aromatic,Anti-aromatic and non-aromartic compounds

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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) =2 π 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 4 π 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 cyclic \acyclic Planar planar planar \ nonplanar Conjugated conjugated conjugated \non Every atom every atom sp2 at least one atom is Sp2 hybridized hybridized sp3 hybridized (4n+2) π e- (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 2 π e- (follow huckel’s rule) stable Result : cyclopropenyl cation is Aromatic

9. CYCLOBUTADIENE Cyclic Planar Conjugated Each carbon atom is sp2 4 π 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 6 π 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 6 π 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 6 π e- Result: 1,3,5-cycloheptatriene is non aromatic

18. 1,3,5-cycloheptatrienyl cation Cyclic Planar Conjugated Each C atom is sp2 hybridized 6 π 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 becomes H H RESULT: cyclodecapentaene is non-aromatic

21. cyclopropanone Cyclic Planar 3 π 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