[Music] hello and welcome to this video on Halo alanes This is for OCR um my name is Chris Harris and I'm from allery tutors.com and basically the whole point of this video is to basically give you a quick overview of the Halo Alan's topic um great for things that revision um you can use these slides as well you can uh get a hold of them use them print them off and and have them on your smartphone tablet um computer PC whatever you use um you can purchase them if you just click on the link in the description box and you can get a hold of them um get a hold of them there okay like I say these are specifically for OCA and they match the specification points as you can see listed on here so it's all good if you are um studying this syllabus okay so let's start so we're going to start with naming halogeno alkanes we' got to be able to name them first before we know a little bit more about them so halogeno alkanes these are alkanes with one or more hogen attached to it um so you get obviously loads of different parts so when you're naming them the first thing you need to do is find the longest carbon chain just like with any nomenclature of organic compounds you need to find the longest carbon chain and this will form the last part of the name as you'll see in a minute then the names and positions of the halogens and the molecules come first so um they come as what we call a prefix and we prefix them with fluo chloro bromo or iodo depending on what hogen you're using and obviously the number on the carbon chain that it sits at we need to prefix that as well so it might be two iodo or three bromo or whatever whatever the molecule is and there must be an alphabetical order I think a lot of people forget this um so you've got to have obviously bromo before chloro um irrespective of the number that they sit on so it's not numerical it's alphabetical so make sure you're doing it in that order um and also if you have more than one type of H hallogen as well um you prefix with d try or Tetra um so obviously DY for two try for three and Tetra for four so let's have a look at some examples so you can see here we've got this one here uh got three flines attached to one carbon so because this is just uh one carbon that's methy and three Florin we got three of them so it's Tri fluo okay so this one should be Tri fluo methane simple as that okay let's a look at another one uh this one here a bit longer three carbons obviously this makes it prop chlorine sitting on the second carbon so that's going to be two chloropropane and another example this one's a bit more of a mixed bag I've really G adventurous here so I've got um two chlorines one bromine one iodine on an e molecule so naming it as you can see it's one bromo cuz we got the bromine on the first carbon One One D chloro because we've got two chlorines on the first carbon uh and then two iodo ethane so because the iodine sitting on the second carbon but notice that it's done in alphabetical order so it's bromo chloro iodo okay so make sure you do it in alphabetical okay so let's have a look at Bond polarity and nucleophiles because all halogeno alanes or haloalkanes um as they're also known as uh they have a polar bond because they have a hallogen attached to them um and they are attacked by nucleophiles so the idea is is that these halogens are electronegative and they pull electrons towards themselves in a calent bond um and obviously this leads to the polar bond and you can see the Delta negative here and the Delta positive here which is left on the carbon now this is going to leave it open to attack by nucleophiles so which is um which is obviously going to be the crooks of most the reactions for Halo alkanes so a nucleophile is just something that is an electron pair donor so it has a lone pair of electrons attached to it so you need to know these specific examples uh ammonia hydroxide ions so ammonia is there look NH3 hydroxide ions o minus cide I CN minus and water uh which is H2O I've just drawn that in a different way just to show consistency in terms of the placement of the lone pair of electrons okay so these are actually weak nucleophiles okay so cly AR show the movement of electron Pairs and you can see here this is represented by a nucleophile and the nucleophile has a lone pair of electrons there and basically what these do is they move from the lone pair of electrons to the Delta positive carbon on the Halo alkane because these have a lone pair they've attracted to the Delta positive on here and this is basically the start of your nucleophilic reactions to do with halogeno alanes or Halo alanes as you'll see later on okay so let's have a look at a specific example so we've got hogen alanes they react with hydroxide ions uh and these undergo uh these react via a nucleophilic substitution reaction okay so the conditions for this is warm aquous sodium hydroxide uh the source uh basically this gives you the source of O minus ions and it's carried out under reflux so you can see here here's our setup here we've got a chloroethane here one chloroethane uh and we've got a hydroxide iion here now what will happen is this nucleophile here will attack this Delta positive carbon which is on here always show you partial charges as well uh and will replace the hallogen so it'll kick this hallogen off um and we call this