Question

3. The dicationic and dianionic derivatives of cyclooctatetraene have been confirmed to be planar molecules. The neutral species, however, adopts a "tub-like" non-planar shape shown below. Calculate the n for all three species, where: n electrons = 4n + 2, and explain why this change in shape occurs in the neutral compound. H HH Cyclooctatetraene

Answer 1

for dicationic species – Number of op en is equal to 6 4n+ 2 s6 4n = 6-2 49:34, 'n 4 :1 According to Huckel rule. n: 1 for 4n+ 2 rule. (Aromatic) I for diangonic species in Number of op eis equal to 10. 4 n + 2 =10 4n 10-2 4n = 8 n: :2 According to Huckel rule, n = 2 for 4n+ 2 rule. ( Aromatic) Il for nental species Number of of e- is equal to 8. 40+2 = 8 4n = 8-2 4ns 6 n. 63 ī follow huckel Do not follow Huckel rule for aromatic but rule for antigromatic where n=2 4n -8 n : 8/4:22

If in neutral compound if the compound is planar than all pi bond will get into cyclic conjugation , then the compound will become anti aromatic which is highly unstable. So, compound remove it's planarity by twisting and convert into non aromatic compound . Non aromatic Compound is more stable than anti aromatic.