Show how resonance can occur in the following organic ions: (a) acetate ion, \(\mathrm{CH}_{3} \mathrm{CO}_{2}{ }^{-}\); (b) enolate ion, \(\mathrm{CH}_{2} \mathrm{COCH}_{3}{ }^{-}\), which has one resonance structure with a \(\mathrm{C}=\mathrm{C}\) double bond and an \(-\mathrm{O}^{-}\)group on the central carbon atom; (c) allyl cation, \(\mathrm{CH}_{2} \mathrm{CHCH}_{2}^{+}\); (d) amidate ion, \(\mathrm{CH}_{3} \mathrm{CONH}^{-}\)(the \(\mathrm{O}\) and the \(\mathrm{N}\) atoms are both bonded to the second \(\mathrm{C}\) atom).

Conjugated systems are a series of alternating single and double bonds found in certain organic molecules. The presence of these alternating bonds allows for greater stability through resonance, a concept vital to understanding many reactions in organic chemistry. In conjugated systems, the p orbitals overlap, creating a delocalized electron cloud above and below the plane of the molecule. This delocalization can enhance the stability of a molecule because the electrons are not confined to one specific bond or atom; instead, they are shared over several adjacent atoms.

• Conjugation requires alternating single and double bonds.
• This systems provide stability by electron delocalization.
• Key examples of molecules with conjugated systems include benzene and butadiene.

Lewis structures are simplified representations of molecules that show how valence electrons are distributed among atoms. They are fundamental in predicting the behavior of molecules during chemical reactions. The dots in Lewis structures represent electrons, and lines represent bonds between atoms. In drawing Lewis structures, certain rules must be followed:

• Count the valence electrons of all atoms in the molecule.
• Use electrons to form bonds between atoms.
• Distribute remaining electrons to satisfy the octet rule, if possible.

Resonance in Lewis structures is indicated when there's more than one valid way to arrange the electrons, resulting in multiple possible structures for the same molecule. Understanding how to draw Lewis structures is crucial for visualizing resonance in organic ions, as seen in the exercise's given organic ions.

Delocalization of electrons refers to the spread of electrons across several atoms rather than being fixed between two atoms in a normal covalent bond. Delocalization occurs in molecules with conjugated systems and is a key factor in stabilizing ions and radicals through resonance. The delocalized electrons can move freely around the molecule, which lowers the overall energy of the system.

• Delocalization leads to the stabilization of the molecule.
• It's a key feature in molecules that show resonance.
• Electron delocalization increases electron cloud density over several atoms.

In the given exercise, recognizing delocalization is essential to understanding how the electrons in acetate ion, enolate ion, allyl cation, and amidate ion can move within the molecule, creating different resonance structures.

Resonance structures are different Lewis structures of a molecule or ion that describe the same arrangement of atoms but differ in the placement of electrons. These structures are not in a static state but are visual abstractions that represent a hybrid of all possible configurations. Resonance structures provide insight into the multiple ways electrons can be arranged in a molecule that contains a conjugated system.

• Multiple resonance structures can describe the same molecule.
• They symbolize a hybrid of the electron configurations.
• Resonance structures must have the same number of valence electrons.

When examining resonance structures as in the acetate ion or enolate ion, it's important to remember that the actual molecule is a weighted average of these structures, which contributes to its stability and reactivity. Resonance allows for a more accurate description of where electrons are likely to be found and facilitates predictions of molecular behavior.