Formamide, , exhibits resonance involving the carbonyl carbon, the carbonyl oxygen,…
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Formamide, HCONH2, exhibits resonance involving the carbonyl carbon, the carbonyl oxygen, and the adjacent nitrogen.
Two major resonance structures are given below.
Structure I: H–C(=O)–NH2 (all atoms neutral)
Structure II: H–C(–O−)=NH2+ (oxygen bears –1, nitrogen +1)
Spectroscopic evidence suggests that Structure I contributes 75 % and Structure II contributes 25 % to the overall resonance hybrid.
(a) Redraw Structures I and II, including all lone-pair electrons and formal charges.
(b) For each structure, verify the formal charge on C, O, and N. Show your calculations.
(c) Using the percentage contributions given, calculate the weighted average bond order of (i) the C–O bond and (ii) the C–N bond in formamide. Show all steps.
(d) Rank the C–O bond in formamide, a standard C=O double bond, and a typical C–O single bond in order of increasing bond length, providing a brief justification based on the bond orders you obtained.