Draw Lewis structures for the nine isomers having molecular formula C3H6O, with all atoms having a zero formal charge.
The correct answer and explanation is :
To draw the Lewis structures for the nine isomers with the molecular formula (C_3H_6O), we need to consider different arrangements of atoms and bonding that satisfy the molecular formula and the condition of having a zero formal charge on all atoms.
The general steps to drawing the Lewis structures are:
- Count the total valence electrons:
- Carbon (C) has 4 valence electrons, hydrogen (H) has 1, and oxygen (O) has 6.
- For (C_3H_6O), the total number of electrons is:
[
3 \times 4 + 6 \times 1 + 1 \times 6 = 12 + 6 + 6 = 24 \, \text{electrons}.
]
- Connect atoms with single bonds and distribute the remaining electrons to fill the octets (8 electrons) for atoms (except hydrogen, which only needs 2 electrons).
- Minimize formal charges by rearranging electrons as needed.
Now, let’s look at the possible isomers:
1. Propanol (CH3CH2OH)
- In this structure, the hydroxyl group (-OH) is attached to a propane chain. The oxygen forms a single bond with carbon, and the remaining electrons complete the octet for oxygen.
2. Acetone (CH3COCH3)
- Here, a carbonyl group (C=O) is bonded to two methyl groups (CH3). The oxygen atom in the carbonyl group has two lone pairs of electrons, and the carbon atoms form single bonds to hydrogen.
3. Ethenol (CH2=CH-OH)
- This structure features a vinyl group (CH2=CH) with a hydroxyl group (-OH) attached to one of the carbons.
4. Cyclopropanol (C3H6O)
- A three-membered carbon ring with an alcohol group (-OH) attached to one of the carbons.
5. Methanol (CH3OH)
- A single methyl group (CH3) bonded to a hydroxyl group (-OH).
6. Ethenone (CH2=COCH3)
- A carbonyl group (C=O) with a vinyl group (CH2=) attached to it.
7. Propenal (CH2=CH-CHO)
- This compound contains a vinyl group (CH2=CH) attached to an aldehyde group (-CHO).
8. Isopropanol (CH3CHOHCH3)
- A secondary alcohol (OH) attached to a central carbon atom, which is also bonded to two methyl groups (CH3).
9. Cyclopropanone (C3H6O)
- A three-membered ring with a carbonyl group (C=O) attached to one of the carbon atoms.
Formal Charges
- For all these structures, each atom should have zero formal charge. This is achieved by ensuring each atom has the correct number of electrons for its valence shell.
Explanation:
The nine isomers can be classified based on their bonding and functional groups:
- Alcohols: Propanol, Cyclopropanol, Methanol, and Isopropanol.
- Aldehydes: Propenal, and Acetone (due to the presence of a carbonyl group).
- Ketones: Acetone and Ethenone.
- Ethers and Vinyl Compounds: Ethenol, Cyclopropanone.
Each structure is stable with zero formal charge on all atoms, achieved by correctly assigning bonding pairs and lone pairs, ensuring the total number of valence electrons is satisfied.