Organic Nitrogen Compounds
There is a tremendous variety of organicRefers to the branch of chemistry that studies compounds containing carbon, usually in combination with hydrogen and other elements such as O, N, S, and P. Certain small ions and compounds containing carbon (such as carbonate ions and carbon dioxide) are not considered to be organic, but rather are classed as inorganic. compounds which can be derived from carbon, hydrogen, and oxygen which is evident from the numerous previous sections discussing these compounds. If we include nitrogen as a possible constituent of these molecular structures, many more possibilities arise. Most of the nitrogen-containing compounds are less important commercially, however, and we will only discuss a few of them here.
Amines may be derived from ammonia by replacing one, two, or all three hydrogens with alkyl groups. Some examples are
The terms primary (one), secondary (two), and tertiary (three) refer to the number of hydrogens that have been replaced. Both primary and secondary amines are capable of hydrogen bonding with themselves, but tertiary amines have no hydrogens on the electronegative nitrogen atomThe smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume..
Amines usually have unpleasant odors, smelling “fishy“. The three methylamines listed above can all be isolated from herring brine. Amines, as well as ammonia, are produced by decomposition of nitrogen-containing compounds when a living organism dies. The methylamines are obtained commercially by condensationThe process in which a liquid forms from gas or vapor of the same substance. A chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. of methanol with ammonia over an aluminum oxide catalystA substance that increases the rate of a chemical reaction but that undergoes no net change during the reaction.:
Dimethylamine is the most important, being used in the preparation of herbicides, in rubberA tough, elastic polymer obtained from the juices of certain tropical plants; a synthetic material having similar properties. vulcanizationA process for increasing the strength and hardness of rubber by heating the rubber in the presence of sulfur., and to synthesize dimethylformamide, an important solventThe substance to which a solute is added to make a solution..
Amides are another important nitrogen containing organic compound. The key feature of an amine is a nitrogen atom bonded to a carbonylThe functional group consisting of a carbon atom doubly bonded to an oxygen atom; found in aldehydes and ketones. carbon atom. Like esters, amides are formed in a condensation reactionA chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. An example is formation of an ester from a carboxylic acid and an alcohol.. While esters are formed from the condensation reaction of an alcoholAn organic compound containing the functional group -OH. and a carboxylic acidAn organic compound containing the functional group -C(=O)OH., amides are formed from the condensation of an amine and a carboxylic acid:
This general reaction is usually unfavorable, because the hydroxyl groupThe functional group of an oxygen atom bonded to an hydrogen atom, -OH; found in alcohols. acts as a bad leaving group. Organic chemists have devised methods to workA mechanical process in which energy is transferred to or from an object, changing the state of motion of the object. around this by using certain chemicals to activate the carboxylic acid and allow for the addition of the amine.
As amides are formed by condensation reactions, many important condensation polymers involve amide linkages. NylonAny of several human-made polyamide fibers; polyamides are formed by condensation of an amine group with a carboxylic acid group., for instance, is formed from the amide condensation of hexamethylenediamine and adipic acid.
A second set of condensation polymers formed from amide linkages are the proteins and peptides found in your body and in all organisms. These polymers are formed from another organic nitrogen compound, the amino acidA carboxylic acid containing an amino group (-NH2). In an alpha amino acid, the amino group is attached to the carbon atom adjacent to the carboxyl group.. These molecules contain both an amine group and a carboxyl group. Examples of such amino acids are glycine and lysine:
Amino acids are the constituents from which proteins are made. Some, like glycine, can be synthesized in the human body, but others cannot. Lysine is an example of an essential amino acid—one which must be present in the human diet because it cannot be synthesized within the body. As mentioned, the condensation of amino acids into peptides forms amide linkages. For this reason, scientists sometimes refer to the amide backbone of a protein or peptide. A protein has a long series of amide bonds, as can be seen in the following figure showing the synthesisFormation of substances with more complicated sturctures than do their precursors. of a tri-peptide from three amino acids:
The intermolecular forces and boiling points of nitrogen-containing organic compounds may be explained according to the same principles used for oxygen-containing substances.
EXAMPLE Rationalize the following boilingThe process of a liquid becoming vapor in which bubbles of vapor form beneath the surface of the liquid; at the boiling temperature the vapor pressure of the liquid equals the pressure of the gas in contact with the liquid. points: (a) 0°C for CH3CH2CH2CH3; (b) 11°C for CH3CH2OCH3; (c) 97°C for CH3CH2CH2OH; and (d) 170°C for NH2CH2CH2OH.
SolutionA mixture of one or more substances dissolved in a solvent to give a homogeneous mixture. All four molecules have very similar geometries and the same number of electrons (26 valence electrons plus 8 core electronsAny electrons in filled subshells within inner shells of an atom.), and so their London forces should be about the same. Compound (a) is an alkaneA hydrocarbon containing only single bonds between carbon atoms. and is nonpolarDescribes a molecule with no net permanent dipole; this can occur when there is no separation of centers of positive and negative electrical charge or because there are bond dipoles that cancel each others' effects. A polar molecule will assume certain orientations more than others in an electric field.. By contrast compound (b) is an etherAn organic compound containing the functional group R-O-R'. and should be slightly polar. This slight polarity results in a slightly higher boiling point. Compound (c) is isomeric with compound (b) but is an alcohol. There is hydrogen bonding between molecules of (c), and its boiling point is much higher. Molecule (d) has both an amino groupThe functional group of a nitrogen atom bonded to two hydrogen atoms, -NH2; found in amines and amino acids. and a hydroxyl group, each of which can participate in hydrogen bonding. Consequently it has the highest boiling point of all.