a substitute ution reaction because we're substituting the hydro the chloride the chlorine on the Halo alane and the hydroxide so here we go curar look so must go from the area where there's electrons to the D positive carbon and because this is forming a bond with a carbon this bond has to break to um to basically allow this to bond to that carbon so that's exactly what we're going to get um and we're going to call this heterolytically okay so hetro meaning different so because all or both electrons in this Bond are moving on to one atom we call it a hrotic um fish which is the breaking of a bond both electrons move to the hallogen and a new bond is formed between the O minus ion and the carbon so there it is okay so you can see this mechanism stting form and obviously now we just need to write our product our product is an alcohol because we've swapped the hogen for the O there's the alcohol there this is a primary alcohol in this case um we've got a chloride which is over there the overall reaction for this well pretty straightforward rxx normally symbolizes a hallogen you might see that quite a few times R is an alkal group and so like C3 so you can see here that we've got our halo alane react with sodium hydroxide forms our alcohol and sodium helide which is your salt so that's your overall reaction okay let's have a look at the reaction with water okay CU they will react with water though water is not a great nucleophile it's quite weak but um nonetheless it will still react so uh hogen ales react with water in nucleophilic substitution as well again to get this reaction going we need to heat it um because it is pretty slow in cold water so heating it up just helps this reaction to go so we're going to heat it with water uh and water's a weak nucleophile like I say the reaction's slower okay than using a hydroxide and an alcohol is produced so you can see here um we've got our water no mechanism required here um there's your water it's reacting with your Halo alane which is here and that's going to produce your alcohol plus H+ plus BR minus so uh we're still producing an alcohol but instead of obviously having a salt being formed we're going to form a hydrogen helide being produced over here on the side so it's just a slightly different reaction but the mechanism essentially is the same okay so Halo alane reactivity okay so we need to know how these things react Halo they become more reactive as we go down the group and they're hydrolized the fastest we'll look at hydrolized in a minute so what determines the reactivity so the bond strength and the bond enthropy determines the reactivity it's not the bond polarity so we're not looking at the polarity in this case I think it's a quite a misconception that some people think it is the polarity that determines um how reactive it is but it's not it's the strength of the bond so let's have a look so we got this table of bond enies um of different hogen carbon hogen bonds okay the carbon iodine bond this one here is the lowest bond enthropy is the easiest one to break this means any reactions with CI will be the most reactive and hence will be hydrolized the fastest okay so these ones here which is CI this one breaks the easiest you see the CF is the strongest at the top there um and here's the evidence so we're going to react a Halo alkan with aquous silver nitrate and you'll get these different results so the first thing we do is pour our chlorine chloro alkan into um uh well all the all your Halo alanes actually H into three separate test tubes you chloro Alcan bromo alkan iodo alkan uh and then we're going to add silver nitrate solution and ethanol which is the solvent into each tube so we're going to add each one of these uh into the tube and basically it's like a Time an exercise so the iodide gets first prize uh this one the precipitate forms first this is because the bond is the weakest so um it means it's been um it's been broken uh easily and therefore the precipitate is formed first so that one gets first prize and in second place it's the bromine um it's got the next strongest bond it takes a little bit longer uh to break these bonds so it comes in second and you form silver bromide that's the name of the uh the precipitate that we're getting it's a cream precipitate and there's the by the way there's the ions that's formed so it's the silver iron in silver nitrate react with a bromide iron this is obviously cleaved from the um uh from the um Halo alkane so that's where that comes from and obviously if that's broken relatively easily you'll get plenty of this and so you get this quicker and that's your solid precipitate and in third place is the chloride iron gets the gets The Wooden Spoon so um the so white precipitate forms last the chloride iron uh the chlorine carbon bond is stronger out of the three um so therefore it takes the longest to form the precipitate um which is silver chloride which is the white precipitate okay um so yeah the um hydrolized is basically the breaking of this Bond as you can see obviously in all of these um uh in all of these examples here okay okay so cfc's obviously Halo alkanes um are were used quite extensively um especially in Britain anyway um in the past um for things like refrigerants however there are problems with them and we're just going to learn a little bit