Thiocyanate ion, SCN−, is detected in certain physiological fluids. X-ray crystallographic data reveal that the C–S and C–N bond lengths in isolated SCN− are nearly identical, suggesting electron delocalization.
Address the following tasks related to the bonding in SCN−.
(a) Without drawing any structures, state the total number of valence electrons present in SCN−. Show your calculation.
(b) Draw every valid resonance structure for SCN−, assigning formal charges to all atoms.
(c) Identify which resonance contributor is expected to be the major contributor. Support your answer with at least two arguments that refer explicitly to formal charges and electronegativity.
(d) Use your resonance analysis to predict which atom (S or N) bears the greatest share of negative charge in the resonance hybrid. Explain how this prediction is consistent with the nearly equal C–S and C–N bond lengths reported by crystallography.