We have studied aromaticity in detail and are acquainted with various compounds that are aromatic. A variety of physical properties have been used as a
Author: Gauri Nigudkar
130.Aromaticity(23) – What is so special about 4n+2 π electrons?
We have been reiterating that aromatic compounds have 4n+2π electrons and antiaromatic compounds 4n π electrons. Ever wondered why these numbers are so important? Let’s
129.Aromaticity(22) -Antiaromaticity.
We saw earlier that aromaticity refers to the extra stability that some cyclic compounds have, owing to their structure. Antiaromaticity means exactly the opposite of
128.Aromaticity(21)- Fullerenes.
Elemental carbon in its sp2 hybridized state can form some very interesting structures, which have very wide applications in industry. Fullerenes are one such class
127.Aromaticity(20)-Annulenes (2).
Is [12]annulene aromatic? [12]annulene has 4n π electrons and so is anti-aromatic. It is highly unstable compound and exists only at very low temperatures. At
126.Aromaticity(19)- Annulenes(1).
Annulenes are completed conjugated monocyclic non-benzenoid hydrocarbons, with a general formula – CnHn ,when n is an even number CnHn+1 , when n is an
125.Aromaticity(18)- Polycyclic aromatic hydrocarbons(2)- Azulene,Anthracene, Phenanthrene, Pyrene, Phenacenes.
In the last post we studied naphthalene molecule in detail and we understood why it shows aromatic stability. Similarly , other polycyclic hydrocarbons are also
124.Aromaticity(17)- Polycyclic aromatic hydrocarbons(1)- Naphthalene.
In this post we shall discuss aromaticity of some polycyclic aromatic hydrocarbons (PAHs). What are polycyclic aromatic hydrocarbons? Poly = many cyclic = ring structure.
123.Aromaticity(16) – Heterocyclic aromatic systems(2)-Furan,pyrrole and thiophene.
Furan, Pyrrole and Thiophene. All the above structures are similar to each other , except for the fact that pyrrole has a lone pair and
122.Aromaticity(15) – Heterocyclic aromatic systems(1)-Pyridine.
In the last post we studied some examples of homocyclic aromatic compounds. What happens if the ring has an atom other than carbon in it?
121.Aromaticity(14) – Homocyclic charged aromatic systems.
Benzene with six π electrons – the aromatic sextet– is a “perfect” example of an aromatic compound. In this post we shall study some examples
120 . Aromaticity(13)- Cyclobutadiene and benzene.
We learned in detail how HMO theory explains the structure and aromaticity of benzene in previous posts. In this post let us compare benzene to
119.Aromaticity(12) – Frost Musulin diagram.
Frost circles/Polygon method. This is a very useful mnemonic device for quickly setting down molecular diagrams for cyclic systems. Rules for drawing frost circles –
118.Aromaticity(11) – HMO treatment to benzene(2).
In the last post we saw how the HMO theory explains the aromaticity of benzene ring. In this post let us see how we get
117.Aromaticity (10)- HMO treatment to benzene(1).
In this post let us apply the HMO theory to see how and why benzene is aromatic i.e why does this molecule have that extra
116.Aromaticity(9)- Calculations of HMO theory(3).
In the last post we computed Hückel calculations for two p orbitals in conjugation. Let us now try to figure out how to calculate energies for
115.Aromaticity(8) -Calculations of HMO theory(2).
In the previous post we arrived at two simultaneous equations (We are using two different colors in order to distinguish between the two equations)- ciα
114.Aromaticity(7) -Calculations of HMO theory(1).
In this post let us apply the LCAO method and approximations we studied earlier to a simple conjugated molecule and carry out the calculations for
113 – Aromaticity(6) – Hückel approximations.
The HMO theory makes certain approximations.These approximations have proved to be very useful as they help simplify calculations and give accurate results. So, they are
112.Aromaticity (5) – LCAO approach to HMO theory.
In the last post we got an overview of what matrices are and how they are used. Let us proceed further and see how this
111.Aromaticity (4) – Matrix
Before proceeding further, it is imperative that we understand some basic mathematical concepts required to study this theory. We are not going to elaborately study
110.Aromaticity(3)- Hückel Molecular theory (HMO).
Hückel’s molecular orbital(HMO) theory. The π- electron system in conjugated planar molecules can be treated independently of the σ framework. Aromaticity is usually described in
109.Aromaticity(2) -Hückel’s rule.
In the last post we introduced ourselves to a new concept in organic chemistry – Aromaticity. We will continue to discuss it in this post.
108.Aromaticity(1) – Introduction.
From this post onwards we begin discussing a new topic in organic chemistry.This topic deals with a certain class of organic compounds , which are
107.The structure of Benzene(2).
We studied the structure of benzene in the last post. However, the structure of benzene has many resonance contributors. The resonance structures of benzene
106. The structure of Benzene(1).
This topic is sort of a link between the earlier topic we discussed(Resonance) and the upcoming topic we shall start discussing soon. The structure of
105.Resonance(2)
In the last post we studied what resonance means and how resonating structures blend to give the resonance hybrid structure. In this post we shall
104.Resonance(1)
From this post onwards, we shall start discussing a phenomenon, which manifests itself in many compounds and which is responsible for deviations in structure, properties
103.CHEMICAL BONDING (50)- Practice Problems.
Q: Why is o- hydroxy benzaldehyde a liquid whereas p-hydroxy benzaldehyde a solid , with high MP, at room temperature ? A: o- hydroxy benzaldehyde
102.CHEMICAL BONDING (49)- Secondary bonding(6)- Hydrogen Bonding (4)
We continue to study the physical manifestations of H- bonds and their importance. Protein folding Hydrogen bonds are an integral part of the protein structure.
