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Thursday, January 31, 2019

Structure of “Borazine/Borazole”/inorganic Benzene:

(1) Borazine is an inorganic compound with the chemical formula  (B3N3H6).and also called Borazole. It is a heterocyclic compound, containing the 3-(BH) units and 3-(NH) units alternate.

(2) Borazine formed by reaction of B2H6 and NH3 in the ratio of 1:2 at room temperature.

(3) Borazine is isoelectronic and isostructural with benzene. For this reason borazine is known as “inorganic benzene”. Like benzene borazine has delocalized electrons and aromatic character. And it is a colourless liquid.

(4) In Borazine molecule nitrogen is more electro negative than the boron. Nitrogen acquires partial negative charge and boron acquires partial positive charge and back bonding take place between boron and nitrogen.

(5) As compared with Benzene, Borazole/borazine is less stable and more reactive toward Electrophilic Aromatic Substitution reactions due to presence of polar B-N bond in it while in benzene all the C-C bonds are non polar.

(6) Borazine is a highly polar molecule due to high Electronegativity difference between Boron and Nitrogen.

Even though Borazine/Borazole  and Benzene have same stricture their chemical properties are different.

(1) Organic benzene is C6H6 while Inorganic benzene is Borazine having chemical formula B3N3H6

(2) The pi bonds in borazine are highly polarized than pi bonds in benzene due to high polarity (B-N polar bond) of Borazine molecules. Thus borazine is more nucleophillic (Negative) hence more reactive than benzene with respect to “Electrophic addition reactions”.

Here protonation(H+) take place at nitrogen atoms due to more electron density (more negative)  and  chlorine attack at boron atoms.

(3) Aromaticity of borazine is less than benzene because some delocalization in Borazine/Borazole is not complete as benzene. One reason is that nitrogen atom has more electronegativity than boron ,the electron density is higher at nitrogen atoms then boron. The electron density is determined by both sigma and pi bonds, both of which have polarity, but opposite directions,   hence it is less reactive  toward “Electrophilic  substitution reactions” than Benzene. 

(4) Borazine undergo polymerization when strongly heated under vacuum and yield biborazonyl and naphthazine whose structure are similar to biphenyl and naphthalene.

Structure of "Borazon" (Cubic boron nitride):