Bifunctional compounds As the word bifunctional implies, compounds with two functional groups. In organic chemistry, when a single organic molecule has two different functional groups, it is called a bifunctional molecule, which has properties of two different types of functional groups.. A bifunctional molecule has the properties of two different types of functional groups, such as an alcohol (-OH), amide (CONH2), aldehyde (-CHO), nitrile (-CN) or carboxylic acid (-COOH). Many bifunctional molecules are used to produce medicines and catalysts, while others are used in condensation polymerization like polyester and polyamide. In organic molecules, functional groups are atoms or molecules that are responsible for the characteristic properties of that molecule, with the exceptions of double and triple bonds, which are also functional groups. Nomenclature of multifunctional compounds: The longest chain containing the suffix is chosen, the priority for choosing the suffix being carboxylic acid, -CO2H, > carboxylic acid derivative, -COX > aldehyde, -CHO > ketone, -CO-, > alcohol, -OH > amine, -NH2. The second and other groups are labelled as substituents. e.g. CH3CH(OH)CH2CO2H is 3- hydroxybutanoic acid; HOCH2CH2CH2COCH3 is 5-hydroxypentan-2-one; CH3CH(OH)CH2C(CH3)(NH2)CH3 is 4-amino-4-methylpentan-2-ol; CH3COCO2H is 2- oxopropanoic acid, (the =O of an aldehyde or ketone is called oxo when it has to be named as a substituent). The carbon-carbon double and triple bonds are always incorporated in the chain, with lower priority than the other groups. [e.g. CH2=CHCH(OH)CH3 is but-3-en-2-ol; CH3C≡CCH2CO2H is pent-3-yn-oic acid.] For compounds with larger carbon skeletons a further condensation of structural may be used. represents propylcyclohexane. Each line represents two carbon atoms joined by a single bond, and hydrogens which are present are not shown. The number of H's is such to satisfy the valency of carbon, 4. Benzene is C6H6 and is the parent of aromatic compounds. Each carbon in the benzene ring has one hydrogen attached. As a second resonance structure with the double bonds in the other three positions can be drawn, the resonance hybrid of benzene is often represented as a hexagon with a circle inside: Note the following rections are they give ideas of bifunctional compounds Keto-enol Tautomerism In organic chemistry, keto–enol tautomerism refers to a chemical equilibrium between a keto form (a ketone or an aldehyde) and an enol (an alcohol). The keto and enol forms are said to be tautomers of each other. The interconversion of the two forms involves the movement of an alpha hydrogen atom and the reorganisation of bonding electrons; hence, the isomerism qualifies as tautomerism. A compound containing a carbonyl group (C=O) is normally in rapid equilibrium with an enol tautomer, which contains a pair of doubly bonded carbon atoms adjacent to a hydroxyl (−OH) group, C=C-OH. The keto form predominates at equilibrium for most ketones. Nonetheless, the enol form is important for some reactions. The deprotonated intermediate in the interconversion of the two forms, referred to as an enolate anion, is important in carbonyl chemistry, in large part because it is a strong nucleophile. Mechanism The acid catalyzed conversion of an enol to the keto form proceeds by a two- step mechanism in an aqueous acidic solution. For this, it is necessary that the alpha carbon atom (the carbon atom closest to the functional group) contains at least one hydrogen atom known as the alpha hydrogen atom. This alpha hydrogen atom must additionally be positioned such that it may line up parallel with the antibonding pi- orbital of the carbonyl group. The hyperconjugation of this bond with the C–H bond at the alpha carbon atom reduces the electron density of the C–H bond and weakens it, making the alpha hydrogen atom more acidic. When the alpha hydrogen atom is not aligned with the pi orbital, for example in the adamantanone or other polycyclic ketones, the enolization is impossible or very slow. In the first step of the mechanism, the exposed electrons of the C=C double bond of the enol are donated to a hydronium ion (H3O+). This addition follows Markovnikov's rule, thus the proton is added to the carbon atom with more attached hydrogen atoms. This is a concerted step with the oxygen atom in the hydroxyl group donating electrons to produce the eventual carbonyl group. Further reading Enols and Enolates .