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From Wikipedia


The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and commercial names. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes which contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halon.

Haloalkanes have been known for centuries. Ethyl chloride was produced synthetically in the 15th century. The systematic synthesis of such compounds developed in the 19th century in step with the development of organic chemistry and the understanding of the structure of alkanes. Methods were developed for the selective formation of C-halogen bonds. Especially versatile methods included the addition of halogens to alkenes, hydrohalogenation of alkenes, and the conversion of alcohols to alkyl halides. These methods are so reliable and so easily implemented that haloalkanes became cheaply available for use in industrial chemistry because the halide could be further replaced by other functional groups.

While most haloalkanes are human-produced, non-artificial-source haloalkanes do occur on Earth, mostly through enzyme-mediated synthesis by bacteria, fungi, and especially sea macroalgae (seaweeds). More than 1600 halogenated organics have been identified, with bromoalkanes being the most common haloalkanes. Brominated organics in biology range from biologically-produced methyl bromide to non-alkane aromatics and unsaturates (indoles, terpenes, acetogenins, and phenols). Halogenated alkanes in land plants are more rare, but do occur, as for example the fluoroacetate produced as a toxin by at least 40 species of known plants. Specific dehalogenase enzymes in bacteria which remove halogens from haloalkanes, are also known.

Classes of haloalkanes

From the structural perspective, haloalkanes can be classified according to the connectivity of the carbon atom to which the halogen is attached. In primary (1°) haloalkanes, the carbon that carries the halogen atom is only attached to one other alkyl group. An example is chloroethane (CH3CH2Cl). In secondary (2°) haloalkanes, the carbon that carries the halogen atom has two C-C bonds. In tertiary (3°) haloalkanes, the carbon that carries the halogen atom has three C-C bonds.

Haloalkanes can also be classified according to the type of halogen. Haloalkanes containing carbon bonded to fluorine, chlorine, bromine, and iodine results in organofluorine, organochlorine, organobromine and organoiodine compounds, respectively. Compounds containing more than one kind of halogen are also possible. Several classes of widely used haloalkanes are classified in this way Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These abbreviations are particularly common in discussions of the environmental impact of haloalkanes.


Haloalkanes generally resemble the parent alkanes in being colorless, relatively odorless, and hydrophobic. Their boiling points are higher than the corresponding alkanes and scale with the atomic weight and number of halides. This is due to the increased strength of the intermolecular forces—from London dispersion to dipole-dipole interaction because of the increased polarity. Thus carbon tetraiodide (CI4) is a solid whereas carbon tetrafluoride (CF4) is a gas. As they contain fewer C-H bonds, halocarbons are less flammable than alkanes, and some are used in fire extinguishers. Haloalkanes are better solvents than the corresponding alkanes because of their increased polarity. Haloalkanes containing halogens other than fluorine are more reactive than the parent alkanes - it is this reactivity that is the basis of most controversies. Many are alkylating agents, with primary haloalkanes and those containing heavier halogens being the most active (fluoroalkanes do not act as alkylating agents under normal conditions). The ozone-depleting abilities of the CFC's arises from the photolability of the C-Cl bond.


Haloalkanes are of wide interest because they are widespread and have diverse beneficial and detrimental impacts. The oceans are estimated to release 1-2 million tons of bromomethane annually.

A large number of pharmaceuticals contain halogens, especially fl


"Fluorination" redirects here. For the addition of fluoride to drinking water, seewater fluoridation.

Halogenation is a chemical reaction that incorporates a halogen atom into a molecule. More specific descriptions exist that specify the type of halogen: fluorination, chlorination, bromination, and iodination.

In a Markovnikov addition reaction, a halogen like bromine is reacted with an alkene which causes the π-bond to break forming an haloalkane. This makes the hydrocarbon more reactive and bromine as it turns out, is a good leaving group in further chemical reactions such as nucleophilic aliphatic substitution reactions and elimination reactions.

