Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
Which of the following represent valid pairs of resonance structures? (i) (ii) (iii) (iv) (v)
Options
- A(i) and (iv)
- B(i), (ii), and (iii)
- C(ii), (iv), and (v)
- D(i), (iii), and (iv)
Correct answer
A. (i) and (iv)
Step-by-step solution
For two structures to be valid resonance structures, the relative positions of all atoms must remain the same. Only the distribution of pi electrons and non-bonding electrons can differ. Additionally, second-period elements (like C, N, O) cannot have more than 8 valence electrons. In pair (i), the structures are H₃C- O -CH=CH₂ and H₃C- + O =CH- C H₂⁻ . The nuclei are in identical positions. The lone pair on oxygen delocalizes to form a C=O double bond, and the C=C pi electrons shift to the terminal carbon. All atom