Aromaticity in benzenoid and non-benzenoid compunds

Semester 1 Manisha

1. Samrat Prithviraj Chauhan Government College , Ajmer Department of Chemistry Aromaticity in Benzoid and non-benzoid compounds Submitted by : Manisha M.Sc.[ Chemistry] Sem -I

2. CONTENT INTRODUCTION AROMATICITY RULES OF AROMATICITY AROMATICITY IN BENZENOID COMPOUNDS AROMATICITY IN NON-BENZEOID COMPOUNDS REFERENCE

3. INTRODUCTION Aromaticity is one of the crucial concepts in organic chemistry because most of the organic compounds we come across are aromatic. Organic compounds exhibiting delocalization of pi electrons are aromatic and are referred to as aromatic compounds. On the other hand, organic compounds which do not exhibit delocalization of pi electrons are referred to as non-aromatic or aliphatic compounds. Compared to aliphatic compounds, aromatic compounds exhibit more excellent stability.

4. AROMATICITY Aromaticity is defined as a property of the conjugated cycloalkenes which enhances the stability of a molecule due to the delocalization of electrons present in the π-π orbitals. Aromatic molecules are said to be very stable, and they do not break so easily and also reacts with other types of substances. The organic compounds which are not said to be aromatic are known as aliphatic compounds. These might be in cyclic form, but only the aromatic rings have a special kind of stability.

5. RULES OF AROMATICITY The aromatics compounds are said to exhibit some special characteristics or called as rules which are given below- The aromatic compounds are always cyclic structures. Each element of the ring within the structure must and should have a p-orbital ring which is in a perpendicular form to the ring, and this makes it a planar molecule The total number of π–electrons present in the ring should be equal to (4n + 2), where n= 0, 1, 2 … etc. This is known as Hackle's rule.

6. . The molecule must be planar or flat. Those compounds that follow the above rules of Aromaticity are generally flat as in that condition they possess extremely large potential energy.

7. AROMATICITY IN BENZENOID COMPOUND Benzenoid aromatic compounds are the organic molecular species either with isolated benzene ring or with multiple benzene rings which fused to form amore complex structure. Aromatic molecules are very stable ,and generally undergo electophilic substitutions rather than addition . Since the most common aromatic compound are derevatives of benzene.

8. . For resonance diagrams the use of double headed arrow indicates that two structures are not distinct entities but merely hypothatical possibalities. These compounds further be classified into monocyclic aromatic compounds and polycyclic aromatic compounds. MONOCYCLIC AROMATIC COMPOUNDS

9. P0LYCYCLIC AROMATIC COMPOUNDS naphthalene 111,1’-biphenyl anthracene

10. Aromaticity in non-benzenoid compounds Non-benzenoid compounds are the organic molecular species either with all carbons in the cycle or with one or more hetro atoms in the rings. A compound which exibhitics an aromatic behaviour but does not contain any benzene nucleus. The non-bezenoid aromatic compound have one or more rings fused but non of these rings is benzene ring . The ring might contain 7,5 etc. number of carbons but that ring will not be benzene ring. The most basic example of non-benzenoid aromatic compounds is AZULENE . It is a system of two fused rings, one containing 7 and the other containing 5 carbons.

11. . Fig .- Azulene These compounds can further be classified into homocyclic (carbocyclic) aromatic compounds and heterocyclic aromatic compounds.

12. HOMOCYCLIC AROMATIC COMPOUNDS TROPONE TROPOLONE

13. HETEROCYCLIC AROMATIC COMPOUNDS

14. REFERENCE https://www.masterorganicchemistry.com https://mltcollege.org https://www.britannica.com https://chem.libretexts.org https://courses.lumenlearning.com

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