Why is the reaction of ethene with bromine called an addition reaction

Alkenes react with liquid bromine to give alkyl bromides as the product. This reaction is an electrophilic addition reaction. Two bromine atoms are added to through the double bond of alkene. Liquid bromine is prepared by dissolving Br 2 in carbon tetrachloride CCl 4.

Br 2 is a non-polar molecule and they dissolve in non-polar solvents. If one double exists in the alkene molecule, it reacts with one molecule of Br 2 and two bromine atoms are added to the alkene to form alkyl halide compounds. This reaction proves, alkenes are unsaturated organic compounds. This reaction is the reaction between alkenes and halogens. In this tutorial, we are going to discuss about alkenes reactions with bromine liquid, and mechanisms of these reactions.

We learn ethene and bromine reaction and propene and bromine reaction. Here, we are going to discuss about some reactions and products of liquid bromine and alkenes such as ethene, propene, 2-butene and more. Mechanism of ethene and propene with Br 2 l are explained also.

Ethene is a symmetric alkene molecule. Ethene reacts with liquid bromine to give 1,2-dibromoethane. Ethene and bromine reaction also gives a symmetrical alkyl halide compound. Two bromine atoms are attached to the two carbon atoms in the ethene molecule.

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This reaction can be done at room temperature or below temperatures than room temperature. Addition of bromine to ethene is an electrophilic addition reaction.

Normally, bromine molecule Br 2 is not electron deficiency compound. But due to higher electrons density in the double bond of ethenebromine molecule gets polarized. The positively charged bromine atom electron deficiency atom is attacked by the double bond and make bonds with both carbon atoms of double bond. Other bromine molecule forms a bromide ion. A cyclic brominium ion is given as the intermediate product.

Next, one carbon atom in the brominium ion is attacked by bromide ion Br. Then a bond between Br - and that carbon atom is formed and existing bromine - carbon bond in the ring is broken. A dibromide compound is formed as the only product.

No minor products are given in this reaction. Also it adds to through the pi bond. Hence we call this reaction is an electrophilic addition reaction. Propene reacts with bromine and add two bromine atoms give the 1,2-dibromopropane. Two bromine atoms are added to the double bond carbon. Ethene was a non polar alkene. But propene is a polar molecule.

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This reaction is also an electrophilic addition reaction. First, Br 2 molecule is polarized by alkene bond. With that, electrons in the double bond attacks the positively charged Br atom and forms a cyclic bromonium ion. Other Bromine atom is eliminated as a bromide ion. As second step, produced bromide ion attacks a carbon atom which has a bond with other bromine atom.

Then one of previous carbon - bromine bond is broken and a new carbon - bromine bond forms.The name of the reaction is pretty intuitive. Ethene's double bond is broken which leaves room for bromine to be added to form dibromoethane. The explanation is that from two chemical entities is obtained another by addition Br to ethene.

Electrophilic addition reaction Also, it's a hydration reaction, since you are adding water to the alkene in this case, ethene. Water reacts with ethEne to form ethanol; the reaction is a type of addition reaction called, specifically, hydration. The ethene reacts with the bromine and the solution turns colourless from its original orange colour. The ethene doesnt change from orange to colourless as ethene is already colourless but the bromine water turns from orange to colourless.

Ethene is an unsaturated substance since it is alkene and has one double bond, we can use bromine water to test ethene. Yellow bromine water turns colourless if the substance is ethene. If it is methane which is alkane not alkenebromine will stay yellow. As polyehtene is unsaturated single bond it does not react with bromine and there is no colour change.

But bromine reacts with ethene and it becomes colourless. Ethene has a double bond between the two carbon atom i. Bromine is an electrophile electron deficient species it attacks the Carbon doubble bond and accepts a pair of electrons. Ethene has a very reactive double bond, and if mixed with bromine in organic solvent, it will undergo an addition reaction, where the two bromine atoms will adjoin onto the ethane molecule because the double bond has broken, it now becomes an alkane ethane - more specifically it will form 1,2 - dibromoethane.

This is a useful way of distinguishing between alkanes and alkenes of similar molecular weights. The solution will turn the orange bromine water into a colourless solution.

Yes, however it doesn't require it either to react. This is an addition reaction, as the double carbon-carbon bond in ethene breaks to accomodate the two chlorine atoms. Product is 1,2, dichloroethane. Asked By Curt Eichmann. Asked By Leland Grant. Asked By Veronica Wilkinson. Asked By Daija Kreiger.

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Asked By Danika Abbott. Asked By Consuelo Hauck. Asked By Roslyn Walter. All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply.

Ask Login. Elements and Compounds. Asked by Wiki User. Top Answer. Wiki User Answered Related Questions.Because ethene is an alkene, which is a less stable structure than an alkane. Bromine opens the double bond in ethene, rather than replacing hydrogen.

This gives ethene an alkane structure. Ethene and bromine are an addition reaction because ethene is an alkene - it has a double bond. It is easier for new atoms to open the double bond and react there than to remove the hydrogen already attached, and then bond to it, which would be a substitution reaction.

