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Chemical Bonding and Molecular Structure question

2007 · Shift 0 · Q32
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  5. /2007 · Shift 0 · Q32

Chemical Bonding and Molecular Structure question

2007 · Shift 0 · Q32

JEE MainChemistryChemical Bonding and Molecular StructureMCQ+4 / −1
Which of the following hydrogen bonds is the strongest?
  1. A
    O−H…….N
  2. B
    F−H…….F
  3. C
    O−H…….O
  4. D
    O−H…….F
View written solutionFree

Correct answer: B

  1. Principle of hydrogen bond strength

    A hydrogen bond is generally stronger when:

    • the bonded atom to hydrogen is very electronegative,
    • the acceptor atom is also highly electronegative and small,
    • the bond formed is more polar and the donor–acceptor interaction is stronger.

  2. Compare the given hydrogen bonds

    We compare the donor and acceptor atoms:

    • A: O−H⋯N\mathrm{O-H\cdots N}O−H⋯N

      • Donor is O−H\mathrm{O-H}O−H, which is a good H-bond donor.
      • Acceptor is N, which is less electronegative than O and F.
      • So this is strong, but not the strongest.

    • B: F−H⋯F\mathrm{F-H\cdots F}F−H⋯F

      • Donor is F−H\mathrm{F-H}F−H, extremely polar because F is the most electronegative atom.
      • Acceptor is also F, which is very small and highly electronegative.
      • This leads to a very strong hydrogen bond.

    • C: O−H⋯O\mathrm{O-H\cdots O}O−H⋯O

      • Common hydrogen bond, as in water.
      • Strong, but generally weaker than F−H⋯F\mathrm{F-H\cdots F}F−H⋯F because O is less electronegative than F.

    • D: O−H⋯F\mathrm{O-H\cdots F}O−H⋯F

      • Donor is O−H\mathrm{O-H}O−H and acceptor is F.
      • Very strong, but the donor bond O−H\mathrm{O-H}O−H is less polar than F−H\mathrm{F-H}F−H.
      • Hence usually weaker than F−H⋯F\mathrm{F-H\cdots F}F−H⋯F.

  3. Order of strength (general trend)

    A common trend is: F−H⋯F>O−H⋯F≳O−H⋯O>O−H⋯N\mathrm{F-H\cdots F > O-H\cdots F \gtrsim O-H\cdots O > O-H\cdots N}F−H⋯F>O−H⋯F≳O−H⋯O>O−H⋯N

  4. Conclusion

    Therefore, the strongest hydrogen bond among the given options is: F−H⋯F\boxed{\mathrm{F-H\cdots F}}F−H⋯F​

So, the correct option is B.

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