For each of the following compounds, draw the important resonance forms. Indicate which structures are major and minor contributors or whether they have the same energy.
(c) [H₂COCH₃]⁺

Verified step by step guidance

1. Identify the structure of the compound [H2COCH3]+. This is a protonated acetaldehyde, where the positive charge is on the oxygen atom.
2. Draw the Lewis structure of the compound, showing all atoms, bonds, and the positive charge on the oxygen atom.
3. Consider the movement of electrons to form resonance structures. The positive charge on the oxygen can be delocalized by moving the lone pair of electrons from the oxygen to form a double bond with the adjacent carbon atom.
4. Draw the resonance structure where the oxygen forms a double bond with the carbon, and the positive charge is now on the carbon atom. This is a major contributor because it allows the positive charge to be on a less electronegative atom (carbon) compared to oxygen.
5. Evaluate the resonance structures: The structure with the positive charge on the carbon is a major contributor due to the stability provided by the delocalization of charge. The original structure with the positive charge on the oxygen is a minor contributor because the charge is on a more electronegative atom, which is less stable.

Key Concepts

Resonance Structures

Resonance structures are different Lewis structures for a molecule that depict the same arrangement of atoms but differ in the distribution of electrons. They are used to represent delocalized electrons within certain molecules where the bonding cannot be expressed by a single Lewis structure. Understanding resonance is crucial for predicting the stability and reactivity of molecules.

Major and Minor Contributors

In resonance, not all structures contribute equally to the resonance hybrid. Major contributors are the most stable structures, typically having the least charge separation and full octets on atoms. Minor contributors are less stable, often with more charge separation or incomplete octets. Identifying these helps in understanding the true electron distribution in the molecule.

Formal Charge

Formal charge is a bookkeeping tool used to determine the charge distribution within a molecule. It is calculated by assuming equal sharing of electrons in bonds. Structures with formal charges closest to zero are generally more stable. Calculating formal charges helps in identifying major and minor resonance contributors by highlighting the most stable electron arrangements.