The characteristic group of carbonyl compounds is carbonyl, consisting of carbon-oxygen double bond. The bond exhibit polarity due to the difference in electrical property, which carbon atom express electropositivity while oxygen atom is electronegative. Thus the carbon atom of the carbonyl can be attacked by electrophile (Lewis acid) and the oxygen atom is able to react with nucleophile (Lewis base) (Fig.1). Other similar reaction about carbonyl group are basically based on this principle of charge deviation. Carbonyl compound is a very broad concept, containing many derivatives such as ketone, aldehyde, acid halide, amide, carboxylic acid, carboxylate ester, haloformate, imide, peroxy ester, thiocarboxy and potential substance with carbonyl (Fig.2).
Fig.1. Reaction of a carbonyl compound with (a) electrophile (Lewis acid) and (b) nucleophile (Lewis base).
Fig.2. Carbonyl group and its derivatives
Carbonyl compounds possess a wide range of physical properties such as pH, solubility and optical property, which are most determined by the substituent group connected with carbonyl group. For instance, carboxylic acid express acidity owing to the movement of hydrogen proton. But generally, the oxygen atom of carbonyl can form hydrogen bond with water, so the carbonyl compounds with simple structure can be mixed with water. Besides, the carbonyl group has a dipole moment, which increases the intermolecular attraction and rises the boiling point than relative alkanes with identical molecular weight. It is noteworthy that carbonyl compounds exist in every aspect of our lives, they are widely distributed in natural products and play a key role in electrochemical application, polymer-manufacture and pharmacological research.
Electrolyte: Taking advantage of the electrical property of the carbonyl, it can participate in a charge transfer process and be utilized as electrolytes. The reversible electrochemical reaction can promote the electrons to attack the carbonyl carbon and generate unstable oxygen, which is combined with Li+ to exhibit remarkable electrochemical behavior. A series of carbonyl compounds have been investigated and applied in electrolytes (Fig.3).
Fig.3. Charge transfer process of varous carbonyl compounds (Adv. Sci. 2019, 6.1900431.)
Pharmacological research: Scientists have investigated the effect of various natural and artificial chalcones. They exhibit excellent anticancer and the apoptotic properties via inducing apoptosis of numerous cancer cells. Related analogues with different pharmacological effect are depicted in Fig 4.
Fig.4. Chemical structure of chalcone derivatives (Eur. J. Med. Chem. 2019, 183, 111687.)
Polymer: Nylon has been widely used in fiber to manufacture colorful clothes. Nylon 66 is fabricated by condensation polymerization between hexanediamine and adipic acid, which amide bond is the basic and valuable constituent unit (Fig.5).
Fig.5. Synthetic procedure of Nylon 66