hello this is Dr Henna aseel and this is a part of the organic chemistry for the A2 chemistry syllabus this is on aldehydes and ketones so let us talk about uh aldehydes and ketones these are carbonyl compounds if we're trying to name them all the names of aldehydes end with Al like the one that has one Corbin that's methanol ethanol propanal Butana the functional group of course is always at the end at the end it is a c single Bond H double bond o so these are ketones end with own proper non [Music] butthenon two pentanone if the C double bond o is on carbon number two c double Bondo and carbon number three that's three pencil and so on so the functional group of a ketone is in the middle of the chain it is made up of a c double bond o that is bonded to two groups which we call two alkyl groups or master or ethylenson aldehydes and ketones if we look at the structure of an aldehyde and the Ketone aldehyde we said has a Cho at the end Ketone has a CW Bond o in the middle so both of them have the C double bond o which is a polar part of the molecule and this causes the aldehydes and ketones to have higher boiling point than the corresponding alkanes remember that these would have dipole-dipole interactions in the aldehyde and ketones so this will have higher boiling point than an alkene that only has the weak Van Der waals forces between each month also aldehydes and ketones will not form hydrogen bonds with each other so an aldehyde cannot form hydrogen bond with another molecule of its own ketones will not form intermolecular hydrogen bonds so their boiling point compared to an alcohol would be lower remember that alcohols have oh and they can form hydrogen bonds between each other between their molecules so uh the boiling point of an alcohol would be higher than that of an aldehyde and Ketone because of the intermolecular hydrogen bond but if we try to dissolve them in water aldehydes and ketones will dissolve in water since the polar sea double bond oh will form hydrogen bond with what it cannot form hydrogen bond with another molecule like itself but it will form hydrogen bonding with water so it will dissolve in what so let's look at this question ethanol and propane what is ethanol ethanol is the aldehyde that has two carbons propane is the alkene with three core now he's saying they both have the same molecular mass but ethanol has a much higher boiling temperature we said aldehydes will have higher boiling points than an alkane why because it has what it doesn't form hydrogen bonds with itself but it will form permanent dipole-dipole interactions Now ethanol we said is fully miscible in water again why does it dissolve in water because it has hydrogen bonds with what or it can form hydrogen bonds with what propane what is propanone again that's propanol has a much higher boiling temperature than be within now we said why is it that a ketone will have higher boiling point than an alkane again because propanone has permanent dipole dipole interactions between its molecules while butane will have only the weak Van Der waals forces so propanone has higher boiling points remember propanone does not form hydrogen bond between its molecules to B is wrong uh propanone does not have a it's not because it has stronger London forces between its molecules and it's not because the carbon oxygen double bond in propanone is very strong that has nothing to do with boiling point another question some of the physical properties of aldehydes and ketones can be explained by the fact that they what never form hydrogen bonds no we don't say they never form hydrogen bonds we said they form hydrogen bonds with water but not with each other okay they form hydrogen bonds in the liquid state but not in the aqueous stage remember liquid state means when I melt them no they don't form hydrogen bonds with each other they form hydrogen bonds with water so we said they form hydrogen bonds in aqueous Solutions but not in liquid state that means not with each other okay tests for aldehydes and ketones remember if I want to distinguish an aldehyde or a ketone from anything else I use two for dinitrophenylhydrazine so both aldehydes and ketones will react with two for the nitrophenol hydrazine to give an orange yellow precipice both aldehydes and ketones form an orange yellow precipitate with two for the nitrophenol hydrazine so I use this test to distinguish between aldehydes and ketones and something else like alcohols or alkenes and things like that then to distinguish between aldehydes and ketones we use tolerance reagent so this is one of them because only aldehydes react with tolerance reagent tolerance reagent is actually a sort of complex between silver and ammonia when you reacted with aldehydes it gives silver and the silver precipitates on the sides of the test tube so we see this is a silver mirror and remember only aldehydes will react with solon's reagent to form a silver Mero again only aldehydes react with Benedict's solution you remember what is Benedict solution all felling solution which is actually a copper sulfate solution when the aldehydes react with copper sulfate which is blue it turns it to Brick red precipitate this is because aldehydes will reduce the copper II to Copper one so it changes copper II sulfate which is blue to Copper one oxide which is a brick red crisis okay let's take a look at this question an unknown aldehyde may be identified by measuring the melting temperature of the precipitate formed in its reaction with what so aldehydes will react with which of these to give our precipitate remember we said it get it gives a precipitate width to for the nitrophenol hydrazine it doesn't give a precipitate with failing with tolerance it gives a silver mirror and remember potassium dichromate and sulfuric acid this is a an oxidizing agent and it will oxidize the aldehyde to an acid so it