The document outlines the criteria for classifying compounds as aromatic, anti-aromatic, or non-aromatic based on their structural properties and electron configurations. Aromatic compounds must meet specific conditions, including having a cyclic, planar structure and obeying Huckel's rule, while anti-aromatic compounds contain 4n π electrons and exhibit instability. Various examples of compounds are provided to illustrate these concepts, including benzene, cyclobutadiene, and napthalene.

1. BY:MARIA ARSHAD
YOUTUBE CHANNEL:CHEMISTRY PHILICS
LET’S MAKE CHEMISTRY EASY AND LOVEABLE BY HAVING STRONG
CCONCEPTS
How to decide
whether one is
Aromatic,
Anti-Aromatic
or
Non-Aromatic
Compound

2. AROMATIC COMPOUNDS
 DEFINITION:
 Any cyclic compound which chemically
resemble benzene by both experimental and
theoretical point of view is called aromatic
compound.
 Criteria of aromaticity:
 Cyclic and planner structure
 Each atom is sp2 hybridized
 Have unhybridized P- orbital for delocalization of
pi electrons
 Must be stable
 Must obey Huckel’s rule

3. Huckel’s rule
 All those cyclic ,planar,conjugated
compounds are aromatic which contain
(4n+2)π electrons.
 (4n+2)π eletrons where: n=0,1,2,3,4,5…
 n=0 (4(0)+2) =2π e-
 n=1 (4(1)+2) =6 π e-
 n=2 (4(2)+2) =10 π e-
 n=3 (4(3)+2) =14 π e-

4. FOR EXAMPLE:
 BENZENE:
 Cyclic
 Planar
 Conjugated
 Each atom sp2 hybridized
 6 π e-
 Stable
 Result:
benzene is aromatic…

5. ANTI-AROMATIC
 Definition:
 All cyclic, planar conjugated compounds
which contain 4n π e- in rings
 4n π e- where n=1,2,3,4…..
 4(1) 4 π e-
 4(2) 8 π e-
 4(3) 12 π e-
 4(4) 16 π e-

6. FOR-EXAMPLE:
 CYCLOBUTADIENE:
 Cyclic
 Planar
 Conjugated
 Each carbon atom sp2 hybridized
 4π e- system
 Result :
 Cyclobutadiene is anti-aromatic

7. Non-aromatic
 Which do not follow one or more of the above criteria
 DIFFERENCE
 AROMATIC ANTI-AROMATIC NON-AROMATIC
 Cyclic cyclic cyclicacyclic
 Planar planar planarnonplanar
 Conjugated conjugated conjugatednon
 Every atom every atom sp2 at least one atom is
Sp2 hybridized hybridized sp3 hybridized
 (4n+2)πe- (4n)π e- 3,5,7,9… e-
2,6,10,14… 4,8,12,16…
 Stable unstable regular

8. PRACTICE:
 CYCLOPROPENYL CATION
 Cyclic
 Planar
 Conjugated
 Each C-atom sp2 hybridized
 2π e- (follow huckel’s rule)
 stable
 Result :
 cyclopropenyl cation is Aromatic

9. CYCLOBUTADIENE
 Cyclic
 Planar
 Conjugated
 Each carbon atom is sp2
 4π e- system
 Unstable
 Result:
 cyclobutadiene is anti-aromatic

10. BENZENE:
 Cyclic
 Planar
 Conjugated
 Each atom sp2 hybridized
 6 π e-
 Stable
 Result:
benzene is aromatic…

11. CYCLOOCTATETRAENE:
 Cyclic
 Conjugated
 8 π e- system
 So it should be anti aromatic
 But it is non-planar so due its non-planarity it
is non- aromatic
 Result:
 Cyclooctatetraene is non-aromatic

12. PYRROLE:
 Cyclic
 Planar
 Conjugated
 6 π e- system
 4 Carbons sp2 hybridized but N is sp3 hybridized so non
aromatic
 BUT
 Cyclic
 Planar
 Conjugated
 6 π e-
 4 C atom=sp2 hybridized
 N atom=sp2 hybridized
 Result:
 Pyrrole is aromatic due to this structure

13. FURAN:
 Cyclic
 Planar
 Conjugated
 6 π e-
 4 C atom sp2 hybridized O is sp3 hybridized
 So it should be non-aromatic
 BUT
 Cyclic
 Planar
 Conjugated
 6 π e-
 4 C atom is sp2 hybridized O is sp2 hybridized
 result:
 furan is aromatic due to this structure

14. THIOPHENE:
 Cyclic
 Planar
 Conjugated
 6 π e-
 4 C atom sp2 S is sp3 hybridized
 So it should be non- aromatic
 BUT
 Cyclic
 Planar
 Conjugated
 6π e- system
 4 C atom sp2 hybridized S atom is Sp2 hybridized so
 Result:
 Thiophene is aromatic due to this structure

15. PYRIDINE:
 Cyclic
 Planar
 Conjugated
 Each atom is Sp2 hybridized 5 C=sp2,N=sp2
 6π e- system
 So
 Result
 Pyridine is aromatic

16. 1,3-CYCLOPENTADIENE
 Cyclic
 Planar
 Non-conjugated
 Result: 1,3- cyclopentadiene is non aromatic
 1,3-cyclopentadienyl anion
Result: 1,3 cyclopentadienyl anion is aromatic

17. 1,3,5-CYCLOHEPTATRIENE
 Cyclic
 Planar
 non- conjugated
 6 C sp2
 1 C sp3 hybridized
 6π e-
 Result:
 1,3,5-cycloheptatriene is non aromatic

18. 1,3,5-cycloheptatrienyl
cation
 Cyclic
 Planar
 Conjugated
 Each C atom is sp2 hybridized
 6π e- system
 Result:
 1,3,5-cycloheptatrienyl cation is aromatic

19. Napthalene
 Cyclic
 Planar
 Conjugated
 Every C-atom is Sp2
hybridized
 10 π e- system
 Stable
 Result:
Napthalene is aromatic

20. Cyclodecapentaene
 Cyclic
 Conjugated
 Every C-atom is
 Sp2 hybridized
 10 π e- system
 but
 Due to repulsion and non-bonding
interaction of electronic cloud of hydrogens
structure do not remain planar it becomesH H
 RESULT:
 cyclodecapentaene is non-aromatic

21. cyclopropanone
 Cyclic
 Planar
 3π e- (do not obey huckle)
 But in resonating structure
 Cyclic
 Planar
 Conjugated
 2 π e- (obey huckle rule)
 Result:
 cyclopropanone is aromatic due to this
resonating structure

22. Azolene:
 Cyclic
 Planar
 Conjugated
 10 π e- system (overall) but in bigger ring 7e-
 And in small 5e-
 So aromatic
 Cyclic planar
 Conjugated
 Overall 10e- but in big ring 6 e-(huckle)
 In small ring 6 e- huckle
 Result:
 So it is more stable structure

23. THANK YOU