Can anyone please briefly explain to me the concept of backbonding along with necessary conditions for backbonding with some example? As I understand, backbonding is a donation of electron from electron-rich to vacant orbital, but I don't know anything else.

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    $\begingroup$ Related 1, 2. $\endgroup$
    – Jan
    Feb 10 '17 at 16:44

BF3 orbitals

$\ce{BF3}$ has trigonal plannar structure all the three $\ce{B-F}$ bonds lie in plane and thus p-orbitals of boron and fluorine become parallel.

Boron has empty p-orbital and p-orbital of fluorine contains lone pair, and hence boron acts as Lewis acid and fluorine as Lewis base. Fluorine donates its lone pair to boron and this bonding is called backbonding.

  • $\begingroup$ It is rough diagram not exact one $\endgroup$
    – user41111
    Feb 10 '17 at 17:04
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    $\begingroup$ But why? Why does Flourine donate its lone pair to Boron? What good is it doing for fluorine? $\endgroup$
    – Piano Land
    Apr 4 '18 at 6:23
  • $\begingroup$ @PianoLand, Formation of an extra bond( even if partial) is exothermic i.e releases energy and stabilizes our system. Hence it is a sort of resonance amongst Boron and Three Fluorine atoms. Hope it helps. $\endgroup$
    – user206007
    May 26 '19 at 10:29
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    $\begingroup$ @user206007 While your input is appreciated, please don't post your comments as answers — as soon as you have enough reputation (50 points), you'll be able to fully participate in comment section. $\endgroup$
    – andselisk
    May 26 '19 at 10:34
  • $\begingroup$ @user206007 From resonance perspective we should not expect a double bond because boron gains negative formal charge. $\endgroup$
    – Anton
    Aug 26 at 11:15

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