Several main types of halogenation exist, including:

Likewise in dehalogenation a halogen atom is removed from a molecule as a result of a reaction.


The formation of gold(III) chloride by the chlorination of gold.

Specific halogenation methods are the Hunsdiecker reaction (from carboxylic acids) and the Sandmeyer reaction (arylhalides).

An example of halogenation can be found in the organic synthesis of the anesthetic halothane from trichloroethylene which involves a high temperature bromination in the second step :


Trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. Many trihalomethanes find uses in industry as solvents or refrigerants. THMs are also environmental pollutants, and many are considered carcinogenic. Trihalomethanes with all the same halogen atoms are called haloforms.

Table of common trihalomethanes

Industrial uses


Trifluoromethane and chlorodifluoromethane are both used as refrigerants in some applications. Trihalomethanes released to the environment break down faster than chlorofluorocarbons (CFCs), thereby doing much less damage to the ozone layer (if they contain chlorine). Chlorodifluoromethane is a refrigerant HCFC, or hydrochlorofluorocarbon, while fluoroform is an HFC, or hydrofluorocarbon. Fluoroform is not ozone depleting.

Unfortunately, the breakdown of trihalomethane HCFCs does still result in the creation of some free chlorine radicals in the upper atmosphere and subsequent ozone destruction. Ideally, HCFCs will be phased out entirely in favour of entirely nonchlorinated refrigerants.


Chloroform is a very common solvent used in organic chemistry. It is a significantly less polar solvent than water, well-suited to dissolving many organic compounds.

Although still toxic and potentially carcinogenic, chloroform is significantly less harmful than carbon tetrachloride. Because of the health and regulatory issues associated with the use of carbon tetrachloride, in modern chemistry laboratories chloroform is used as a cheaper, cleaner alternative wherever possible.

Water pollutants

Trihalomethanes are formed as a by-product predominantly when chlorine is used to disinfect water for drinking. They represent one group of chemicals generally referred to as disinfection by-products. They result from the reaction of chlorine and/or bromine with organic matter present in the water being treated. The THMs produced have been associated through epidemiolgical studies with some adverse health effects. Many governments set limits on the amount permissible in drinking water. However, trihalomethanes are only one group of many hundreds of possible disinfection by-products-the vast majority of which are not monitored-and it has not yet been clearly demonstrated which of these are the most plausible candidate for causation of these health effects. In the United States, the EPA limits the total concentration of the four chief constituents (chloroform, bromoform, bromodichloromethane, and dibromochloromethane), referred to as total trihalomethanes (TTHM), to 80 parts per billion in treated water.

Chloroform is also formed in swimming pools which are disinfected with chlorine or hypochlorite in the haloform reaction with organic substances (e.g. urine, sweat, hair and skin particles). Some of the THMs are quite volatile and may easily vaporize into the air. This makes it possible to inhale THMs while showering, for example. The EPA, however, has determined that this exposure is minimal compared to that from consumption. In swimmers uptake of THMs is greatest via the skin with dermal absorption accounting for 80% of THM uptake. Exercising in a chlorinated pool increases the toxicity of a "safe" chlorinated pool atmosphere with toxic effects of chlorine byproducts greater in young swimmers than older swimmers.

From Yahoo Answers

Question:Hi, it is taking me a while to figure this out. I just am not sure! Identify a haloalkane and describe the manner in which it functions as an anesthetic.

