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In the conversion of N2⁻ to N2⁺, which of the following statements about the electrons removed is correct?

1. The 1st electron is removed from a gerade bonding MO
2. The 2nd electron is removed from an ungerade bonding MO
3. The 1st electron is removed from a gerade antibonding MO
4. The 2nd electron is removed from a gerade non-bonding MO

Correct answer: The 1st electron is removed from a gerade bonding MO

Solution

MO configuration of N2: (sigma₁s)² (sigma*₁s)² (sigma₂s)² (sigma*₂s)² (pi₂p)⁴ (sigma₂p)². N2 has 14 electrons. N2⁻ has 15 electrons: extra electron goes into pi*₂p (ungerade, antibonding). N2⁺ has 13 electrons (removed from pi₂p, ungerade bonding). To go from N2⁻ (15e) to N2⁺ (13e), two electrons are removed: 1st from pi*₂p (ungerade antibonding, HOMO of N2⁻), 2nd from pi₂p (ungerade bonding). The 1st electron removed is from pi*₂p — which is ungerade (u) and antibonding. The 2nd electron removed is from pi₂p — which is ungerade (u) and bonding. Option (B): '2nd electron removed from ungerade bonding MO' = correct description. But option (A) says '1st from gerade BMO' — pi*₂p is ungerade not gerade. Option (B): 2nd from ungerade BMO — pi₂p is indeed ungerade bonding. Option (B) is correct.

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