doesn't give a precipit again this question says remember ethanol is an aldehyde is warmed with either failing solution or Benedict solution a red precipitated spoon what are the red precipitate and the organic product we said when you react an aldehyde with falling or Benedict which is copper sulfate it will reduce the copper 2 to what to form copper one oxide and the actually the organic product formed would be the sodium salts of the aldehydes of or actually it will be the sodium salt of an acid food so this is sodium ethano weight which test is used to distinguish between aldehydes and ketones again which test aldehydes will react and not ketones remember it is failing or Benedict solution which will give a break red precipitate with aldehydes only which test results in an orange yellow precipitate with this what is this can you see that this is propane so it's a ketone so which one gives orange yellow precipitate with a ketone we said both aldehydes and ketones react with two for the nitrophenyl hydrazine this Ketone will not react with fairlinks or Benedicts uh it will not react actually with sodium carbonate we will talk about the reaction of iodine and alkaline in a minute but remember that both aldehydes and ketones will give orange yellow precipitate with two for dinitrophenol hydroxine how many structural isomers with molecular formula this react with tolerance rage first of all we said which ones we react with tolerance reagent it has to be an aldehyde so he's asking how many aldehydes will have this formula so let's start drawing the different aldehydes with five carbons this is one aldehyde with white Corbin this is another aldehyde if it is four and it has a branch this is another aldehyde of the branch is on a different Corbin this is another aldehyde when you have the three corbins and then two vessel groups as branches so this gives us four different isomers that can react with tolerance because they are all at the heights this question refers to the following molecules all of which have a carbonyl group and he says a brick red precipitate is formed on warming uh blue Benedicts or fairlings with what again Benedicts or failings we react with aldehyde so he's basically asking which of these are aldehydes remember that these two are aldehydes the others are actually ketones so only W and X will react with Benedict's old family again butanone can be distinguished from butanoic Acid by the addition of what this is a ketone and I'm trying to uh distinguish it from an acid so which one will this react with remember we said ketones will react with two for the nitrophenyl hydrazine they don't react with Fanning or with tollens so this would be the one that will distinguish the butanoon the Ketone from there which correctly shows the reactions of ethanol this is ethanol propanone remember keep all of these in mind what is he talking about so he's saying which of these we react with tolerance remember ethanal is an aldehyde so it will react with stones which of them will react with two for the nitrofarin hydrazine well both aldehydes and Ketone so both ethanol and propanone will react with two food and nitrophthanol hydrazine again a compound x with molecular formula this gave an orange precipitate with two for the nitrophenol hydrazine what does that tell you if it gives an orange precipitate with two for the nitrofen and hydrazine that means it is either aldehyde or King then it also gave a silver mirror with tolerance that means it's what it's an aldehyde so which of these could not be X so the question is which of these is not an aldehyde so that would be D the others are all aldehydes sucrose can be hydrolyzed by warming with dilute hydrochloric acid remember that sucrose is actually an aldehyde because it has the Cho group at the top State what change you would expect to see when glucose is boiled with Benedicts or pharynx so this is actually an aldehyde I'm reacting it with Benedict or failings it will reduce the C2 to C1 so the blue copper sulfate solution turns into the brick red precipitate which is copper one he's asking you to explain the chemistry involved that means you need to mention that the aldehyde is a reducing agent it uses the copper II in Benedict or felling to Copper one that's why you get a brick red prism okay how do we prepare aldehydes and ketones well one method of getting an aldehydrate Ketone is oxidation of alcohol remember that if I have an alcohol so let's say I have a primary alcohol if I add acidified potassium dichromate or acidified potassium manganese it the first thing is the primary alcohol is oxidized to an aldehyde if I continue to oxidize it it further oxidizes to acid so this is one method of getting an aldehyde so remember oxidation of a primary alcohol gives alcohol but if I'm doing the same to a secondary alcohol we said in that case I get a kit again we're doing alcohols with an oxidizing agent acidified potassium dichromate or acidified potassium manganese primary alcohols give aldehydes secondary alcohols give Heat or I can go get the aldehyde by reduction of an acid so if I have an acid I can react it with lithium aluminum hydride in dry it so the agent is lithium aluminum hydride in dry ether will change the acid to an aldehyde and further reduction will give an alcohol this aldehyde is then obtained by reduction of an acid and the reagent is lithium aluminum hydride in dry ether okay let's take a look at this question it says ethanol may be prepared by which of these okay let's take a look at the choices the first one says heating ethanoic acid with lithium aluminum hydride and dry ether this will actually give ethanol but it will continue to give ethanol at the end so this will actually give an alcoholic now if I say refluxing a mixture of bromoethine and sodium hydroxide well bromoethane and sodium hydroxide would give me the