Classify the following compounds as aromatic, anti-aromatic or non-aromatic compounds: (a) Cyclopropenyl cation (b) Naphthalene (c) Furan Pyrrole (e) Pyridine (f) Cycloctatetraene (g) 1,3,5-Cycloheptatriene.

Classify the following compounds as aromatic, anti-aromatic or non-aro

1.	Classify the following compounds as aromatic, anti-aromatic or non-aromatic compounds: (a) Cyclopropenyl cation (b) Naphthalene (c) Furan Pyrrole (e) Pyridine (f) Cycloctatetraene (g) 1,3,5-Cycloheptatriene.
Answer» Solution :(a) is aromatic as the rin is planar `4n+2=2pi -" electrons "( n= 0)` `pi`electrons are delocalized. (b) It has planar structure with delocalized ` (4*2+2) or 10pi` electrons obeys Huckel.s rule. It is aromatic. (c) The O atom and each of the four C atoms are in `sp^(2)` hybridized STATE forming a flat pentagonal structure. One of two lone PAIRS of electrons of the O atom is in `sp^(2)` orbital which is in the PLANE of ring and does not contribute towards aromatic sextet and the other in p orbital. Four p orbitals of four C atoms each containing `pi` electron and the filled p orbital of O are parallel to each other and perpendicular to the plane of furan. Therefore, furan has 4p electrons from four C atoms and 2p electrons from the O atom, i.e. it has six delocalized `pi` electrons which isa Huckel number. Hence,it is an aromatic compound. It has also resonance stablilzation as shown below: (d) Huckel number of delocalized `pi-` electrons are present in a planar cyclic structure Hence, it is aromatic. Here, lone PAIR of H- atom is contributing to aromatic sextet. (e) Since there are 6 delocalized p-electrons in planar hexagonal structure of pyridine, it is aromatic. (f) Cyclootatetraene has 8 `pi-` electrons. It has a puckered ring structure and proper overlap of `pi-`electrons are not possible . Hence , it is not an aromatic compound. (g) It has `4xx1+2=6 pi-` electrons but they are not delocalized. Hence, it is non-aromatic.