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JEE Main202331 Jan 2023Evening ShiftChemistryp Block Elements (Group 13 & 14)Actual

The Lewis acid character of boron tri halides follows the order:

Options

  1. ABCl 3 > BF 3 > BBr 3 > Bl 3
  2. BBl 3 > BBr 3 > BCl 3 > BF 3
  3. CBBr 3 > Bl 3 > BCl 3 > BF 3
  4. DBF 3 > BCl 3 > BBr 3 > Bl 3

Correct answer

B. Bl 3 > BBr 3 > BCl 3 > BF 3

Step-by-step solution

The strength of the acidic character of boron trihalides depends upon π - π back bonding. In boron trihalides, π - π -back bonding occurs due to empty orbital of boron and filled orbitals of halogens. The π - π back bonding is shown maximum by BF 3 , as the size of B and F are small and comparatively same. Due to this effect tendency of accepting lone-pair of electrons of boron decreases as the size of halogen increases. The order of size of halogens are F   <   Cl  

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