Draw two bona fide Lewis resonance structures for methyl azide (
) showing all bonds & lone pairs and any formal charges (you can use partial structure below, which shows the bonding sequence, for the 1st one):

  1. Draw a second resonance structure for the reactive intermediate shown below: Show all valence electrons as bonds or lone pairs & indicate any formal charges.

The Correct Answer and Explanation is:

To draw two bona fide Lewis resonance structures for methyl azide (CH₃-N₃), let’s first understand the bonding sequence and the general structure.

Structure of Methyl Azide (CH₃-N₃):

Methyl azide consists of a methyl group (CH₃-) attached to a nitrogen group (N₃). The N₃ part has a linear arrangement, with a central nitrogen atom bonded to two other nitrogen atoms (one on each side).

The bonding sequence is:

  • The central nitrogen atom in N₃ (the N attached to CH₃) is connected to the other two nitrogens.
  • The central nitrogen atom will have lone pairs, while the nitrogens at the ends can have formal charges.

First Resonance Structure:

  1. CH₃-N≡N⁻–N⁺:
    • The CH₃ group (methyl) is single-bonded to the central nitrogen (N).
    • The nitrogen attached to the CH₃ group (N) has a triple bond to the adjacent nitrogen atom (N).
    • The terminal nitrogen (on the far right) has a positive charge, and the adjacent nitrogen (on the left) has a negative charge.
    In this structure:
    • The central nitrogen has a lone pair.
    • The terminal nitrogen on the right side has a positive formal charge (+1).
    • The nitrogen on the left side has a negative formal charge (-1).

Second Resonance Structure:

  1. CH₃-N⁺-N≡N⁻:
    • In this structure, the formal charges are swapped between the terminal nitrogens.
    • The nitrogen attached to the CH₃ group (N) has a positive formal charge.
    • The nitrogen on the far right is triple-bonded to the central nitrogen, while the nitrogen on the left has a negative charge.
    In this structure:
    • The central nitrogen (attached to CH₃) has a positive charge.
    • The nitrogen on the far left (N) has a negative formal charge.

Explanation of Resonance:

  • Both resonance structures depict the same bonding arrangement, but the formal charges are redistributed. The two nitrogens at the ends of the N₃ group can each hold a formal charge in different configurations, contributing to the overall resonance hybrid.
  • The total number of electrons and bonds remain the same in both structures.
  • The formal charges are significant because they determine the reactivity of the molecule in different environments.

Conclusion:

These two structures are both valid representations of methyl azide, and the actual structure is a hybrid of both. The resonance structures help us understand how the molecule might behave, especially in reactions where electron distribution is important.

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