<Li> Infrared spectroscopy: the C =O double bond absorbs infrared light at wavenumbers between approximately 1600--1900 cm (5263 nm to 6250 nm). The exact location of the absorption is well understood with respect to the geometry of the molecule . This absorption is known as the "carbonyl stretch" when displayed on an infrared absorption spectrum . In addition, the ultraviolet - visible spectra of propanone in water gives an absoption of carbonyl at 257 nm . </Li> <Li> Nuclear magnetic resonance: the C =O double - bond exhibits different resonances depending on surrounding atoms, generally a downfield shift . The C NMR of a carbonyl carbon is in the range of 160 - 220 ppm . </Li>

Explain why carboxylic acid and esters are not classified as carbonyl compounds