Aldehyde

"Aldehydes and ketones are among the most important of all functional groups, both in the chemical industry and in biological pathways. ... Aldehydes are normally prepared in the laboratory by oxidation of primary alcohols or by partial reduction of esters."

"In conclusion, the conjugate umpolung of α,β-unsaturated aldehydes represents a versatile and powerful method to synthesize different cyclic products such as β- and γ-lactones and cyclopentenes. More valuable applications based on the NHC-catalyzed umpolung are expected to be discovered in due course."

"The carbonyl group in aldehydes and ketones is an oxygen analog of the carbon–carbon double bond. However, the electronegativity of oxygen polarizes the pbond, thereby rendering the acyl substituent electron withdrawing. The arrangement of bonds around the carbon and oxygen is planar, a consequence of sp2 hybridization."

"In the NMR spectra of aldehydes and ketones, the formyl hydrogens and the carbonyl carbons show strong deshielding. The carbon – oxygen double bond in ketones gives rise to a strong infrared band at about 1715cm-1, which is shifted to lower frequency by conjugation and to higher frequency in aldehydes and small rings. The ability of nonbonding electrons to be excited into the π* molecular orbitals causes the carbonyl group to exhibit characteristic, relatively long-wavelength UV absorptions. Finally, aldehydes and ketones fragment in the mass spectrometer by α cleavage and McLafferty rearrangement."