The Reaction Between Symmetrical Alkenes and Bromine

Alkenes are more unstable than alkanes, because alkenes have double bonds, which include a pi -bond, and pi -bonds are weaker than sigma -bonds. Alkenes have some strong bonds and some weak bonds, while alkanes only have strong bonds. Why is ethene and bromine an addition reaction? Apr 9, Explanation: Ethene and bromine are an addition reaction because ethene is an alkene - it has a double bond. It forms dibromoethane, which is a halogenoalkane.

why is the reaction of ethene with bromine called an addition reaction

Related questions Question a. Why are organic compounds important? How are compounds in organic chemistry named? What is the general formula of a carboxylic acid? What is a carboxyl group? What is an alkane? What is the formula of the ethyl group? What is a functional group in organic chemistry? See all questions in Definition of 'Chemistry' and 'Organic'. Impact of this question views around the world.

You can reuse this answer Creative Commons License.This page gives you the facts and a simple, uncluttered mechanism for the free radical substitution reaction between methane and bromine. If you want the mechanism explained to you in detail, there is a link at the bottom of the page. This reaction between methane and bromine happens in the presence of ultraviolet light - typically sunlight. This is a good example of a photochemical reaction - a reaction brought about by light.

It is better to use the term "photochemical" and keep the word "catalysis" for reactions speeded up by actual substances rather than light. One of the hydrogen atoms in the methane has been replaced by a bromine atom, so this is a substitution reaction. However, the reaction doesn't stop there, and all the hydrogens in the methane can in turn be replaced by bromine atoms.

Multiple substitution is dealt with on a separate page, and you will find a link to that at the bottom of this page. Check your syllabus at this point. If your syllabus wants you to know about the free radical substitution reaction between methane and chlorine as well as this one, don't waste time trying to learn both mechanisms.

The two mechanisms are identical. You just need to learn one of them. If you are asked for the other one, all you need to do is to write brominesay, instead of chlorine.

Why is a reaction between ethene and bromine considered as an addition reaction?

In writing the bromine mechanisms on these pages, that's exactly what I've done! If you read both chlorine and bromine versions, you'll find them boringly repetitive!

why is the reaction of ethene with bromine called an addition reaction

The mechanism involves a chain reaction. During a chain reaction, for every reactive species you start off with, a new one is generated at the end - and this keeps the process going.

It covers molecules, ions, atoms, or in this case free radicals. The over-all process is known as free radical substitution, or as a free radical chain reaction.

Use the BACK button on your browser to return quickly to this page. Chain initiation The chain is initiated started by UV light breaking a bromine molecule into free radicals.

Chain propagation reactions These are the reactions which keep the chain going. Chain termination reactions These are reactions which remove free radicals from the system without replacing them by new ones. Look at why side reactions happen in this reaction. The facts This reaction between methane and bromine happens in the presence of ultraviolet light - typically sunlight.This page guides you through the mechanism for the electrophilic addition of bromine to symmetrical alkenes like ethene or cyclohexene.

Unsymmetrical alkenes are covered separately, and you will find a link at the bottom of the page. The structure of ethene is shown in the diagram on the right.

The pi bond is an orbital above and below the plane of the rest of the molecule, and relatively exposed to things around it. How, then, can bromine be an electrophile? Equally, if you aren't sure about terms like electrophilethen it really would be a good idea to read the page What is electrophilic addition? In fact, bromine is a very polarisable molecule - in other words, the electrons in the bond are very easily pushed to one end or the other.

As the bromine molecule approaches the ethene, the electrons in the pi bond tend to repel the electrons in the bromine-bromine bond, leaving the nearer bromine slightly positive and the further one slightly negative. The bromine molecule therefore acquires an induced dipole which is automatically lined up the right way round for a successful attack on the ethene.

What is an "induced dipole"?

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Where it does already exist - as, for example, in HBr - it is called a permanent dipole. If you've come into this web site from a search engine directly to this page, read the notes on the introductory page to this reaction before you go any further. In the process, the electrons in the Br-Br bond are repelled down until they are entirely on the bottom bromine atom, producing a bromide ion. If you aren't sure about the use of curly arrows in mechanisms, you must follow this link before you go on.

The ion with a positive charge on the carbon atom is called a carbocation or carbonium ion. Why is there a positive charge on the carbon atom?

The pi bond was originally made up of an electron from each of the carbon atoms. Both of those electrons have been used to make a new bond to the bromine.

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That leaves the right-hand carbon an electron short - hence positively charged. In the second stage of the mechanism, the lone pair of electrons on the bromide ion is strongly attracted to the positive carbon and moves towards it until a bond is formed. There is a real risk of getting confused. If your examiners are happy to accept the simple version, there's no point in making life difficult for yourself.