more about obviously cfc's and what their roles were and the kind of things that we use today so CFCs are basically chloro fluo carbons okay and they break down ozone which is o03 in the atmosphere so these molecules um have had all their hydrogens replaced by chlorine and Florine okay so um they're basically just like like an alkane but you've just taken all the hydrogen away and you've replaced them with chlorine fluin so they're stable molecules but they are broken down by UV um and that especially happens higher up in the atmosphere so your CCL bonds here's a here's an example of a CFC the CCL bonds are broken down by UV radiation you can see it here there it is okay so it comes in breaks down the um the breaks the bond between the carbon and the chlorine and what you get is radicals you get radicals that are formed and what these do and fortunately these catalyze the breakdown of ozone and these CCL bonds are broken the easiest as we've seen in the um in the table below uh table before the CCL bond is the weakest out of all of them so this one's going to be broken down the easiest you have the lowest Bond enthropy your CF bond is less likely to be broken because the bond is stronger in comparison to the CCL Bond so that's why we break down this so again bringing that Bond enthropy okay so let's see how they destroy ozone then so what they do is they break down to form chlorine radicals and these cataliz the breakdown of ozone okay so we're going to start with initiation so initiation remember is the um is basically the formation of radicals uh and we form them from UV radiation so again we're going to use a CFC this time so the CFC is here we got the carbon chlorine bond UV comes in okay and we produce two radicals and what these will do is these will react with ozone molecules so here it is here so we've got ccl3f plus the H mu is just this is just radiation um this is like UV it just symbolize it using radiation and we form our two radicals you can see the chlorine has been um the chlorine carbon bond has been broken and so we've got a chlorine radical and the um rest of the CFC U radical here then we got propagation and basically it's the CL Dot from here reacts with the ozone O3 to form clo dot intermediate and O2 and then the clo dot that was formed in the first step reacts with more ozone and it makes oxygen and more CL Dot and then this CL dot is reformed it proof that it's a catalyst and then this CL dot can actually go back and react again so I'll show you as an example so the first propagation step your chlorine radical that was taken at the start here reacts with ozone in the atmosphere to form oxygen and this clo dot intermediate the reason why it's an intermediate is because this radical is used as a reactant in the Second Step which is here there it is CLO dot plus ozone will form two lots of Oxygen Plus CL dot um and you can see here obviously that's the radical that's been formed in this the product in the Second Step must be the reactant in the first step so it's reformed again so that's proof that chlorine CL do is a radical is a catalyst as well and radicals it's both okay so um termination okay so this is where we get two radicals and we Collide them together so for example we can form chlorine again two CL dot radicals can um Can Collide to form chlorine and there's the example there so CL dot plus CL dot will form cl2 now the overall equation then is if you look on there we've circled them you can see we've got two lots of ozone are basically being broken down into three molecules of oxygen and so I've circled it in these two equations here and written the overall thing and the uh overall reaction your CL dot is a catalyst because it's been used up here but then crucially it's been reformed here so CL dot is the catalyst okay some other radicals that destroy ozone you just need to have an awareness of these really um nitrogen oxides um these are formed from vehicle emissions and thunderstorms as well these can also destroy ozone so you got to be you got to be careful with these molecules as well again what we're going to do is we're turning nitrogen dioxide which is here into um your no dot radical and an oxygen atom okay which is here again we're using UV radiation and the no radical this is the bit we're really focusing on here and this reacts with the ozone um just um just like the chlorine radical did in the previous slide that we looked at so what we're going to do is we're going to use r as the radical okay as the radical formed in the in the initiation step and it just helps you to tag it just a little bit easier because there's a lot of oxygen floating around here so here's the radical okay arpha radical reacts with the ozone so this is the radical produced from here okay reacts with the ozone and what it does is it forms oxygen and your radical bonded to oxygen so it's a bit like clo dot again it's very similar to the in fact it is the same as the reaction that we're doing before so this could be any radical so the exam world could could pick up any radical they want and then basically it's the radical oxide uh from the um from this step is dragged down and used in the Second Step reacts with oxygen atom uh and that will form oxygen O2 which is oxygen molecule plus your radical Ral is reformed again this is acting as a