Answers:We meet again =) Ha, this one is tough though. I found this on the web as it is. Not sure if its correct, I have no idea! Here it is: Haloalkanes are a group of chemical compounds that consist of an alkane with one or more halogens attached to it. Some examples of haloalkanes useds as anethesia are Halothane, Trichloroethylene, and Chloroform. The exact manner in which anesthetics works is, for the most part, still uncertain at the cellular and molecular levels. There are two big theories, however, about how this might work. One, called the Meyer Overton theory states that anesthetic chemicals dissolve within the membranes of cells and then causes the structures of these cells to be distorted. This, consequently, impairs the ability of nerve signals to be carried along nerve cells. A second theory states that anethetics interact with specific proteins, such as neurotransmitter receptors and ion channels, and change their structures, thereby, affecting their action. One of the mechanisms describing how chloroform, specifically, works is that it increases the movement of potassium through potassium ion channels in nerve cells. Chloroform has been shown to activate these channels, and this can lead to hyperpolarization of the membranes, which happens to make nerve cells less "excitable," or less able to carry an electrical signal. This can either prevent the release of neurotransmitters, or prevent the response caused by neurotransmitters, or both. Also, chloroform, as well as most of the anesthetic chemicals, can work by increasing the level of the neurotransmitter GABA in the brain. GABA is an inhibitory neurotransmitter, which means that it slows down the conduction of nerve signals. The more GABA that's present, the less efficient the nervous system might be. ----- I'm feeling pretty good that the names of the drugs are indeed haloalkanes. The rest I can't be sure. I feel the answer given is more physiology-orientated, and I'm getting the feeling you wanted a more chemistry-based answer. But thats probably the best I can do for now, this ones out of my league!


Answers:There's really no difference - it's just the way things are named. A haloalkane is where you basically take an alkane, such as methane, and replace one of its hydrogens with a halogen (F, Cl, Br, I). Examples include chloromethane, 1-bromo ethane, 2-iodo propane. A halon is basically a haloalkane, but it uses a code of numbers to describe the haloalkane instead of just simply naming it. A halon uses usually 4 numbers to describe the haloalkane: The 1st number says how many carbons are in the molecule, The 2nd number says the # of fluorine atoms in the molecule, The 3rd number says the # of chlorine atoms, The 4th number says the # of bromine atoms (Sometimes there is a 5th number that indicates the # of iodine atoms present, but it's rare) So for example, the molecule Halon 1121 would have 1 carbon, 1 fluorine, 2 chlorine, and 1 bromine in it. Since carbon makes only 4 bonds with other atoms, the only possible formula for the molecule would be CFCl2Br (or bromodichlorofluoromethane). Hope this helps!

Question:How do Grignard reagents react with alkenes, alkynes and haloalkanes? For example, how would ethyl magnesium bromide react with t-butyl bromide and propyne respectively? Also, what would happen if EtMgBr reacted with 1-bromobut-2-ene? Any clues would be much appreciated!

Answers:Grignard reagents act as nucelophiles and do not react with the unsaturated bonds of alkenes and alkynes. Halogenoalkanes react with magnesium to form Grignard reagents of the form RMgX. Adding another halogenoalkane into the reaction mixture will just form another Grignard reagent R'MgX. In the reaction of 1-bromobut-2-ene with RMgX the bromine atom is replaced by the R group.

Question:How would you write the structural formaulas for methene, ethene, propene, butene, hexene etc etc.. and also for other homologus series like alkynes, haloalkanes. do I have learn all of them, or is there like a systematic way of doing it? Please explain clearly, I am extremely weak in chemistry. Also please correct me if im wrong here: I have sort of worked out how to do the formulas for alkanes, from an example.. is pentane : CH3-CH2-CH2-CH2-CH3 is hexane: CH3-CH2-CH2-CH2-CH2-CH3 Does the 'CH3' always have to come at the end of the chain? I mean what are the rules..my teacher didnt explain clearly Thank you very much

Answers:What you have written is called the condensed structural formula There is no methene as - a double bond takes at least 2 carbons. Ethene is CH2=CH2, yo have propene correct. Butene is CH3-CH2-CH=CH2 , 1 Butene or CH3-CH=CH-CH3, 2 butene. The more carbons, the more isomers. Your pentane and hexane are correct. Remember C has 4 bonds so that is the reason that CH3- is on the end. Check thesource to see some expanded structural formulas.

From Youtube

Mechanism for the Formation of Anti-Markovnikov Haloalkane from alkenes :In this example, we are trying to form 1-bromopropane [Anti-Markovnikov Product] from propene. We are using H-Br as our reactant.