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What are hybridisation states of each carbon atom in the following compounds? CH₂=C=O, CH₃CH=CH₂, (CH₃)₂CO, CH₂=CHCN, C₆H₆

Correct Answer

(C₆H₆) All six carbon atoms are sp2sp^2 hybridised.

(CH₂=C=O) The carbon in CH2\text{CH}_2 is sp2sp^2 hybridised and the central carbon is spsp hybridised.

(CH₂=CHCN) The carbons are sp3sp^3 (if any, but here none), sp2sp^2, sp2sp^2, and spsp hybridised respectively from left to right (CH2\text{CH}_2 is sp2sp^2, CH\text{CH} is sp2sp^2, C\text{C} in CN\text{CN} is spsp).

((CH₃)₂CO) The two carbons in the CH3\text{CH}_3 groups are sp3sp^3 hybridised, and the carbon in CO\text{CO} is sp2sp^2 hybridised.

(CH₃CH=CH₂) The carbon in CH3\text{CH}_3 is sp3sp^3, and the two carbons in CH=CH2\text{CH}=\text{CH}_2 are sp2sp^2 hybridised.

Exercise: EXERCISES | Q: 8.1
For More Understanding

Explanation

The hybridisation of a carbon atom depends on the number of sigma bonds and lone pairs around it. A carbon with four single bonds is sp3sp^3 hybridised, with one double bond is sp2sp^2 hybridised, and with a triple bond or two double bonds is spsp hybridised. The textbook context confirms these states for similar molecules, such as sp3sp^3 and sp2sp^2 for (CH3)2CO(\text{CH}_3)_2\text{CO} and sp3,sp2,sp2,spsp^3, sp^2, sp^2, sp for CH3CH=CHCN\text{CH}_3\text{CH}=\text{CHCN}.

Solution Steps

  1. Step 1: For CH2=C=O\text{CH}_2=\text{C}=\text{O}, the first carbon has one double bond (sp2sp^2) and the central carbon has two double bonds (spsp).

  2. Step 2: For CH3CH=CH2\text{CH}_3\text{CH}=\text{CH}_2, the first carbon has four single bonds (sp3sp^3), while the next two carbons each have one double bond (sp2sp^2).

  3. Step 3: For (CH3)2CO(\text{CH}_3)_2\text{CO}, the methyl carbons are sp3sp^3 hybridised and the carbonyl carbon is sp2sp^2 hybridised.

  4. Step 4: For CH2=CHCN\text{CH}_2=\text{CHCN}, the first two carbons have double bonds (sp2sp^2) and the carbon in the CN\text{CN} group has a triple bond (spsp).

  5. Step 5: For C6H6\text{C}_6\text{H}_6 (benzene), each carbon is bonded to two other carbons and one hydrogen with alternating double bonds, making all carbons sp2sp^2 hybridised.

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