Question

Given below are the $\Delta E$ for some isodesmic reactions. Also given are the AIM and NPA charges at the carbon atoms of the double bond. Provide an explanation for these results in terms of both resonance structure and MO terminology. a. Draw resonance structures and qualitative MO diagrams that indicate the stabilizing interaction. b. Explain the order of stabilization $\mathrm{N}>\mathrm{O}>\mathrm{F}$ in both resonance and $\mathrm{MO}$ terminology. c. Interpret the AIM and NPA charges in relationship to the ideas presented in (a) and (b). $$ \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{X}+\mathrm{CH}_{2}=\mathrm{CH}_{2} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}+\mathrm{CH}_{2}=\mathrm{CHX} $$ \begin{tabular}{llllll} \hline $\mathrm{X}$ & $\Delta E$ & $\delta \mathrm{C}(1)^{a}$ & $\delta \mathrm{C}(2)^{a}$ & $\delta \mathrm{C}(1)^{b}$ & $\delta \mathrm{C}(2)^{b}$ \\ \hline $\mathrm{H}$ & 0 & $+0.08$ & $+0.08$ & $-0.25$ & $-0.25$ \\ $\mathrm{CH}_{3}$ & $-3.05$ & $+0.02$ & $+0.08$ & $-0.09$ & $-0.29$ \\ $\mathrm{NH}_{2}$ & $-7.20$ & $+0.51$ & $+0.15$ & $+0.14$ & $-0.36$ \\ $\mathrm{OH}$ & $-6.43$ & $+0.58$ & $+0.18$ & $+0.26$ & $-0.39$ \\ $\mathrm{~F}$ & $-0.99$ & $+0.48$ & $+0.29$ & $+0.30$ & $-0.36$ \\ \hline \end{tabular} a. AIM charges b. NPA charges 

   Given below are the $\Delta E$ for some isodesmic reactions. Also given are the AIM and NPA charges at the carbon atoms of the double bond. Provide an explanation for these results in terms of both resonance structure and MO terminology.
a. Draw resonance structures and qualitative MO diagrams that indicate the stabilizing interaction.
b. Explain the order of stabilization $\mathrm{N}>\mathrm{O}>\mathrm{F}$ in both resonance and $\mathrm{MO}$ terminology.
c. Interpret the AIM and NPA charges in relationship to the ideas presented in (a) and (b).
$$
\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{X}+\mathrm{CH}_{2}=\mathrm{CH}_{2} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}+\mathrm{CH}_{2}=\mathrm{CHX}
$$
\begin{tabular}{llllll}
\hline $\mathrm{X}$ & $\Delta E$ & $\delta \mathrm{C}(1)^{a}$ & $\delta \mathrm{C}(2)^{a}$ & $\delta \mathrm{C}(1)^{b}$ & $\delta \mathrm{C}(2)^{b}$ \\
\hline $\mathrm{H}$ & 0 & $+0.08$ & $+0.08$ & $-0.25$ & $-0.25$ \\
$\mathrm{CH}_{3}$ & $-3.05$ & $+0.02$ & $+0.08$ & $-0.09$ & $-0.29$ \\
$\mathrm{NH}_{2}$ & $-7.20$ & $+0.51$ & $+0.15$ & $+0.14$ & $-0.36$ \\
$\mathrm{OH}$ & $-6.43$ & $+0.58$ & $+0.18$ & $+0.26$ & $-0.39$ \\
$\mathrm{~F}$ & $-0.99$ & $+0.48$ & $+0.29$ & $+0.30$ & $-0.36$ \\
\hline
\end{tabular}
a. AIM charges
b. NPA charges
Show more…
Advanced Organic Chemistry. Part A. Structure and Mechanisms
Advanced Organic Chemistry. Part A. Structure and Mechanisms
Francis A. Carey,… 5th Edition
Chapter 1, Problem 13 ↓
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Given below are the $\Delta E$ for some isodesmic reactions. Also given are the AIM and NPA charges at the carbon atoms of the double bond. Provide an explanation for these results in terms of both resonance structure and MO terminology. a. Draw resonance structures and qualitative MO diagrams that indicate the stabilizing interaction. b. Explain the order of stabilization $\mathrm{N}>\mathrm{O}>\mathrm{F}$ in both resonance and $\mathrm{MO}$ terminology. c. Interpret the AIM and NPA charges in relationship to the ideas presented in (a) and (b). $$ \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{X}+\mathrm{CH}_{2}=\mathrm{CH}_{2} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{3}+\mathrm{CH}_{2}=\mathrm{CHX} $$ \begin{tabular}{llllll} \hline $\mathrm{X}$ & $\Delta E$ & $\delta \mathrm{C}(1)^{a}$ & $\delta \mathrm{C}(2)^{a}$ & $\delta \mathrm{C}(1)^{b}$ & $\delta \mathrm{C}(2)^{b}$ \\ \hline $\mathrm{H}$ & 0 & $+0.08$ & $+0.08$ & $-0.25$ & $-0.25$ \\ $\mathrm{CH}_{3}$ & $-3.05$ & $+0.02$ & $+0.08$ & $-0.09$ & $-0.29$ \\ $\mathrm{NH}_{2}$ & $-7.20$ & $+0.51$ & $+0.15$ & $+0.14$ & $-0.36$ \\ $\mathrm{OH}$ & $-6.43$ & $+0.58$ & $+0.18$ & $+0.26$ & $-0.39$ \\ $\mathrm{~F}$ & $-0.99$ & $+0.48$ & $+0.29$ & $+0.30$ & $-0.36$ \\ \hline \end{tabular} a. AIM charges b. NPA charges
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Key Concepts

