organic chemistry aromaticity

1. -BY KHAN RAHEELA
MSc PART-I

2. TOPIC INCLUDES :
AROMATIC COMPOUNDS [BENZENOID
COMPOUNDS ,ETC] .
ANTI AROMATIC COMPOUNDS .
ANNULENES .
HETEROCYCLIC COMPOUNDS .
METALLOCENES .

3. WHAT IS AROMATICITY
AROMATICITY IS A PROPERTY OF CONJUGATED CYCLOALKENES IN
WHICH THE STABILIZATION OF A MOLECULE IS ENHANCED DUE TO
THE ABILITY OF ELECTRON IN THE ‫ח‬ ORBITALS TO DELOCALIZE
.COMPOUNDS WHICH POSSES SUCH PROPERTY ARE AROMATIC
COMPOUNDS.

4. GENERAL REQUIREMENTS OF AROMATIC
COMPOUNDS:
i. THEY MUST BE CYCLIC , COMPLETELY
CONJUGATED .
ii. THEY MUST FOLLOW HUCKEL RULE OF (4n + 2)‫ח‬
ELECTRON SYSTEM .
iii.THEY MUST BE PLANAR . ALL ADJACENT P
ORBITALS MUST BE ALIGNED SO THAT ‫ח‬
ELECTRONS CAN BE DELOCALIZED .
iv.FOR EXAMPLE : BENZENE AND ITS DERIVATIVES .

7. WHY AROMATIC COMPOUNDS ARE MORE
PREFERABLE :
THEY ARE HIGHLY STABLE MOLECULES .
THEY UNDERGOES SUBSITUITION REACTION RATHER
THAN ADDITION REACTION .

8. BASICALLY AROMATIC COMPOUNS
INCLUDES NON-BENZENOID
COMPOUNDS , BENZENOID
COMPOUNDS ,
SOME ANNULENES ,
HETEROCYCLIC COMPOUNDS ,
METALLOCENES , FULLERENCES ,
ETC .

10. ANTIAROMATIC COMPOUNDS :
AS LIKE AROMATIC COMPOUNDS THERE ARE ALSO
SOME ANTIAROMATIC COMPOUNDS EXIST WHICH
POSSES CHARACTERISTICS AS FOLLOW :
THEY MUST BE CYCLIC , PLANAR , COMPLETELY
CONJUGATED .
THEY MUST FOLLOW HUCKEL RULE OF 4n‫ח‬
ELECTRONS .
FOR EXAMPLE :CYCLOBUTADIENE , PENTALENE ,
ETC .

12. AROMATICITY OF BENZENOID COMPOUNDS:
BENZENE AND ITS DERIVATIVES ARE AROMATIC
IN NATURE .
THEY HAVE SP2 HYBRIDIZED CARBON ATOMS AS
WELL AS DELOCALIZED PI ELECTRON CLOUD .
THEY ARE MORE STABLE COMPOUNDS .
KEKULE FIRST PROPOSED STRUCTURE OF
BENZENE IN 1865 .
SOME BENZENOIDS ARE NAPTHALENE ,
ANTRACENE , ETC .

14. ANNULENES :
ANNULENES ARE COMPOUND CONTAINING 7 OR
MORE CARBON ATOMS .
 ANNULENES ARE MONOCYCLIC COMPOUNDS
CONTAINING ALTERNATING RING DOUBLE BONDS .
THERE ARE 10 ANNULENE ,14 ANNULENES , 16
ANNULENE ,18 ANNULENES & SO ON.
SOME ARE AROMATIC , ANTI AROMATICS & NON
AROMATIC .

16. HETEROCYCLIC COMPOUNDS :
HETEROCYCLIC COMPOUNDS ARE CYCLIC COMPOUNDS
CONTAINING ONE ATOM OTHER THAN CARBON ATOM , IT
CAN BE NITROGEN , OXYGEN , SULPHUR , ETC.
THEY CAN BE EITHER AROMATIC OR ANTIAROMATIC OR
NONAROMATIC .
MOST COMMON EXAMPLES ARE FURAN , PYRROLE ,
THIOPENE , PYRIDINE .

17. PYRROLE
PYRIDINE
THIOPENE
FURAN

18. METALLOCENES :
Organometallic coordination compounds in which one atom of a
transition metal such as iron, ruthenium or osmium is bonded to and
only to the face of two cyclopentadienyl [[hap to]5-(C5H5)] ligands
which lie in parallel planes.
FOR EXAMPLE : FERROCENE .

20. REFERENCES :
https://www.britannica.com/science/benzenoid-
aromatic-compound .
http://www.chemvista.org/annulenes2.html.