What is the lowest energy alternative resonance structure for this compound:

CH3-CH-N<triple bond>N

There is a negative charge on CH and a positive charge on the central N

CH3-CH-N<Triple bond>N

[CH3-(+CH)-N-N]-

To determine the lowest energy alternative resonance structure for the compound CH3-CH-N≡N with a negative charge on CH and a positive charge on the central N, we need to consider the concept of resonance and the rules governing the stability of resonance structures.

Resonance occurs when electrons in a molecule can be delocalized or spread across multiple atoms through π-bonds or lone pairs. Resonance structures are alternative representations of a molecule that can be formed by moving electrons while keeping the overall connectivity of the atoms intact.

To find the lowest energy resonance structure, we need to follow these steps:

1. Identify the electron-rich and electron-deficient regions: In this compound, the negative charge on CH indicates an excess of electrons (electron-rich region), while the positive charge on the central N indicates a deficiency of electrons (electron-deficient region).

2. Consider the movement of electrons: To achieve an alternative resonance structure, we can move one or more pairs of electrons from the electron-rich region to the electron-deficient region. In this case, we can move the lone pair of electrons from the N atom to form a double bond between the N and the adjacent carbon.

3. Evaluate resonance stability: Stability of resonance structures depends on the distribution of charges and the presence of formal charges (charges that do not represent actual charges but serve to show electronegativity differences). Lower formal charges and evenly distributed charges tend to make the structure more stable.

Now, based on the above steps, the lowest energy alternative resonance structure for the given compound is as follows:

CH3-CH=N≡N

In this structure, the lone pair of electrons on the N atom has been used to form a double bond between the N and the adjacent carbon. Both nitrogen atoms are involved in a triple bond, and the formal charges are as follows:

-CH3: No formal charge
N (center): No formal charge
N (terminal): No formal charge

The lowest energy structure is achieved by minimizing formal charges and evenly distributing the charges throughout the molecule. The absence of formal charges in the resonance structure suggests greater stability compared to structures with formal charges.

Note: Without experimental evidence or further calculations, it is difficult to definitively determine the relative energy levels of resonance structures. However, following these guidelines usually helps identify the most stable resonance structure.