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QuestionChemistry

What is the best resonance structure for SCN − , according to computer models and bond lengths? A. S-C double bond and C-N double bond. B. S-C single bond and C-N triple bond. C. S-C triple bond and C-N single bond. D. S-C single bond and C-N double bond.
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Answer

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Step 1:
Let's solve this step by step using structural analysis and bonding principles:

Step 2:
: Analyze the Lewis Structure

- SCN⁻ has a total of 16 valence electrons (S: 6, C: 4, N: 5, and 1 extra electron from negative charge) - We need to distribute these electrons to minimize formal charges and maximize electron delocalization

Step 3:
: Evaluate Resonance Structures

The SCN⁻ ion has three primary resonance structures: - S-C double bond, C-N single bond - S-C single bond, C-N double bond - S-C single bond, C-N triple bond

Step 4:
: Experimental Evidence

- Experimental bond length measurements and computational models show that the actual structure is a hybrid - The C-N bond has significant double bond character - The S-C bond is closer to a single bond

Step 5:
: Computational Analysis

- Quantum mechanical calculations indicate electron delocalization - The most stable structure shows partial double bond character between C and N - Experimental bond lengths support a structure with significant electron sharing

Step 6:
: Formal Charge Analysis

- The structure with S-C single bond and C-N double bond minimizes formal charges - This structure provides the most stable electron distribution

Final Answer

S-C single bond and C-N double bond. The resonance structure with a single S-C bond and double C-N bond best represents the electronic structure of SCN⁻ according to computational models and experimental bond length measurements.