# 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.

Examples

(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:

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