Organic Chemistry
Organic chemistry is a branch of chemistry that studies the structure, properties and reactions of organic compounds. Organic compounds include Hydrocarbons, Alcohols and Ethers, carboxylic acids, esters, amines and amides. At your level, more emphasis will be placed on some but not all of these organic compounds.
Organic compounds are a significant component of earthly life and constitute the majority of known pharmaceutical and petrochemical products. The bonding patterns of carbon, with its valence of four electrons, its ability to form single, double and triple bonds, make the array of organic compounds very diverse, and a wide range of applications.
Neutral organic compounds tend to be hydrophobic; i.e. they are less soluble in water than in organic solvents. Some exceptions include organic compounds that contain ionizable groups as well as low molecular weight alcohols, amines, and carboxylic acids where hydrogen bonding occurs. Organic compounds tend to dissolve in organic solvents although their solubility varies widely with the organic solute and with the organic solvent.
Organic compounds can undergo melting and boiling. The melting and boiling points correlate with the polarity of the molecules and their molecular weight. Some organic compounds can undergo sublimation, i.e. they can evaporate without melting. (from solid to gas states, bypassing the liquid phase).
There are five distinct structural representations of the organic compounds. The example below is Butane. The left-most structure is a bond-line drawing where the hydrogen atoms are removed. The 2nd structure has the hydrogens added depicted-the dark wedged bonds indicate the hydrogen atoms are coming toward the reader, the hashed bonds indicate the atoms are oriented away from the reader, and the solid (plain) ponds indicate the bonds are in the plane of the screen/paper. The middle structure shows the four carbon atoms. The 4th structure is a representation just showing the atoms and bonds without 3-dimensions. The right-most structure is a condensed structure representation.
Classification of Organic compounds can be achieved by combining several approaches as follows:
Functional groups are important in organic chemistry because they determine the chemical and physical properties of the compounds. Alcohols, for example, have the subunit C-O-H while carboxylic acids have the -COOH group.
The example above shows the -COOH functional group found in carboxylic acids such as acetic acid.
The aliphatic hydrocarbons are subdivided into three groups of homologous series according to their degree of saturation at the C-C bond:
1. Alkanes (paraffins): Are saturated, they only contain single bonds, i.e. just C-C, C-H.
2. Alkenes (olefins): These contain one or more double bonds and are therefore unsaturated.
3. Alkynes (acetylenes): These are also unsaturated and contain one or more triple bonds.
Both saturated and unsaturated compounds exist as cyclic derivatives. Saturated cyclic compounds contain single bonds only, whereas aromatic rings have an alternating double bond.
Aromatic hydrocarbons contain conjugated/alternating double bonds. The most important example is benzene as shown below.
The structure of Benzene. (Source: Wikipedia-CC BY-SA 3.0)
A heterocyclic compound is a cyclic compound that has atoms of at least two different elements as members of its ring(s) Rings can fuse with other rings on an edge to give polycyclic compounds. Purine (the nucleoside base) is a notable polycyclic aromatic heterocycle.
There are two main groups of polymers: synthetic polymers and biopolymers. Synthetic polymers are artificially manufactured, and are commonly referred to as industrial polymers. Biopolymers occur within natural environments.
Alkanes occur in homologous series, each successive compound differs from the one before it only by a CH2. The General Formula for Alkanes is Cn H2n + 2. Alkanes are named by adding a suffix -ane at the end of name. The number of carbons is given by a 'prefix' as follows:
Alkanes can be linear (as shown above) or branched. The following are the steps to follow when naming alkanes:
Isomers are compounds with the same formula but a different arrangement of atoms in the molecule, which result in different properties.
The above compounds all have the same molecular formula (C5H12) but differ in their structural formula due to the presence of branch chains. From left is pentane, followed by 2-methylbutane and the image on the right is 2,2-dimethylpropane. (Source: Wikipedia-CC BY-SA 3.0)
Non-polar molecules, which are less dense than water. Alkanes are immiscible with water making two layers.
Van-der Waals or dipole-dipole attractive forces, and not H-bonding (as in polar molecules) are the main intermolecular forces
These weak intermolecular forces operate over small distances, arising because the electron distribution within molecules at any given instance is not uniform. Resulting in tiny electrical attractions between molecules.
