3 ? ?What shape would you expect? ?Is the molecule polar or nonpolar? If your answer is polar, indicate the direction of
the dipole moment.) ?Which intermolecular interactions do CH3COCH3 ?molecules have?
The Correct Answer and Explanation is:
Let’s analyze the molecule CH₃COCH₃ (acetone), step by step:
a) Lewis Structure for CH₃COCH₃:
CH₃COCH₃ is acetone, a ketone with the structure:
O
||
CH3 - C - CH3
The Lewis structure:
- Central carbon (carbonyl carbon) double-bonded to oxygen and single-bonded to two methyl groups (CH₃).
- Each H has a single bond.
- Each O has 2 lone pairs.
b) Hybridization of Atoms:
- CH₃ carbon atoms (on both ends): sp³ hybridized (4 sigma bonds: 3 C-H and 1 C-C).
- Central carbon (C=O): sp² hybridized (1 sigma bond to each CH₃ and 1 sigma + 1 pi bond to O).
- Oxygen: sp² hybridized (1 sigma bond + 1 pi bond + 2 lone pairs).
c) Bond Types (σ and π):
- C-H: σ bonds (sp³–s)
- C-C: σ bond (sp³–sp²)
- C=O: 1 σ bond (sp²–sp²), 1 π bond (p–p)
d) Overlapping Orbitals:
- C-H bonds: sp³ (C) overlaps with s (H)
- C–C bonds: sp³ (CH₃) overlaps with sp² (central C)
- C=O bond:
- σ bond: sp² (C) with sp² (O)
- π bond: p orbital (C) with p orbital (O)
e) Bond Angle and Molecular Shape:
- Central carbon: sp² → trigonal planar → bond angles ~120°
- Methyl groups: tetrahedral → ~109.5°, but slightly distorted due to C=O pull
f) Polarity and Dipole Moment:
Polar molecule.
- The C=O bond is highly polar due to the electronegative oxygen.
- Dipole points from the carbon toward the oxygen.
- Although CH₃ groups are symmetrical, they cannot cancel the C=O dipole.
g) Intermolecular Forces:
- Dipole–dipole interactions (due to polar C=O bond)
- London dispersion forces (present in all molecules)
- No hydrogen bonding (no H directly bonded to O or N)
300-word Explanation:
Acetone (CH₃COCH₃) is the simplest ketone, with a central carbon double-bonded to an oxygen atom and single-bonded to two methyl groups. In drawing its Lewis structure, each atom obeys the octet rule. The central carbon forms three sigma bonds: two with carbon atoms from methyl groups and one with oxygen. Additionally, a pi bond exists between the central carbon and oxygen due to the double bond.
Hybridization helps us understand the geometry and bonding. The methyl carbons are sp³ hybridized because they each form four sigma bonds—three with hydrogen atoms and one with the carbonyl carbon. The central carbon is sp² hybridized, forming three sigma bonds (two C–C and one C=O sigma) and one pi bond with oxygen. Oxygen also uses sp² hybridization for bonding and holds two lone pairs in unhybridized p orbitals.
The geometry around the central carbon is trigonal planar, leading to bond angles of approximately 120°, while the methyl groups have tetrahedral arrangements (~109.5°). This structure causes the molecule to have a net dipole moment. The C=O bond is significantly polar because oxygen is much more electronegative than carbon. The resulting molecular dipole points from the central carbon toward the oxygen atom.
Acetone is polar, allowing it to participate in dipole–dipole interactions, especially important in solubility and boiling point characteristics. Additionally, it exhibits London dispersion forces like all molecules. However, it cannot hydrogen bond with itself since it lacks an H directly bonded to O or N. This understanding of bonding, shape, polarity, and intermolecular forces is critical for predicting acetone’s physical properties and reactivity in organic chemistry.