Overview

Organic compounds can readily be subdivided into several distinct categories, depending on their constituents or functional groups. The hydrocarbons contain only carbon and hydrogen, while there are also many organic compounds containing oxygen, as well as nitrogen and sulfur.

Compounds containing a single-bonded oxygen atom include the alcohols (containing the -OH functional group), ethers, and epoxides. Compounds containing a a double-bonded oxygen atom include the aldehydes, ketones (all of which contain the carbonyl functional group -C=O) as well as the carboxylic acids (which contain the carboxyl functional group -COOH). Derivatives of the carboxylic acids include the acyl halides (with a carbonyl group and also a halogen group), acid anhydirdes, esters and amides (all of which contain a carbonyl group attached to an oxygen or another strong electrophilic group or element). Compounds containing nitrogen include the amines (or alkaloids, single-bonded N), nitriles (triple-bonded N) and nitro compounds (-NO2 functional group). Compounds containing sulfur include the thiols and sulfides.   

I. Hydrocarbons

The hydrocarbons are compounds composed entirely of carbon and hydrogen. The largest  class of hydrocarbons by far is the aliphatics.  Aliphatic hydrocarbons are further subdivided into families: alkanes, alkenes, alkynes, and their cyclic analogs. Alkanes have a single-bonded carbon framework, alkenes have a backbone consisting of double-bonded carbons, and alkynes contain triple-bonded carbons. These three aliphatic families can then be subdivided into those that have open, straight or branched chains of single-bonded carbon atoms (the acyclics) and their cyclic analogs which have a closed chain. The alicyclics include the  cycloalkanes, cycloalkenes, and cycloalkynes. 

Alternatively, the aromatics consist of alternating single and double bonds in a hexagonal 6-membered carbon ring, which comprises their basic molecular building block. Another name for the aromatics is the arenes. Aptly named, the aromatics were originally obtained by chemical treatment of pleasant smelling plant extracts. 

The main groups are listed below followed by an example (chemical formula and name) as well as their characteristic reaction types.

Alkanes are not considered to have a functional group, although reactions that replace a hydrogen atom can occur, and are known as substitution reactions. The most typical of these is halogenation, as described in the previous section on methane. In general , though, the hydrogen atoms in an alkane are relatively unreactive and any other group attached to the tetrahedral hydrocarbon framework will be the functional group, R.

The double bond is a functional group in an alkene, the triple bond a functional group in an alkyne, and the benzene ring itself is a functional group in an arene (or aromatic compound). 

II. Halogen-substituted derivatives

Much of the chemistry of methane involves free radical chain reactions, which take place under vigorous conditions and usually yield a mixture of products. The same is true for the rest of the alkane family. 

Preparation of alkyl halides. A reactive particle - typically an atom or free radical - is needed in order to begin the attack on the alkane molecule. It is the generations of this reactive particle that requires the vigorous conditions, e.g. the dissociation of a halogen molecule into atoms. In its attack, the reactive particle abstracts hydrogen form the alkane. The alkane itself is thus converted into reactive particle (or free radical) which continues on in the chain of the reaction sequence until a halogen-substituted alkane derivative is formed: an alkyl halide. 

Preparation of alkenyl halides. Alternatively, alkenyl halides (e.g. chloroethane) are formed by the reaction of a hydrogen halide (e.g. HCl) with a member of the triple-bonded alkyne family (e.g. acetylene, C2H2). See a detailed description under Alkyne reactions.

Aromatics. Aryl halides are far more common than alkenyl halides. These are compounds i in which a halogen substituent is attached directly to one of the 6 conjugated carbon atoms in an aromatic ring. Due to a hybridization of C-H and C-Cl (or C-F, C-Br, etc.) ) bonds, the C-H bonds of aryl halides are both shorter and stronger than the C-H bonds of alkyl halides. In this respect, they are more similar to vinyl (alkenyl) halides than alkyl halides. 

The strength of their C-H bonds causes aryl halides to react very slowly in reactions in which C-H bond cleavage is rate-determining (e.g. nucleophilic substitution) . Examples of reactions that do take take place at reasonable rates proceed by mechanisms distinctly different from the classical SN1 and SN2 pathways.  

Preparation of aryl halides. The main method is via the halogenation of the aryl compounds known as the alkyl benzenes. The benzylic position in alkylbenzenes is analogous to the allylic position in alkenes. Due to electron delocalization, a benzylic (or allylic) C-H bond is weaker than an alkyl C-H bond, making it more vulnerable to attack by a free radical. The comparative ease with which a benzylic hydrogen is abstracted leads to a high selectivity in free-radical halogenation of alkylbenzenes. Thus , for example, the chlorination of toluene takes place exclusively at the benzylic carbon and is an industrial process for the preparation of both dichloro and trichloro benzene. For more details, see Aromatic reactions. Benzylic bromination is a more commonly used laboratory procedure than chlorination and is typically carried out in an non-polar organic solvent (e.g. CCl4) near 80 degrees C under conditions of photochemical initiation.  

In addition, the side chain in alkylbenzenes is alkane-like, and should undergo halogenation as alkanes do. This free-radical substitution reaction requires conditions of intense heat or light under which halogen atoms are formed. The ring is benzene-like and should undergo substitution as benzene does: via electrophilic substitution. The position of hydrogen attack (whether in the side-chain or somewhere on the ring itself) is governed largely by the experimental conditions: temperature, light and/or acid catalyst.      

