Question

In which of the following molecules all atoms are not coplanar?

• A.
  

B.

C.

D.

Answer 1

Hint- In order to deal with this question we will use the basic concept of organic chemistry which states that when a carbon atom is $s{p}^2$ or $sp$ hybridized, all the atoms attached to it are in a plane. In this question we will proceed further by understanding when carbon is said to be $sp/s{p}^2/s{p}^3$.

Complete answer:
$sp$ : The third possible arrangement for carbon is sp hybridization which occurs when carbon is bound to two other atoms (two double bonds or one single + one triple bond).
$s{p}^2$ : carbon is said to be $s{p}^2$ hybridized when it is DOUBLY BONDED with any 1 atom and SINGLY BONDED with any other 2 atoms.
$s{p}^3$ : The term “ $s{p}^3$ hybridization” refers to the mixing character of one 2s-orbitals and three 2p-orbitals to create four hybrid orbitals with similar characteristics. In order for an atom to be $s{p}^3$ hybridized, it must have an s orbital and three p orbitals
We know that when a carbon atom is $s{p}^2$ or $sp$ hybridized, all the atoms attached to it are in a plane.
All the carbon atoms in compounds A, C and D are $s{p}^2$ hybridized. Hence, in these molecules, all the atoms are coplanar.
In option B, one carbon atom is $s{p}^3$ hybridized. It has tetrahedral geometry. Hence, in this molecule, all atoms are not coplanar.

So, the correct answer is option B.


Note- Coplanar means atoms or groups of atoms that lie on the same plane. Like biphenyl, it has both benzene rings on the same plane. When all atoms of a compound are in the same plane are called coplanar compounds. Co planarity in organic compounds is seen in unsaturated molecules.