Stretching Force Constant of the Carbonyl Bond in Unconjugated Ketones

Abstract

The secular equation derived for the normal frequencies of a Y-shaped C2CO model can be used with fair accuracy to obtain the carbonyl bond force constant from the measured carbonyl frequency of any symmetrical ketone if the carbon-carbon force constant and the bond angles are known or can be reasonably assigned. The narrow spread of carbonyl frequencies observed for unconjugated ketones, with assumed ``normal'' angles and carbon-carbon force constant, indicates a nearly constant carbonyl stretching force constant in the range 10.2±0.3 (×105 dynes/cm). This value should be equally reliable for unsymmetrical unconjugated ketones. In formaldehyde, the calculated force constant is usually above 12.5 units.