Which of the following will not be stable?
Let's roll back a little bit. What is the electronic configuration of carbon?
So, carbon has 4 electrons in its valence shell.
Therefore, it can make four covalent bonds to achieve the stable octet configuration.
→Now, In case of CH3
Only 3 electrons will covalently bond with Hydrogen, so one electron will be left and the octet configuration will not be attained.
→ In case of C2H
We know, carbon can covalently bond with carbon.
But, carbon can make maximum three covalent bonds with carbon. [Why?]
Because it doesn't have enough atomic orbitals pointing in the right direction
[* Try to make quadruple bond between two carbon using the shapes of orbitals]
is not possible
C ≡ C−H is possible
because octet configuration of one carbon atom is not achieved. So, not stable.
This is stable because 4 electrons of carbon will be covalently bonded with four Hydrogens.
This is stable because carbon will make three covalent bonds with the other carbon and one bond each with two Hydrogens.
H−C ≡ C−H