Odd Electron Bond

Odd Electron Bond

It may be defined as, “The bonds in which odd numbers of electrons are used in its formation are known as odd-electron bonds and the molecules are called odd-electron molecules. These molecules are quite stable and paramagnetic in nature”.

Some examples of such molecules and ions are given below:

He^+_2 [He \cdots He]^+, O_2, NO_2, NO


Characteristics and Conditions of the Formation of Three Electrons Bond:


  •  If has been found that three electrons bond can never be formed if electronegativity difference exceed 0.5.
  • Three electrons bond must have larger bond length as compared to two electrons bond and must possess less bond energy
  •  This type of bond forms hybrid between two extreme structures.

A \bullet : B \leftrightarrow : \bullet B


  •   Three electrons bond molecules have tendency to dimerize.
  •  The three electrons bond is half of an electron pair bond.
  • An odd bond is mostly equivalent to 1/2 normal electron pair bond.




(i)  He^+_2 ion: the helium cation (He^+_2) exhibits two resonance form (I) and (II)

He : \bullet He^+ \leftrightarrow He^+ \bullet : He

I                                         II

The binding energy of the He^+_2 ion is \text{kcal mol}^{-1}


(ii) O_2 mole: generally oxygen molecule is represented as:


According to this structure, oxygen molecule should be diamagnetic, while oxygen molecule is paramagnetic which shows the presence of two unpaired electrons hence oxygen molecule may be represented as:


Since in this structure, there are two three electrons bonds hence such molecule is called “double-odd molecule”. This structure also confirms the presence of two unpaired electrons.


(iii) NO_2 molecule: two resonating structures having three electron bond may be written as:

Three electron bond

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