What is odd electron bond? How can we determine which compound is having odd electron bond?

Bonds with one or three electrons can be found in species, which have an odd number of electrons. The simplest example of a 1-electron bond is found in the hydrogen molecular cation, H₂⁺. One-electron bonds often have about half the bond energy of a 2-electron bond, and are therefore called "half bonds". However, there are exceptions: in the case of dilithium, the bond is actually stronger for the 1-electron Li₂⁺ than for the 2-electron Li₂. This exception can be explained in terms of hybridization and inner-shell effects.^[5]

The simplest example of three-electron bonding can be found in the helium dimer cation, He₂⁺, and can also be considered a "half bond" because, in molecular orbital terms, the third electron is in an anti-bonding orbital which cancels out half of the bond formed by the other two electrons. Another example of a molecule containing a 3-electron bond, in addition to two 2-electron bonds, is nitric oxide, NO. The oxygen molecule, O₂ can also be regarded as having two 3-electron bonds and one 2-electron bond, which accounts for its paramagnetism and its formal bond order of 2.^[6]

Molecules with odd-electron bonds are usually highly reactive. These types of bond are only stable between atoms with similar electronegativities.