Draw the structure for p -isopropylaniline and classify. Always start with the parent compound: draw the pentane chain. Then attach a methyl group at the third carbon atom and an amino group at the second carbon atom. The ions have one, two, three, and four methyl CH 3 groups attached to a nitrogen atom. Their names are as follows:. Draw the structure for each compound and classify the amine as primary, secondary, or tertiary.
Primary and secondary amines have hydrogen atoms bonded to an nitrogen atom and are therefore capable of hydrogen bonding part a of Figure 5. These amines boil at higher temperatures than alkanes but at lower temperatures than alcohols of comparable molar mass. Tertiary amines have no hydrogen atom bonded to the nitrogen atom and so cannot participate in intermolecular hydrogen bonding.
They have boiling points comparable to those of ethers Table 5. Table 5. All three classes of amines can engage in hydrogen bonding with water part b of Figure 5.
Amines of low molar mass are quite soluble in water; the borderline of solubility in water is at five or six carbon atoms. The simple ones smell very much like ammonia.
Higher aliphatic amines smell like decaying fish. Or perhaps we should put it the other way around: Decaying fish give off odorous amines. The stench of rotting fish is due in part to two diamines: putrescine and cadaverine. They arise from the decarboxylation of ornithine and lysine, respectively, amino acids that are found in animal cells.
For more information about lysine, see Chapter 8 "Amino Acids", Section 8. Aromatic amines generally are quite toxic. They are readily absorbed through the skin, and workers must exercise caution when handling these compounds. CH 3 CH 2 NH 2 because amines can engage in hydrogen bonding with water; alkanes cannot engage in hydrogen bonding. Recall that ammonia NH 3 acts as a base because the nitrogen atom has a lone pair of electrons that can accept a proton.
Nearly all amines, including those that are not very soluble in water, will react with strong acids to form salts soluble in water. Amine salts are named like other salts: the name of the cation is followed by the name of the anion. The cation has two groups—methyl and ethyl—attached to the nitrogen atom. The anion is the acetate ion. Many drugs that are amines are converted to hydrochloride salts to increase their solubility in aqueous solution.
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.
The effective dose of caffeine is about mg, corresponding to about two cups of strong coffee or tea. Nicotine acts as a stimulant by a different mechanism; it probably mimics the action of the neurotransmitter acetylcholine. People ingest this drug by smoking or chewing tobacco.
Its stimulant effect seems transient, as this initial response is followed by depression. Nicotine is highly toxic to animals. It is especially deadly when injected; the lethal dose for a human is estimated to be about 50 mg. Nicotine has also been used in agriculture as a contact insecticide. Cocaine acts as a stimulant by preventing nerve cells from taking up dopamine, another neurotransmitter, from the synapse.
High levels of dopamine are therefore available to stimulate the pleasure centers of the brain. After the binge, dopamine is depleted in less than an hour. This leaves the user in a pleasureless state and often craving more cocaine. Cocaine is used as the salt cocaine hydrochloride and in the form of broken lumps of the free unneutralized base, which is called crack cocaine.
Because it is soluble in water, cocaine hydrochloride is readily absorbed through the watery mucous membranes of the nose when it is snorted. Crack cocaine is more volatile than cocaine hydrochloride. It vaporizes at the temperature of a burning cigarette. When smoked, cocaine reaches the brain in 15 s. Contrast the physical properties of amines with those of alcohols and alkanes. Amines have a lone pair of electrons on the nitrogen atom and can thus act as proton acceptors bases. The solubilities of amines are similar to those of alcohols; the boiling points of primary and secondary amines are similar to those of alcohols; the boiling points of tertiary amines, which cannot engage in hydrogen bonding because they do not have a hydrogen atom on the nitrogen atom, are comparable to those of alkanes.
Heterocyclic compounds are ring compounds with atoms other than carbon atoms in the ring. 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. 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.