These temporary dipoles hold alkanes as liquids or solids, and must be overcome in order to vaporize a liquid or melt a solid (wax)
As their description implies, they contain one or more rings. Simple cycloalkanes have a prefix "cyclo-" to distinguish them from alkanes. Cycloalkanes are named as per their acyclic counterparts with respect to the number of carbon atoms in their backbones, e.g., cyclopentane (C5H10) is a cycloalkane with 5 carbon atoms just like pentane (C5H12), but they are joined up in a five-membered ring. In a similar manner, propane and cyclopropane, butane and cyclobutane, etc. They have the general formula CnH2n
Alkenes are unsaturated hydrocarbons that contain a carbon-carbon double bond. Unsaturated hydrocarbons containing two or more double bonds are known as alka(di)enes, alka(tri)enes, alka(tetra)enes, and so on. (Actual names should exclude the parentheses). The physical properties of alkenes are similar to those of alkanes, they are colorless, nonpolar, and combustible. Their physical state depends on molecular mass i.e. the simplest alkenes (ethene, propene, and butene) are gases at room temperature. Linear alkenes of approximately five to sixteen carbons are liquids, and higher alkenes are waxy solids. The melting point of the solids also increases with increase in molecular mass. Alkenes have a stronger smell than their corresponding alkanes.
Alkenes are relatively stable compounds, but are more reactive than alkanes, mostly because of the presence of the C-C double bond. The most common reactions that can occur are:
Hydrogenation
This is an addition reaction to result in the corresponding alkane.
CH2=CH2 + H2 -> CH3CH3.
Hydration
Hydration, the addition of water across the double bond of alkenes, yields alcohols.
CH2=CH2 + H2O -> CH3-CH2OH
Halogenation
The addition of bromine or chlorine to alkenes
CH3-CH=CH2 + HBr -> CH3-CH2-CH2-Br
Oxidation
In the presence of oxygen, alkenes burn with a bright flame to produce carbon dioxide and water.
Naming Side Chains
Naming alkenes. (Source: Wikipedia-CC BY-SA 3.0)
Alkynes are unsaturated hydrocarbons containing at least one carbon-carbon triple bond. The simplest alkyne with no other functional group forms a homologous series with the general chemical formula CnH2n-2. Alkynes can also undergo hydrogenation, halogenation and hydration, among other reactions.
The suffix -yne is used to denote the presence of a triple bond.
Aromatic hydrocarbons contain alternating double (conjugated) bonds. This means that every carbon atom in the ring is sp2 hybridized, allowing for added stability. The most important example is benzene - C6H6.
Fractionation (or fractional distillation) is the process of physically separating the components of a mixture of compounds based on the differences in their boiling points. The compounds with the lowest boiling points are made up of the smallest molecules. These have fewer electrons and weaker London forces compared with larger molecules. To get to the next level, the vapors are forced through condensed liquid in each tray. When the temperature of the liquids in a tray is below the boiling point of a particular compound, that compound condenses and is collected.
Below is a schematic flow diagram of a typical crude oil distillation unit. The incoming crude oil is preheated by exchanging heat with some of the hot, distilled fractions and other streams.
Crude oil refining. (Source: Wikipedia-CC BY-SA 3.0)
Fractionation alone does not produce enough of the hydrocarbons that are in market demand, so further chemical refining is performed.
Cracking is a chemical process where large molecules are broken down into smaller molecules. There are two types of Cracking: thermal cracking - using high temperatures and pressures, and catalytic cracking - Uses a catalyst and reduces the need for extreme temperatures and pressures.
Hydrocracking involves the combination of catalytic cracking and hydrogenation.
Catalytic reforming is the chemical process that converts aliphatic molecules in a gasoline fraction to aromatic gasoline molecules, such as the conversion of heptane to methylbenzene.
Alkylation is the process of converting an aliphatic molecule into its branched isomer, therefore it can also be called Isomerization, for example haptane to 2,4 dimethylpentane.
Complete Combustion: When a hydrocarbon reacts with oxygen to produce carbon dioxide and water vapor as the only chemical products. This reaction requires excess oxygen otherwise if oxygen is limited, it results in incomplete combustion. Incomplete combustion results in other products such as carbon monoxide and carbon (soot).
Another common physical process is solvent extraction - the addition of a solvent to selectively dissolve and remove a specific compound.
Organic halides are hydrocarbon derivatives formed when one or more hydrogen atoms are replaced by an element or a group of elements other than hydrogen, usually the Halogens (F2, Cl2, Br2, I2). Halides can be classified as Haloalkanes-compounds with carbon atoms linked by single bonds, haloalkenes-compounds with one or more double bonds between carbon atoms and haloaromatics-compounds with carbons linked in one or more aromatic rings with a delocalized doughnut.
When naming the halogen the -ine ending is replaced by -o such as:
Example:
CH2BrCHBrCH2CH2CH3 is named 1,2-dibromopentane.
