A Short Note On The Geometry Of Carbanions

When carbon possesses an unshared pair of electrons, it can form an anion with a negative charge. 

A carbanion is typically composed of three substituents for a total of eight valence electrons.

Because of its trigonal pyramidal shape, the carbanion is a molecule. Carbon acids are the conjugate bases of other acids, while carbanion is the conjugate base of another acid.

      R3C−H+B−→R3C−+H−B

In this case, B denotes the foundation. Among the reactive intermediates in organic chemistry are carbanions, which is one of several.

Cleavage of heterolytic bonds results in the formation of carbocation ligands. Sp2 hybridization occurs in the case of CH+3. 

It is made up of one s-orbital and two p-orbitals in equal proportions. 

Carbocation possesses three sigma bonds, which results in a trigonal planar shape. H and C all lie on the same plane as each other.

Trigonal Planar Geometry Is Characterised By The Following Characteristic

It is made up of three sp2 hybrid orbitals that are evenly spaced and positioned at an angle of 120° degrees from one another.

A triangle planar shape is formed by the orbitals.

Due to the presence of one atom at the end of each orbital, the geometry of the molecule is also trigonal planar in nature.

π Delocalization

When the atomic orbitals of two bonding atoms cross in the same direction, pi bonds are created.

Unlike the plane of the molecule, the pi-electron cloud is perpendicular to it.

Pi bonds are weaker than sigma bonds because sideways overlap is less effective than the head to head overlap that occurs in a sigma bond.

In most organic compounds, one sigma bond is found in every bond between atoms, which is common. 

Sigma bonds are formed by combining single bonds.

2 sigma bonds + 2 pi bonds=l 1 double bond

For every sigma bond, there are two pi bonds added together to form a triple bond.

The electrons are said to be localised when they are in a specific place.

In penta-1,4-diene, the electrons are still confined to a small region of the compound.

In order to keep the two orbitals from overlapping, the CH2 group is formed between them.

While in buta-1,3-diene, the two orbitals can overlap, the electrons are free to spread out across all four carbon atoms, as opposed to in other organic compounds.

These electrons are referred to as delocalized in our terminology.

It is possible to delocalize all six carbon atoms in benzene, which is what happens in the ring structure of the compound.

Bent’s Rule

The relationship between the orbital hybridization of core atoms in molecules and the electro-negativities of substituents is described and explained by Bent’s Rule. 

As stated by Henry Bent, the rule is as follows “Atomic s character concentrates in orbitals pointed toward electropositive substituents. “

The substituent group can be used to describe and forecast things like molecular shape, for example.

Among the main group elements, C, Si, Ge, Sn, and Pb are represented by the letter X. 

The bond angle Cl-X-Cl in the molecule Me₂XCl₂ is less than that of the main group element C. 

Cl is a highly electronegative halogen substitution that concentrates more p character in its centre than the central atoms of the X-C bonds. 

This is due to the electronegative nature of the halogen substituent.

Given that the s- orbital is closer to the nucleus, it stands to reason that when the s-character of a hybrid orbital grows, the electronegativity of the hybrid orbital increases with it as well.

VSEPR Theory

A model used in chemistry to predict the geometry of particular molecules based on the amount of electron pairs surrounding their centre atoms is called the Valence Shell Electron Pair Repulsion (VSEPR) theory.

Gillespie-Nyholm theory is sometimes known as the Gillespie-Nyholm hypothesis after the two principal creators of the theory, Ronald Gillespie and Ronald Nyholm.

It is believed that the valence electron pairs around an atom have a natural tendency to resist one another and, as a result, will arrange themselves in a way that reduces this repulsion.

It is this drop in energy and increase in stability of the molecule that dictates the molecular shape of the compound. 

Electrostatic repulsion is significant in establishing molecular geometry, but the electron-electron repulsion caused by the Pauli exclusion principle is far more important, according to Gillespie.

A topological examination of the electron density of molecules provides the basis for the VSEPR theory’s conclusions.

The electron localization function (ELF) and the quantum theory of atoms in molecules are examples of quantum chemical topology (QCT) approaches. 

This means that valence-bond theory’s VSEPR has nothing to do with wave function-based approaches such as orbital hybridization.

It is possible to anticipate the arrangement of electron pairs around core atoms in molecules using the VSEPR theory, which is particularly useful for simple and symmetric compounds. 

This theory defines a central atom as an atom that has formed bonds with two or more other atoms. 

A terminal atom, on the other hand, has formed bonds with only one additional atom.

Examples of central atoms include the two carbons and one nitrogen in the molecule methyl isocyanate (H3C-N=C=O), and terminal atoms include the three hydrogens and one oxygen.

The geometry of the central atoms and their non-bonding electron pairs determines the geometry of the larger entire molecule, which in turn is determined by the geometry of the central atoms and their non-bonding electron pairs

Conclusion

Essentially, a carbocation is an organic molecule, or an intermediate, that forms as a result of the loss of two valence electrons, which are normally shared electrons, from a carbon atom that already has four bonds.

A carbocation is a compound that contains two carbon atoms joined together by four bonds.

A positive charge and three bonds are formed instead of four bonds in the creation of a carbon atom with this configuration.

Sp² hybridisation occurs in the carbocation’s core positively charged carbon atom. 

Because of their hybridisation, the three sp² orbitals establish three bonds with each of the three hydrogen atoms. This means that the unhybridized p-orbital is still available.

 So the carbocation is trigonal planar or flat in shape, as a result of which it is named.