Question

Which of the following can act as Lewis acid?

• A. $Si{F}_4$
• B. $SnC{l}_4$
• C. $CC{l}_4$
• D. $S{F}_4$

Answer 1

Answer: (A), (B), (D)

$Si{F}_4$
$SnC{l}_4$
$S{F}_4$

• Lewis Acid: A species that accepts an electron pair (i.e., an electrophile) and will have vacant orbitals.
• Lewis acids accept an electron pair. Lewis Acids are electrophilic meaning that they are electron attracting. When bonding with a base the acid uses its lowest unoccupied molecular orbital
• Various species can act as Lewis acids. All cations are Lewis acids since they are able to accept electrons. (e.g., $C{u}^{2+},F{e}^{2+},F{e}^{3+}$)
• An atom, ion, or molecule with an incomplete octet of electrons can act as an Lewis acid (e.g., $B{F}_3,Al{F}_3$).
• Molecules where the central atom can have more than 8 valence shell electrons can be electron acceptors due to the presence of empty d-orbitals, and thus, are classified as Lewis acids (e.g., $SiB{r}_4,Si{F}_4,SnC{l}_4,S{F}_4$).
• Molecules that have multiple bonds between two atoms of different electronegativities (e.g., $C{O}_2,S{O}_2$)
• But in $CC{l}_4$ there is no vacant d-orbitals available for carbon.
  
• Hence options A,B & D are correct.