Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
Consider the given canonical structures of pyridine: Which of the following represents the correct order of their stability?
Options
- A(iii) > (ii) = (iv) > (i) = (v)
- B(i) = (v) > (iii) > (ii) = (iv)
- C(i) = (v) > (ii) = (iv) > (iii)
- D(ii) = (iv) > (i) = (v) > (iii)
Correct answer
C. (i) = (v) > (ii) = (iv) > (iii)
Step-by-step solution
The stability of resonance structures is determined by a set of standard rules: First, neutral structures (without formal charge separation) are more stable than dipolar or charged structures. Structures (i) and (v) are neutral Kekule structures, so they are the most stable. Since they are equivalent, (i) = (v) . Second, among dipolar structures, those with opposite charges closer together are more stable due to stronger electrostatic attraction (lesser charge separation). In structures (ii) and (iv) , the positive