The keto form predominates at equilibrium for most ketones. However, the enol form is important for some reactions because the deprotonated enolate form is a strong nucleophile. The equilibrium is strongly thermodynamically driven, and at room temperature the keto form is favored. The interconversion can be catalyzed by the presence of either an acid or a base. Keto-enol tautomerism : The interconversion between the two forms can be catalyzed by an acid or a base.
Both ketones and aldehydes can be identified by spectroscopic methods. They display strong CO absorption bands near cm In NMR spectroscopy, the carbonyl hydrogen shows a strong absorption peak, and any coupling to protons on the alpha carbon will also show strong signals. Ketones and aldehydes can both be readily reduced to alcohols, usually in the presence of a strong reducing agent such as sodium borohydride.
In the presence of strong oxidizing agents, they can be oxidized to carboxylic acids. As electrophiles, they are subject to attack by nucleophiles, meaning they participate in many nucleophilic addition reactions. Carboxylic acids are organic acids that contain a carbon atom that participates in both a hydroxyl and a carbonyl functional group.
Carboxylic acids are a class of molecules which are characterized by the presence of one carboxyl group. Acids with two or more carboxylic groups are called dicarboxylic, tricarboxylic, etc.
Salts and esters of carboxylic acids are called carboxylates. Carboxylate ions are resonance-stabilized. This increased stability leads to increased acidity compared to that of alcohols. Carboxylic acids act as both hydrogen bond acceptors, due to the carbonyl group, and hydrogen bond donors, due to the hydroxyl group.
As a result, they often participate in hydrogen bonding. Carboxylic acids are polar molecules; they tend to be soluble in water, but as the alkyl chain gets longer, their solubility decreases due to the increasing hydrophobic nature of the carbon chain. Hydrogen bonding between carboxylic acids : Carboxylic acids hydrogen bond with themselves, giving them an increased level of stability. Carboxylic acids can be characterized by IR spectroscopy; they exhibit a sharp band associated with vibration of the C-O bond between and cm Additionally, a broad peak appears in the to cm -1 region.
By 1 H NMR spectroscopy, the hydroxyl hydrogen appears in the 10—13 ppm region, although it is often either broadened or not observed owing to exchange with traces of water.
Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives. As such, they are often produced industrially on a large scale. Carboxylic acids are generally produced from oxidation of aldehydes and hydrocarbons, and base catalyzed dehydrogenation of alcohols.
They can be produced in the laboratory for small scale reactions via the oxidation of primary alcohols or aldehydes, oxidative cleavage of olefins, and through the hydrolysis of nitriles, esters, or amides.
Carboxylic acids are widely used as precursors to produce other compounds. Upon exposure to a base, the carboxylic acid is deprotonated and forms a carboxylate salt.
They also react with alcohols to produce esters and can undergo reduction reactions by hydrogenation or the use of reducing agents. There are also various specialized reactions that carboxylic acids participate in that lead to the formation of amines, aldehydes, and ketones. Esters are functional groups produced from the condensation of an alcohol with a carboxylic acid, and are named based on these components.
Esters are derivative of carboxylic acids where the hydroxyl OH group has been replaced by an alkoxy O-R group. They are commonly synthesized from the condensation of a carboxylic acid with an alcohol:.
Esters are ubiquitous. Most naturally occurring fats and oils are the fatty acid esters of glycerol. Esters are typically fragrant, and those with low enough molecular weights to be volatile are commonly used as perfumes and are found in essential oils and pheromones. Polymerized esters, or polyesters, are important plastics, with monomers linked by esteric units like this:. Ester names are derived from the parent alcohol and acid. Ethyl ethanoate : The name ethyl ethanoate is derived from the components from which it is synthesized: ethanol and ethanoic acid.
In this diagram, the red part of the molecule represents the portion formerly attributed to ethanol minus a H , and the green part of the molecule represents the ethanoic acid portion minus an OH.
Esterification is a form of dehydration synthesis, so the H and OH components are removed as water. In the case of esters formed from common carboxylic acids, more colloquial terms are sometimes used.
For example, butyl acetate, systematically known as ethanoic acid, is derived from butanol and acetic acid and would be written CH 3 CO 2 C 4 H 9. Cyclic esters are known as lactones. Esters contain a carbonyl center, which gives rise to degree C-C-O and O-C-O bond angles due to sp 2 hybridization. Unlike amides, esters are structurally flexible functional groups because rotation about the C-O-C bonds has a lower energy barrier. Their flexibility and low polarity affects their physical properties on a macroscopic scale; they tend to be less rigid, leading to a lower melting point, and more volatile, leading to a lower boiling point, than the corresponding amides.
The pK a of the alpha-hydrogens, or the hydrogens attached to the carbon adjacent to the carbonyl, on esters is around 25, making them essentially non-acidic except in the presence of very strong bases. Esters are more polar than ethers, but less so than alcohols. They participate in hydrogen bonds as hydrogen bond acceptors, but cannot act as hydrogen bond donors, unlike their parent alcohols and carboxylic acids. This ability to participate in hydrogen bonding confers some water-solubility, depending on the length of the alkyl chains attached.
