Question

which structures below are plausible resonance contributors for scn? assume the connectivity is as written.
answer:
a i and ii
b i and iii
c i and iv
d ii and iii
e ii and iv

Explanation:

• For resonance structures, the connectivity (atom order) must remain the same. Structure IV has a different connectivity (the triple bond is between C and N instead of S and C as in the original \(SCN^-\) connectivity assumption). So IV is not a valid resonance contributor.
• Structure III has a negative charge on S. But considering formal charges, structure I (\(:\overset{+}{S}\equiv C-\overset{:\ :}{N}:^{- 2}\)) and II (\(:\overset{:\ :}{S}=C=\overset{:\ :}{N}:^{-}\)) have more reasonable charge distributions compared to III (where S having a negative charge is less favorable in terms of electronegativity and typical bonding patterns for \(SCN^-\) resonance).

Answer:

A. I and II