Electron Deficient Compounds
Definition and meaning of Electron Deficient Compounds in chemistry.
Electron deficient compounds are molecules whose central atom lacks enough valence electrons to form a conventional two-electron covalent bond to every neighboring atom, leaving it with an incomplete octet or forcing electrons to be shared among more than two atoms at once.
In more detail
The deficiency arises for elements such as boron and beryllium, which have too few valence electrons for the number of bonds they typically form; boron's three valence electrons cannot each supply a bonding pair to four surrounding atoms. Such compounds often compensate by acting as strong Lewis acids, accepting a lone pair from a donor molecule to complete the octet, or by delocalizing a bonding pair over three atoms in a three-center two-electron (3c-2e) bond, as in the boron hydrides. This electron deficiency underlies their high reactivity and their importance as catalysts and reagents in organic synthesis.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Representative formula | B2H6 (diborane) |
| Cause | Central atom (e.g., boron, 3 valence electrons) cannot supply a bonding pair to every neighbor |
| Compensating bonding motif | Three-center two-electron (3c-2e) bond |
Diborane (B2H6) is the classic electron deficient compound: its 12 valence electrons cannot form the seven ordinary two-center bonds needed to link two BH3 units, so the two boron atoms are instead joined by two bridging B-H-B three-center two-electron bonds.
Frequently asked questions
Does 'electron deficient' mean the whole molecule has too few electrons overall?
No, it refers to the central atom specifically lacking a full octet or enough electron pairs for a bond to every neighbor, not an overall shortage of electrons in the molecule.
Why is BF3 electron deficient but SF6 is not?
In BF3 the boron atom has only six valence electrons around it (an incomplete octet), whereas sulfur in SF6 achieves a stable expanded octet of twelve electrons, so SF6 is hypervalent rather than electron deficient.