For more about peptide linkages, see Chapter 8 "Amino Acids", Section 8. Simple amides are named as derivatives of carboxylic acids. The lower members of the series are soluble in water, with borderline solubility occurring in those that have five or six carbon atoms. Like the esters, solutions of amides in water usually are neutral—neither acidic nor basic.
The amides generally have high boiling points and melting points. These characteristics and their solubility in water result from the polar nature of the amide group and hydrogen bonding Figure 5. Similar hydrogen bonding plays a critical role in determining the structure and properties of proteins, deoxyribonucleic acid [DNA], ribonucleic acid [RNA], and other giant molecules so important to life processes.
Amide molecules can engage in hydrogen bonding with water molecules a. Those amides with a hydrogen atom on the nitrogen atom can also engage in hydrogen bonding b. Both hydrogen bonding networks extend in all directions. The addition of ammonia NH 3 to a carboxylic acid forms an amide, but the reaction is very slow in the laboratory at room temperature. Water molecules are split out, and a bond is formed between the nitrogen atom and the carbonyl carbon atom.
In living cells, amide formation is catalyzed by enzymes. Proteins are polyamides; they are formed by joining amino acids into long chains. In proteins, the amide functional group is called a peptide bond. For more information about proteins, see Chapter 9 "Proteins and Enzymes", Section 9. Just as the reaction of a diol and a diacid forms a polyester see Chapter 4 "Carboxylic Acids, Esters" Section 4.
The two difunctional monomers often employed are adipic acid and 1,6-hexanediamine. The monomers condense by splitting out water to form a new product, which is still difunctional and thus can react further to yield a polyamide polymer.
Some polyamides are known as nylons. Nylons are among the most widely used synthetic fibers—for example, they are used in ropes, sails, carpets, clothing, tires, brushes, and parachutes. They also can be molded into blocks for use in electrical equipment, gears, bearings, and valves. Generally, amides resist hydrolysis in plain water, even after prolonged heating. In the presence of added acid or base, however, hydrolysis proceeds at a moderate rate. In living cells, amide hydrolysis is catalyzed by enzymes.
Amide hydrolysis is illustrated in the following example:. Amides are dehydrated by heating a solid mixture of the amide and phosphorus V oxide, P 4 O Water is removed from the amide group to leave a nitrile group, -CN.
The liquid nitrile is collected by simple distillation. Note: This is a just a flow scheme rather than a proper equation. I haven't been able to find a single example of the use of the full equation for this reaction. In fact the phosphorus V oxide reacts with the water to produce mixtures of phosphorus-containing acids. The Hofmann degradation is a reaction between an amide and a mixture of bromine and sodium hydroxide solution.
Heat is needed. The net effect of the reaction is a loss of the -CO- part of the amide group. You get a primary amine with one less carbon atom than the original amide had. If you started with ethanamide, you would get methylamine. The full equation for the reaction is:. Amides can be reduced to primary amines by reaction with lithium tetrahydridoaluminate, LiAlH 4 , in dry ether ethoxyethane at room temperature. The initial reaction is followed by treatment with dilute acid, such as dilute sulphuric or hydrochloric acid.
You might notice that this is a slightly different reduction from the one that happens when LiAlH 4 reduces the carbon-oxygen double bond in an aldehyde or ketone. In those cases, the oxygen remains in the final molecule, and you get an -OH group formed.
If this is the first set of questions you have done, please read the introductory page before you start. The lack of base character in amides Unusually for compounds containing the -NH 2 group, amides are neutral. For example, if you dissolve these compounds in water, the nitrogen lone pair takes a hydrogen ion from a water molecule - and equilibria like these are set up: Notice that the reactions are reversible. Why doesn't something similar happen with amides? Use the BACK button on your browser to return to this page.
Let's look at the organic compounds that contain nitrogen and their difference in basicity:. Notice that amines are the strongest bases, followed by ammonia, then phenylamine, and finally amides. In general the basicity trend for amines and ammonia is as follows:.
This is due to the electron donating effect of alkyl groups which increase the electron density on nitrogen. Tertiary amines have more electron donating R groups and increase the electron density on nitrogen to a greater extent.
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