CH3- CCl = CCl- CH3 is named 2,3-dichlorobut-2-ene.
CH3- CCl2 - CCl2- CH3 is named 2,2,3,3-tetrachlorobutane.
Alcohols can be regarded as derivatives of water in which one or two of the H atoms has been replaced by a hydroxyl group. The functional group in alcohols is the -OH, hydroxyl group and should be bound to a saturated carbon atom. Simple alcohols such as methanol and ethanol have the general formula is CnH2n+1OH.
There are several ways to produce alcohols.
Hydration: Some low molecular weight alcohols of industrial importance are produced by the addition of water to alkenes. Ethanol, isopropanol, 2-butanol, and tert-butanol are produced by this general method.
Biological: Ethanol is obtained by fermentation using glucose produced from sugar from the hydrolysis of starch, in the presence of yeast and temperature of less than 37 oC to produce ethanol.
Substitution: Alkyl halides react with aqueous NaOH or KOH mainly to produce alcohols.
Hydrolysis
Solubility: Because of the presence of the OH group, Methanol and Ethanol are polar molecules and form hydrogen bonding, therefore are soluble in water. As the number -OHs increases so does solubility in water.
The boiling point increases with chain length and number of -OHs
There are three different types of alcohols depending on the number of R-groups. R- groups represent the carbon chain(s).
The above figure represent primary alcohols (1 R-group), Secondary alcohols (2 R-groups) and tertiary alcohols (3 R-groups). (Source: Wikipedia-CC BY-SA 3.0)
(This content is obtained from Britannicca.com - no copyright infringement intended )
Alcohol is the oldest and still one of the most widely used drugs. Wines and beers have been brewed by several hundred preliterate societies. The importance of these alcoholic beverages is evident and its availability is ubiquitous in almost every social gathering. Alcoholic beverages were thus probably discovered accidentally. Fermentation can occur in any sugar/starch-containing food-such as grapes, grains, berries, or honey—left exposed in warm air. Yeasts from the air act on the sugar, converting it to alcohol and carbon dioxide.
For a long time, alcohol has acted mostly as a symbolic announcer of friendship, peace, and agreement, in personal as well as in business or political relations. Alcohol has some nutritional value and could be used as medicine for some illnesses and especially for relieving pain. Alcohol has also been used to facilitate religious rituals and communion among some religious groups.
In modern society, however, many people discover that drinking can often help them to suppress the overwhelming inhibitions, shyness, anxieties, and tensions that frustrate and interfere with urgent needs to function effectively, either socially or economically. In cultures characterized by various inhibitions against gratifying interpersonal relationships, the capacity of alcohol to serve as a social lubricant is highly valued.
Modern societies has trouble around many issues of right and wrong or proper and improper behaviour. The modern conflict over drinking reflects the complex interactions of the individual with small groups and larger society. Small groups, formed by common interests in business, occupation, recreation, neighbourhood, politics, ethnicity, or religion, use communal drinking to facilitate mixing, engender solidarity, reduce normal inhibitions against trust and promote collaboration with 'strangers,' symbolize and ratify accord, and ensure that gatherings for celebration will succeed as festive occasions. Individuals use alcoholic beverages as an agreeable effector of desired mood alteration, such as altering dysphoric mood or masking unease and pain, and to enable participation in the various small groups with which they are required to associate.
The acute effects of a large intake of alcohol are well known. Mental impairment starts when the blood concentration is about 0.05 percent. A concentration of alcohol in the blood of 0.40 percent usually causes unconsciousness, and 0.50 percent can be fatal. Accidents and violence, which are often alcohol-related, are major causes of death for young persons. Women who drink during pregnancy risk physical and mental damage to their babies (fetal alcohol syndrome). Alcohol also can interact dangerously with a variety of medications, such as tranquilizers, antidepressants, and pain relievers.
Chronic alcohol consumption carries with it significant risks as well: liver disease; pancreatitis; suicide; hemorrhagic stroke; mouth, esophageal, liver, and colorectal cancers; and probably breast cancer. In alcoholics, nutritional impairment may result from the displacement of nutrient-rich food as well as from complications of gastrointestinal dysfunction and widespread metabolic alterations.
The social and economic costs of alcoholism and heavy drinking are essentially incalculable. The annual costs of health and welfare services provided to alcoholics and their families in the United States alone is in the billions of dollars and suggests the measure of effects worldwide. Furthermore, the millions of problem drinkers who have jobs and businesses are more frequently absent and often less efficient than their occupational associates. Almost a quarter of all patients in general hospitals are estimated to be alcoholic, and their per capita cost is more than twice that of other patients.