III. Alcohols

If, as an organic chemist, you were allowed to choose the ten aliphatic compounds with which to be stranded on a desert island, you would be strongly advised to pick all alcohols - -based on their wide spectrum of chemical versatility. Using them as precursors, you could synthesize nearly every other kind of aliphatic compound: alkyl halides, alkenes, ethers, aldehydes, ketones, acids, esters, as well as many others.  

From the alkyl halides, you could make Grignard reagents, and from the reaction between these and the aldehydes and ketones obtain more complicated alcohols, and so on. On your desert island, you could use your alcohols not only as raw materials, but frequently as the solvents in which reactions are carried out and from which products are re-crystallized. Finally, hot and tired after a long day in the tropical laboratory, you could refresh yourself with an (isopropyl) alcohol rub and perhaps relax over a cool (ethyl) alcohol drink. 

Alcohols are organic compounds that contain the hydroxyl group (-OH) as their functional group. The general formula for an alcohol is R-OH. Alcohols are among the most polar organic compounds because the hydroxyl OH group is strongly polar and can easily participate in hydrogen bonding. Thus, the simplest alcohols (e.g. methyl alcohol or methanol, ethyl alcohol or ethanol) are completely miscible in water. Ethyl alcohol is sometimes called "grain alcohol" because it is produced by the fermentation of grain or other organic material. Isopropyl alcohol is the common name for 2-propanol, used as rubbing alcohol. Yeast acts on sugars to produce ethanol and carbon dioxide (CO2). In baking, the same reaction utilizes the CO2 to make dough rise, and the alcohol is evaporated.  

The oxidation of alcohols produces the aldehydes, ketones and carboxylic acids. These compounds are extremely important to us, and their preparation by the oxidation of alcohols is an essential part of organic synthesis.

For alcohols to be such important starting materials in aliphatic chemistry, they must not only be versatile in their reactions but also available in large quantities at low prices. There are number of different methods for synthesizing alcohols, several of which care described in detail in the section on Alcohols.

Methanol, ethanol, and isopropyl alcohol all have one hydroxide group per molecule. An alcohol with two hydroxyl groups per molecule is called a glycol. Ethylene glycol is the major component of antifreeze. An alcohol with three hydroxyl groups per molecule is called a glycerol. Glycerol is a building block of fat molecules and a by-product in the manufacture of soap. It is added to toothpastes, lotions, and some candies in order to retain moisture and softness.

Phenols are compounds of the general formula ArOH, where Ar is a phenyl, substitutes phenyl, or some other aromatic group. Phenols differ from alcohols in having the -OH group attached directly to the aromatic ring. Both alcohols and phenols can be converted into ethers and esters. In most of their properties, however, and in their preparations, the two kinds of compound differ so greatly that they well deserve to be classified as different families.

IV. Ethers  &  Epoxides

Ethers are composed of two alkyl groups bonded to an oxygen atom. The general formula for an ether is R - O - R'. (The symbol R' represents another alkyl group, either the same as or different from the first.) Like alcohols, ethers are much more polar than hydrocarbons. Ethers have no O-H hydrogens, however, so they cannot hydrogen bond with themselves. 

Diethyl ether is the most common ether used for starting engines in cold weather. It is a highly volatile liquid, which revolutionized the field of pain-killing anesthesia in the middle 1800’s. This was before the discovery of the localized effects of liquid cocaine, and the subsequent discovery of more effective methods combining a barbiturate (e.g. sodium pentathol) to induce sleep and nitrous oxide (NO) for its analgesic properties. Today ether is used widely as a laboratory solvent, though it is highly flammable.    

V. Aldehydes, Ketones & Carboxylic Acids

Aldehydes and ketones both have a functional group of a carbon atom doubly bonded to an oxygen atom. This is called a carbonyl group. 

The simplest aldehyde is formaldehyde, which is soluble in water. A 40% solution called formalin is widely used as an embalming agent and to preserve biological specimens. The simplest ketone is acetone, which is an excellent solvent and used commonly to remove paint and nail polish.                                    

Organic acids, or fatty acids, are organic compounds which exhibit acidic properties. Chemically, they are known as carboxylic acids because they contain the carboxyl functional group ( - COOH). Formic acid (CHOOH) is found widely in plant and animals, such as in the sting of bees, ants, and stinging nettles. Acetic acid is formed when ethanol oxidizes, and is found in onions, vinegar, and wine. The sour taste of citric acid is found in many fruits. Lactic acid is found in sour milk, buttermilk, sauerkraut and pickles, and is produced by the body during anaerobic exercise. The simplest series of carboxylic acids are the alkanoic acids, R-COOH where R is a hydrogen atom or an alkyl (CH3) group. Compounds may also have two or more carboxylic acid groups per molecule.

VI. Carboxylic Acid derivatives

Esters are organic compounds formed from an alcohol and an organic acid by the elimination of water (Fig. 8). They are common in both plants and animals, giving fruits and flowers their characteristic odor and taste. The ester amyl acetate has the smell of banana. Esters are also used in perfumes and artificial flavorings.

VII. Nitrogen-containing compounds

VIII. Sulfur-containing compounds