Paragraph: The amount of energy required to break a bond is same as the amount of energy released when the…

Paragraph: The amount of energy required to break a bond is same as the amount of energy released when the same bond is formed. In gaseous state, the energy required for homolytic cleavage of a bond is called Bond Dissociation Energy (BDE) or Bond Strength. BDE is affected by $s$-character of the bond and the stability of the radicals formed. Shorter bonds are typically stronger bonds. BDEs for some bonds are given below:




Question: Correct match of the $\mathbf{C}-\mathbf{H}$ bonds (shown in bold) in Column $\mathbf{J}$ with their BDE in Column $\mathbf{K}$ is
  1. P-iii, Q-iv, R-ii, S-i
  2. P-i, Q-ii, R-iii, S-iv
  3. P-iii, Q-ii, R-i, S-iv
  4. P-ii, Q-i, R-iv, S-iii

Solution

Relative stability of radicals :

C∙sp≡CH>C∙Hsp2=CH2>C∙H2−Phsp3 Resonance stabilized>C∙HCH32sp3

So, BDE

  H−C≡CH H−CH=CH2 H−CH2−Ph H−CHCH32
BDE 132 110 88 95

Electronegativity ∝ % s- character

                             ∝ bond strength

                              ∝ BDE

Asked in: JEE Advanced 2021 (Paper 2)

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