Resonance Effects. Part 3: Formyl Chloride, HCOCl.
The CO stretching vibration is strong and highly characteristic for
carbonyl compounds. Substitution of one of the H-atoms by another atom or
group X, affects the frequency of the CO stretching vibration in HCOX.
If X is a pi-donating group, then resonance will weaken the CO bond and
cause the frequency of the CO stretching vibration to be lowered.
The molecules H2C=O, HCOOH, HCOCl and HCONH2
nicely exemplify the effect of resonance.
Look for their CO stretching frequencies in
the output files behind the links "Freqs".