The reaction starts off just the same as in the simplified version, with the pi bond electrons moving down towards the slightly positive bromine atom. But this time, the top bromine atom becomes attached to both carbon atoms, with the positive charge being found on the bromine rather than on one of the carbons.

A bromonium ion is formed.

why is the reaction of ethene with bromine called an addition reaction?

The bromonium ion is then attacked from the back by a bromide ion formed in a nearby reaction. It can't be attacked by its original bromide ion because the bromonium ion is completely cluttered up with a positive bromine on that side. It doesn't matter which of the carbon atoms the bromide ion attacks - the end result would be just the same. In the process, the electrons in the bromine-bromine bond are repelled until they are entirely on the right-hand bromine atom, producing a bromide ion.Ethene ethylene has the molecular formula C 2 H 4.

Ethene ethylene belongs to the alkene homologous series. Please do not block ads on this website. Ethene ethylene undergoes complete combustion in excess oxygen to produce carbon dioxide and water. Play the game now! Ethene, ethylene, is an important chemical in the production of other chemicals. Some of the uses of ethene ethylene in industry are given in the table below:.

Take the test now! The cracking process typically involves endothermic equilibrium reactions such as:. To maximize the rate of the cracking reactions:. To maximize the yield of ethene, by Le Chetalier's Principle :.

why is the reaction of ethene with bromine called an addition reaction?

So increasing the temperature speeds up the rate of the reaction and increases the yield of ethene. However, a decrease in pressure would slow down the rate of the reaction. For this reason the pressure is kept at or below atmospheric pressure. Equilibrium is therefore never actually achieved this is not a closed system. Do you know this? Do you understand this?

Can you apply this? Take the exam now! Addition of Hydrogen bromide. Addition of Hydrogen chloride. Production of Polythene polyethylene. Production of Styrene styrene can be polymerised to form polystyrene. Production of chloroethane chloroethane is used to manufacture tetraethyl lead tetraethyl lead is the lead additive in leaded petrol.

Ethene is also used as a plant hormone to control the ripening and colour development of fruit.This page gives you the facts and a simple, uncluttered mechanism for the electrophilic addition reactions between bromine and the other halogens and alkenes like ethene and cyclohexene.

If you want the mechanisms explained to you in detail, there is a link at the bottom of the page. Alkenes react in the cold with pure liquid bromine, or with a solution of bromine in an organic solvent like tetrachloromethane. The double bond breaks, and a bromine atom becomes attached to each carbon.

The bromine loses its original red-brown colour to give a colourless liquid. In the case of the reaction with ethene, 1,2-dibromoethane is formed. This decolourisation of bromine is often used as a test for a carbon-carbon double bond. If an aqueous solution of bromine is used "bromine water"you get a mixture of products.

The presence of the water complicates the mechanism beyond what is required by current UK A level or equivalent syllabuses. The other halogens, apart from fluorine, behave similarly. Fluorine reacts explosively with all hydrocarbons - including alkenes - to give carbon and hydrogen fluoride.

If you are interested in the reaction with, say, chlorine, all you have to do is to replace Br by Cl in all the equations on this page.

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One version is simplified to bring it into line with the other alkene electrophilic addition mechanisms.

You will probably find that your examiners will accept this one, but you must find out to be sure. You almost certainly won't be able to tell this from your syllabus. You need to refer to recent mark schemes, or to any support material that your examiners provide.

If you still aren't sure, contact your examiners direct. If you are working towards a UK-based exam, you can find out how to do this by using the link to your Board's web site on the syllabuses page. The person you need to contact will probably have the title Subject Officer for Chemistry or something similar. Ask whether they want the mechanism for the reaction between bromine and alkenes which proceeds via a carbocation or via a bromonium ion intermediate.

The bromine is a very "polarisable" molecule and the approaching pi bond in the ethene induces a dipole in the bromine molecule. If you draw this mechanism in an exam, write the words "induced dipole" next to the bromine molecule - to show that you understand what's going on.

There is a real risk of getting confused. If your examiners are happy to accept the simple version, there's no point in making life difficult for yourself. In the first stage of the reaction, one of the bromine atoms becomes attached to both carbon atoms, with the positive charge being found on the bromine atom. A bromonium ion is formed.

Cyclohexene reacts with bromine in the same way and under the same conditions as any other alkene.

why is the reaction of ethene with bromine called an addition reaction

Again, there are two versions of this mechanism in common use, and you must know which your examiners will accept. Again, the bromine is polarised by the approaching pi bond in the cyclohexene. Don't forget to write the words "induced dipole" next to the bromine molecule. Look at the same reactions involving unsymmetrical alkenes. The electrophilic addition of bromine to ethene The facts Alkenes react in the cold with pure liquid bromine, or with a solution of bromine in an organic solvent like tetrachloromethane.

The mechanism for the reaction between ethene and bromine The reaction is an example of electrophilic addition. Bromine as an electrophile The bromine is a very "polarisable" molecule and the approaching pi bond in the ethene induces a dipole in the bromine molecule. The simplified version of the mechanism.


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