Question

What is the hybridisation of carbon atoms in \(CH_{2}=CH-CN\) (Acrylonitrile)?

• A. \(C_{1}=sp^{3},\;C_{2}=sp^{3},\;C_{3}=sp\)
• B. \(C_{1}=sp^{2},\;C_{2}=sp^{2},\;C_{3}=sp\)
• C. \(C_{1}=sp^{2},\;C_{2}=sp,\;C_{3}=sp^{2}\)
• D. All carbon atoms are \(sp^{2}\) hybridised.

Hint:

Remember these hybridisations: \[ \boxed{ \begin{aligned} C=C &\rightarrow sp^2\\ C\equiv C &\rightarrow sp\\ C\equiv N &\rightarrow sp\\ C-C &\rightarrow sp^3 \end{aligned} } \] In nitriles (\(-C\equiv N\)), the carbon atom is always \(sp\)-hybridised.

Answer 1

The Correct Option is B

Concept: Hybridisation depends upon the steric number (number of \(\sigma\)-bonds and lone pairs) around the atom. \[ \boxed{ \begin{aligned} sp &\rightarrow 2 \text{ electron domains (linear)}\\ sp^2 &\rightarrow 3 \text{ electron domains (trigonal planar)}\\ sp^3 &\rightarrow 4 \text{ electron domains (tetrahedral)} \end{aligned} } \] The structure of acrylonitrile is \[ CH_2=CH-C\equiv N. \] The carbon atom of the nitrile group forms a triple bond with nitrogen and is therefore \(sp\)-hybridised.

Step 1: Determine the hybridisation of the first carbon.
The first carbon is \[ CH_2. \] It is involved in one double bond and two single bonds. Hence, it has three electron domains. Therefore, \[ \boxed{C_1=sp^2.} \]

Step 2: Determine the hybridisation of the second carbon.
The second carbon is attached by

• one double bond,

• one single bond to the nitrile carbon,

• one single bond to hydrogen.
Thus, it also has three electron domains. Hence, \[ \boxed{C_2=sp^2.} \]

Step 3: Determine the hybridisation of the nitrile carbon.
The third carbon is \[ C\equiv N. \] It forms

• one triple bond with nitrogen,

• one single bond with carbon.
Therefore, it possesses two electron domains. Hence, \[ \boxed{C_3=sp.} \] Thus, the hybridisation is \[ \boxed{ C_1=sp^2,\; C_2=sp^2,\; C_3=sp. } \] Therefore, \[ \boxed{\textbf{Option (B)}} \] is the correct answer.