Which of the following is the most likely Lewis structure of nitrosyl chloride, NOCl?

Options

A. `underset(..)overset(..)Cl=overset(..)N-overset(..)underset(..)O:`
B. `:overset(..)underset(..)Cl-overset(..)N=overset(..)underset(..)O`
C. `overset(..)underset(..)Cl=N=overset(..)underset(..)O`
D. `:overset(..)underset(..)Cl-N-=O:`

Answer

B

Explanation

Valence shell electron configurations of N, O, and Cl are `2s^2 2p^3`, `2s^2 2p^4`, and `3s^2 3p^5`, respectively. Thus, there are `5+6+7` or `18` valence electrons to account for in `NOCl`. Structures (3) and (4) are ruled out because they have 16 valence electros. Both (1) and (2) have 18 valence electrons and satisfy the octet rule. However, Lewis structure (1) is less plausible because it has `+1` formal charge on `Cl` and `-1` formal charge on O atom:
`overset(+):overset(..)(Cl)=N-overset(..)underset(..)(O)overset(-)( : )`
A positive formal charge on such an electronegative element is quite unlikely and the double bond to chlorine does not occur when it is attached to less or equally electronegative atoms.