Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	The compound tetraene has the following structural formula. It is a cyclic and has conjugated 8π electrons system but it is not an aromatic compound.
Reason (R):	( 4 n + 2 ) π electrons rule does not hold good for this compound and the ring is not planar.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: cyclooctatetraene is not a planar compound

According to Huckel rule Aromaticity is shown by compounds possessing the following characteristics

(i) Compound must be planar and cyclic

(ii) Complete delocalization of

π

electrons in the ring

(iii) Presence of conjugated

(4 n + 2) π

electrons in the ring where n is an integer (n=0,1,2,....)

cyclooctatetraene (given) has a tub-like structure. It loses planarity. The number of

{πe}^{-}

delocalized is 8 and n is not an

integer. Hence, cycloctatetraene is a non-aromatic compound.

Thus, both assertion and reason are true and the reason is the correct explanation of assertion.