catalyst because we have the radical here and we got the radical in the reactant and radical in the product so it's acting as a catalyst so you can see here this is just showing you a generic overview of um of obviously the oxygen um this oxygen here um this is appeared because when UV breaks down um oxygen which is obviously around um this oxygen has come from here so that's how that's where this oxygen has come from because the UV has actually created it in the atmosphere so remember you has got a lot of energy and it will react with a lot of things like this so that's where that's come from okay so make sure you know um about obviously how these um how the nitrogen dioxide can be used as a as a me as a vehicle as opposed to to break down ozone in the upper atmosphere okay so obviously cfc's you can see as you can see they've been quite um dangerous um they damage the ozone layer um and obviously there are laws now restricting the use of it so they are banned effectively in the United Kingdom they are anyway so cfc's are really stable they're unreactive they're non-toxic chemicals um and they were used as fridges or used in fridges sorry as refrigerants um and propellants and deodorant sprays um so they were used quite widely um um maybe 20 30 years ago um it was quite common for them to see them in these fridges um but however it was demonstrated later on by scientists that CFCs were damaging the ozone layer um and actually the advant ages of these brilliant chemicals at the time um and they they were really cheap you could put them in fridges and it allowed Refrigeration Etc obviously their risks though which they didn't know at the time till after the use of these things um obviously damaged the ozone layer and now they're looking for other methods or other Alternatives because it isn't good when you've got an ozone layer remember the ozone layer actually the reason why it's there is it absorbs some of the harmful UV radiation that comes from the sun it blocks some of that radiation out and stops it from getting uh down to living organisms on the earth um and obviously um some some animals and plants obviously are affected in particular animals are affected by strong UV and obviously um so for example in humans you can get things like skin cancer um malignant melanoma um and obviously we don't want we don't want any of that if we can help it if we can try and reduce it um and obviously restricting uses of cfc's prevents the damage to the ozone which obviously blocks the harmful UV radiation okay so let's look at some Alternatives in so in 1989 okay so you know short while ago uh the Montreal protocol uh International treaty set out to ban the use of cfc's in most products by the year 2000 so it was like this Millennium Project for them okay so work was underway to come up with alternatives to cfc's um cfc's could still be used for research and fire extinguishers so they they do still do have uses um but there's a real drive to to replace them um there was a an international um um organized Committee of leaders global leaders to try and uh tackle these problems here so today um obviously we use temporary Alternatives that are a lot safer we use something called hfc's or hydrocarbons um so basically they don't have chlorine in and that was the main culprit to breaking down um CFC so um it's gone some way uh to to effectively reduce the risk to the ozone layer so hfc's and hcfcs are very potent greenhouse gases though so just as soon as you solve one problem you've got another okay so which is much worse than carbon dioxide so again it's not really ideal so even hydrocarbons which are used in fridges today um they're greenhouse gases as well so again it's just about managing the uh waste products that we've got and using and managing them effectively like I say we use pump sprays and inert gases such as nitrogen as propellent now so there are lot saer night which is obviously a natural gas in the atmosphere um industrial fridges and freezers now use ammonia um as the refrigerant so um ammonia is quite is relatively stable it's not as stable as cfc's um but it's nowhere near as damaging as um to obviously it won't affect the ozone layer so it's a bit easier to use and we can dispose of it um better um obviously today and who knows technology might improve even further it might come up with a completely different chemical that might be even better than monia um obviously the proof is that there is scientific evidence to suggest now the ozone layer is closing back up again which is good news um it is becoming slowly smaller it is blocking back up again so clearly the effect of the Montreal protocol um and the the global efforts of reducing cfc's is obviously working because the OZO layer is closing back up again and that's pretty much it that's an overview of Halo alkanes it's a nice topic actually there's quite a bit of um um real chemistry in there and applied chemistry um please support this channel it's really uh appreciate that by just subscribing um and sharing it um if you just click on the little circle in the middle you can subscribe to the channel um also just reminder that these PowerPoints can be purchased if you just click on the link in the description box below and you can get a hold of them and use them as your revision notes but um that's it bye-bye