Since they have no hydrogens bonded to oxygens, as alcohols and carboxylic acids do, esters do not self-associate. Consequently, esters are more volatile than carboxylic acids of similar molecular weight.
Esters are usually identified by gas chromatography, taking advantage of their volatility. This peak changes depending on the functional groups attached to the carbonyl. Esters react with nucleophiles at the carbonyl carbon. The carbonyl is weakly electrophilic, but is attacked by strong nucleophiles such as amines, alkoxides, hydride sources, and organolithium compounds.
The C-H bonds adjacent to the carbonyl are weakly acidic, but undergo deprotonation with strong bases. This process is the one that usually initiates condensation reactions. The carbonyl oxygen is weakly basic less so than in amides , but can form adducts with Lewis acids. Amines are compounds characterized by the presence of a nitrogen atom, a lone pair of electrons, and three substituents. The amine functional group contains a basic nitrogen atom with a lone pair of electrons.
As such, the group is derivative of ammonia, in which one or more hydrogen atoms have been replaced by a carbon-containing substituent. Amine groups bonded to an aromatic conjugated cyclic structure are known as aromatic amines.
The aromatic structure effectively decreases the alkalinity of the amine, while the presence of the amine group significantly decreases the reactivity of the ring due to an electron donating effect. An organic compound with multiple amino groups is called a diamine, triamine, tetramine, etc. Amines are generally organized into categories based on their bonding environments.
Amines that have one of their three hydrogen atoms replaced by an alkyl or aromatic substituent are referred to as primary amines.
Secondary amines are those that have two substituents and one hydrogen bonded to a nitrogen. Tertiary amines are amines whose hydrogens have been completely replaced by organic substituents. Finally, cyclic amines are those in which the nitrogen has been incorporated into a ring structure, effectively making it either a secondary or tertiary amine.
The general structure of an amine contains a nitrogen atom, a lone pair of electrons, and three substituents. However, it is possible to have four organic substituents on the nitrogen, making it an ammonium cation with a charged nitrogen center.
Tertiary amine : The central carbon is attached to an amine group and three other carbon atoms. Amines are able to hydrogen bond.
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Please enable JavaScript to access the full features of the site or access our non-JavaScript page. Issue 17, From the journal: Physical Chemistry Chemical Physics.
You have access to this article. Please wait while we load your content Something went wrong. Try again? Cited by. They are readily absorbed through the skin, and workers must exercise caution when handling these compounds. The amide functional group has an nitrogen atom attached to a carbonyl carbon atom. If the two remaining bonds on the nitrogen atom are attached to hydrogen atoms, the compound is a simple amide.
If one or both of the two remaining bonds on the atom are attached to alkyl or aryl groups, the compound is a substituted amide. Simple amides are named as derivatives of carboxylic acids. Amides can be produced when carboxylic acids react with amines or ammonia in a process called amidation. A water molecule is eliminated from the reaction, and the amide is formed from the remaining pieces of the carboxylic acid and the amine note the similarity to formation of an ester from a carboxylic acid and an alcohol discussed in the previous section :.
The reaction between amines and carboxylic acids to form amides is biologically important. It is through this reaction that amino acids molecules containing both amine and carboxylic acid substituents link together in a polymer to form proteins. The carbonyl carbon-to-nitrogen bond is called an amide linkage. This bond is quite stable and is found in the repeating units of protein molecules, where it is called a peptide linkage. Amides are pervasive in nature and technology as structural materials.
The amide linkage is easily formed, confers structural rigidity, and resists hydrolysis. Nylons are polyamides , as are the very resilient materials Aramid , Twaron , and Kevlar.
Amide linkages constitute a defining molecular feature of proteins , the secondary structure of which is due in part to the hydrogen bonding abilities of amides. Amide linkages in a biochemical context are called peptide bonds when they occur in the main chain of a protein and isopeptide bonds when they occur to a side-chain of the protein.
Proteins can have structural roles, such as in hair or spider silk , but also nearly all enzymes are proteins. Many drugs are amides, including paracetamol , penicillin and LSD. Moreover, plant N - alkylamides have a wide range of biological functionalities.
Paracetamol acetaminophen LSD Lysergic diethylamide. Looking back at the various cyclic hydrocarbons discussed previously, we see that all the atoms in the rings of these compounds are carbon atoms. Many heterocyclic compounds are important in medicine and biochemistry. Some compose part of the structure of the nucleic acids, which in turn compose the genetic material of cells and direct protein synthesis. Many heterocyclic amines occur naturally in plants. Like other amines, these compounds are basic.
Caffeine is a stimulant found in coffee, tea, and some soft drinks. Its mechanism of action is not well understood, but it is thought to block the activity of adenosine, a heterocyclic base that acts as a neurotransmitter, a substance that carries messages across a tiny gap synapse from one nerve cell neuron to another cell.
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