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Charge Analysis Methods (AIM and NPA)
Charge analysis methods such as Atoms in Molecules (AIM) and Natural Population Analysis (NPA) offer insights into the distribution of electron density in molecular frameworks. These analyses help relate the observed charge distribution on atoms (especially in ? systems) to the extent of electron donation or withdrawal via resonance and MO interactions, thereby supporting the interpretation of stabilization trends across different substituents.
Isodesmic Reaction Energetics
Isodesmic reactions are used to compare the relative stabilities of molecules by keeping the number and types of chemical bonds constant. The small differences in reaction energies (?E) provide quantitative measures of stabilization effects imparted by different substituents. This approach helps correlate the theoretical predictions from resonance/MO considerations with experimental or calculated energetic data.
Resonance Stabilization
This concept refers to the ability of a molecule to distribute electron density via alternative Lewis structures (resonance forms). In the context of the double bond adjacent to a heteroatom substituent, resonance stabilization is achieved when lone pair electrons on the substituent delocalize into the ? system. This delocalization reduces localized charge buildup and increases overall stability, with the effectiveness of delocalization being influenced by the nature of the substituent.
Molecular Orbital Theory
Molecular orbital (MO) theory describes bonding in terms of the combination of atomic orbitals to form molecular orbitals that extend over the entire molecule. For systems with a double bond and adjacent heteroatom, qualitative MO diagrams help illustrate how donor (nonbonding) orbitals on the substituent can interact with the ?* antibonding orbital of the double bond. This interaction leads to orbital mixing, energy splitting, and additional stabilization through delocalization.
Substituent Effects and Electronegativity
Different substituents (e.g., those containing nitrogen, oxygen, or fluorine) have varying abilities to stabilize a double bond via resonance or MO interactions due to differences in electronegativity, lone pair availability, and orbital overlap. Less electronegative atoms like nitrogen more readily donate electron density, resulting in greater stabilization, while more electronegative atoms like fluorine are less effective, thus establishing an order of stabilization that is reflected in both resonance and MO descriptions.
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Inorganic Chemistry for Jee mains and Advanced

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Transcript

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00:01 The question is the correct stability order of the following resonance structures.
00:03 So we are going to discuss what is the correct order of the resonance structures.
00:09 First is the ch2 double bond, n plus, double bond and triple bond n minus.
00:14 Ch2 plus and triple bond n minus.
00:19 Ch2 minus n plus triple bond n ch2 minus and triple bond n plus...
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