alcohol not the aldehyde refluxing a mixture of ethanol with acidified potassium dichromate remember we said we can oxidize our primary alcohol to an aldehyde but if you heat it under reflux it goes on to form an acid it does not stop at the aldehyde if we say distilling from a mixture of ethanol with acidified potassium dichromate that is when we get the aldehyde so as it forms I distill it out so it does not continue until it forms so that is my truth okay reactions of aldehydes and ketones so if I have an aldehyde or a ketone if I put a reducing agent like lithium aluminum hydride in dry ether it will reduce the aldehyde or the Ketone to form an alcohol so this is actually how we get an alcohol from an aldehyde and Ketone remember this is lithium aluminum hydride in dry ether or I could add hydrogen cyanide so an aldehyde or a ketone would react with hydrogen cyanide hydrogen cyanide is obtained by sodium cyanide in presence of an acid so this is uh something that will give a CN and an o h on that carbon so it's called a cyanohydram I can go on to hydrolyze this cyanohydrin and it will continue to give an acid so this is actually a method of doing what this is a method of adding a new carbon on the Chain so this added an extra Carbon on the Chain I can also continue to um react the product with concentrated sulfuric acid at high temperature like 180 degrees Celsius and I end up with the alkene that has an extra carbon from what I started with okay what is the mechanism of the addition at the carbonyl the nucleophile attacks at the Corbin the electrons move to the oxygen so I get an O minus and this o minus reacts with the acid because this is in presence of acid and it gives me the cyano hydro okay did you notice that mechanism let's take a look at this question this question is about reaction of cyanide ions with a ketone and a student wrote this mechanism what is the error in this mechanism of course the cyanide will attack the carbonyl that is correct but then what is he doing he's saying the h plus will attack the O minus no it is the O minus that will attack the h plus so the direction of the curly Arrow from the hydrogen ion is the wrong part of this mechanism Which diagram shows the first step of the mechanism of nucleophilic addition of hydrogen cyanide to propanone in presence of potassium cyanide okay so we said the cyanide should attack the carbonyl and the double bond of the carbonyl electrons will go to the oxygen to form an O minus so which of these is the correct one okay can you see that a is the correct one what's wrong with the others be uh he has an arrow going from the double bond to the Corbin that's trunk it has to go from double bond to the oxygen now what's wrong with c c has the wrong uh partial charges on the carbon the carbon should have a partial positive and the alternate partial negative so C is wrong and d uh what's wrong with d this out the arrow is going from the carbon to the cyanide that's wrong okay so reactions of the carbonyls with aqueous iodine alkaline aqueous iodine this is called the iodiform test and this is a test to show the presence of a certain group if I have a ketone that has ch3co I can show that it has this group because it will react with iodine in presence of sodium hydroxide aqueous so this is alkaline aqueous iodine and it forms a yellow precipitate can you see the yellow precipitate so formation of a yellow precipitate in The iodoform Test shows that I have my Ketone I have a group which is ch3co so let's look at this question a carbonyl compound with molecular formula this reacted with iodine in alkaline solution to give a pale yellow preceptor that means that it has the ch3co group now which one has ch3co that is this one so this is the one that will give pale yellow precipitate in the iudiform test the others don't have this group reacts with iodine in presence of sodium hydroxide the precipitate form has what formula remember when we have propanoon propane ch3c och3 so it does have the ch3co group so it will form a yellow precipitate with the aqueous um iodine aqueous alkaline iodine now the precipitate has what formula we said this is the formula of the precipitate that is food this question refers to these compounds and he says a pale yellow precipitate is formed when iodine in Alkali reacts with which of these again iodine with Alkali will give a yellow precipitate if the compound has what ch3co so which compounds have ch3co that's y and z questions about nucleophilic addition of hydrogen cyanide to butano now he's saying that the cyanide attacks the Corbin and the dog the electrons go to the oxygen that is correct so what is the intermediate that is formed which one is correct he said this one is correct in which the cyanide attacks so the O noun has an o minus which statement about the mixture of organic compounds formed is not correct so which of these is not correct um he's talking about this reaction of course and he's saying the organic products of this reaction which statement is not correct if you look at this one we're saying he's saying it we rotate the plane of polarized light no we said when the nucleophile attacks on the carbonyl it can attack either from the front or from the back and that means a racinic mixture is formed under a Civic mixture will not have any effect on the plane of polarized blood an organic compound gives a pla pale yellow precipitate when warmed with iodine sodium hydroxide what does that mean it has ch3co it also gives steamy fumes when tested with phosphorus pentachloride you remember which group will give stimi fumes with pcl5 well that is an alcohol so what we're looking for is something that has both a ch3co and an alcohol so it is this yes okay thank you for listening that was about aldehydes and ketones and in the next videos we will continue talking about organic chemistry thank you