Question

Draw a major resonance structure for the following enolate. Use curved arrows in both structures to show the delocalization of electron pairs. Include lone pairs of electrons, formal charges, and hydrogen atoms.

Draw a major resonance structure for the following enolate. Use curved arrows in both structures to show the delocalization of electron pairs. Include lone pairs of electrons, formal charges, and hydrogen atoms.

Answer 1

Concepts and reason

The structure of a compound is given and resonance structure needs to be drawn showing curved arrows along with calculation of formal charge. Move the arrows in such a way that they are directed towards the most electronegative atom to get the major resonance structure.

Fundamentals

Resonance: The representation of some molecules can be done through several Lewis structures. These different structures of the same molecule are known as contributing structures. A hybrid of the contributing structures represents the real structure of the molecule and is known as resonance hybrid.

Such molecules having different Lewis structures exhibit resonance. Resonance occurs through the delocalization of lone pairs over various atoms within the molecule. Consider the example of nitrite ion:

Features of resonance:

• Each contributing structure showing resonance has the same bonding and non-bonding electrons.

• Resonance involves the movement of electrons and not the atoms.

• A double headed arrow is used to represent different contributing structures.

• The contributing structures having negative charge on more electronegative atom is more stable.

• The contributing structures that have opposite formal charges on adjacent atoms are more stable.

Formal charge: It is the charge possessed by an atom in a molecule.

The major resonance structure of the given structure is as follows:

The formal charges are as follows:

Resonance structure I: In the first resonating structure, ${{\rm{C}}_3}$ has formal charge of -1, ${{\rm{C}}_1}{\rm{,}}\;{{\rm{C}}_2}$ , O, and H has no charge.

Resonance structure II: In the second resonating structure, O has formal charge of -1, ${{\rm{C}}_1}{\rm{,}}\;{{\rm{C}}_2},\;{{\rm{C}}_3}$ , and H has no charge.

Ans:

The major resonance structure of the given structure is as follows:

Answer 2