Carboxylic acids are characterized by a -COOH group attached to the R-group. The O atoms in COOH are not attached together, rather are both attached to the C, one as a OH (Hydroxyl) group, and the other as a double bond O i.e. a carbonyl group C=O.
The functional group of carboxylic acids. (Source: Wikipedia-CC BY-SA 3.0)
The boiling point increases as the molecule size increases due to increased van der Waals forces. In addition, carboxylic acids tend to have higher boiling points than water, because of their greater surface areas and their tendency to form stabilized dimers through hydrogen bonds. For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporized.
Solubility: Carboxylic acids are soluble in organic solvents and also in water due to hydrogen bonding. Small ones dissolve easily in cold water but as the molecule size increases, the solubility decreases.
Oxalic acid (Rhubarb) and lactic acid are simple carboxylic acids that are quite prevalent in nature.
Formic acid has an acrid odor and a biting taste, and is responsible for the sting of some types of ants.
Acetic acid is the sour component of vinegar.
Butanoic acid is an oxidation product that contributes to the disagreeable smell of body odor. It's common name, butyric acid, is derived from the Latin word butyrum, meaning 'butter', because butyric acid gives rancid butter its peculiar odor and taste.
Esters are formed by the reaction between an alcohol + carboxylic acid. For example, Ethanol + Ethanoic acid produce Ethyl Ethanoate.
As you notice from the example above, esters are named from the original alcohol and carboxylic acid.
The functional group of esters. (Source: Wikipedia-CC BY-SA 3.0)
Esters are used for flavoring. For example:
Polymers are large molecules made by linking together many smaller molecules, called monomers. Natural polymers include proteins, carbohydrates and lipids, while synthetic polymers include plastics, nylon, acetate, and polyesters.
Polymerization reactions can be categorized as addition reactions or as condensation reactions. Addition polymerization occurs when reactive monomers unite without forming any other products. Usually this involves the addition of one monomer at a time. Condensation polymerization occurs by joining reactive monomers and producing a molecule of water.
Polyethene
As the name suggests, polyethene is a polymer of ethene (C2H4) monomers. Low density polyethylene (LDPE) is made by causing the long chains of ethylene to branch. That way they cannot lie next to each other, which reduces the density and strength of the polyethylene. This makes the plastic lighter and more flexible. Low density polyethylene is used to make things like plastic bags, plastic wrap, and squeeze bottles. When the carbon chains get up to 500,000 carbons long, they are tough enough for synthetic ice, replacement joints, and bullet-proof vests. This is called high density polyethylene (HDPE).
The ethene monomer (Source: Wikipedia-CC BY-SA 3.0)
Polypropene (Polypropylene)
Propylene is similar to ethene but it replaces one H with a CH3. Polypropylene is used to make things like carpet, rope and thermal underwear.
The propylene monomer (Source: Wikipedia-CC BY-SA 3.0)
Polyvinyl Chloride (PVC)
Vinyl chloride (the monomer) has the formula CH2=CHCl. PVC is one of the most widely used polymers, with dozens of practical applications including PVC pipes, house sidings, raincoats, PVC fencing, windows etc.
The vinyl monomer (Source: Wikipedia-CC BY-SA 3.0)
Polystyrene
When a benzene ring is attached to an ethene molecule, it is commonly called styrene. Polystyrene is used to make Styrofoam used in disposable cups, plates, packing materials etc.
The styrene monomer (Source: Wikipedia-CC BY-SA 3.0)
Teflon
Teflon is also called Polytetrafluoroethylene (PTFE), as the name suggests, contains tetraflouroethylene monomers. It's used for non stick coating such as nonstick cookware. There are recent concerns that teflon might release toxic chemicals when heated at high temperatures.
The tetrafluoroethylene monomer (Source: Wikipedia-CC BY-SA 3.0)
Condensation reactions can be summarized as monomer X + monomer Y -> Polymer + small molecule (usually water but can also be HCl or NH3). These are common in biological systems, but there are synthetic analogs that mimic the same processes. For example, polyesters mimic Lipids, nylon mimics proteins while cellulose polymers mimic long chain carbohydrates. These in general are referred to as functional analogs. They can be developed and used to mimic naturally occurring polymers such as artificial sweeteners.
Nylons
Nylons are formed by the condensation of aliphatic diacids with aliphatic diamines. Nylon was synthesized as a substitute for silk, a natural polyamide.
Polyesters
A polyester is a series of ester molecules joined in a long chain. The reaction can be summarized as Dicarboxylic acid + polyalcohol -> polyester + water.
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