Properties of Anomers - Mutarotation

Video thumbnail (Frame 0) Video thumbnail (Frame 11591) Video thumbnail (Frame 23007) Video thumbnail (Frame 34423) Video thumbnail (Frame 45839) Video thumbnail (Frame 54734) Video thumbnail (Frame 63447) Video thumbnail (Frame 68225) Video thumbnail (Frame 69370) Video thumbnail (Frame 74698)
Video in TIB AV-Portal: Properties of Anomers - Mutarotation

Formal Metadata

Title
Properties of Anomers - Mutarotation
Title of Series
Part Number
25
Number of Parts
27
Author
License
CC Attribution - ShareAlike 3.0 USA:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license.
Identifiers
Publisher
Release Date
2015
Language
English

Content Metadata

Subject Area
Abstract
This is the third (and final) quarter of the organic chemistry series. Topics covered include: Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes of carbon compounds. Index of Topics: 01:05 - Ways to Draw Glucose 02:10 - Chair Conformation 09:01 - Chair to Haworth Projection of Glucose 11:35 - The 5-Membered Ring Cyclic Hemiacetal Form of Fructose 14:54 - Drawing 5-Membered Ring Cyclic Monosaccharides 20:43 - Properties of Anomers: Mutarotation 33:42 - Formation of Glycosides 44:16 - Hydrolysis of Glycosides 47:02 - Reactions of Monosaccharides as Alcohols: Ether Formation
Conformational isomerism Glucose Ionenbindung Chain (unit) Carbohydrate Carbon (fiber) Hydroxyl Chemical reaction Wine tasting descriptors Electronic cigarette Methylgruppe Hydrogen Computer animation Functional group Molecular geometry Thermoforming Isotopenmarkierung Mannose Process (computing)
Glucose Furanosen Ionenbindung Left-wing politics Chain (unit) Carbohydrate Hydroxyl Quartz Alpha particle Optische Aktivität Deterrence (legal) Hardness Colourant Beta sheet Monosaccharide Mixture Pentose Fructose Selenite Ketone Carbon (fiber) Ice front Aldose Chemical reaction Solution Ketosen Wine tasting descriptors Water Hydrogen Computer animation Functional group Hexose Aldosterone Cobaltoxide Mixing (process engineering) Pyranose Thermoforming Isotopenmarkierung
Glucose Sense District Chain (unit) Syrup Carbohydrate Secretion Hydroxyl Wursthülle Quartz Optische Aktivität Alpha particle Water Computer animation Beta sheet Chemical structure Mixture Thermoforming Calculus (medicine)
Glucose Sense District Chain (unit) Carbohydrate Hydrogen chloride Hydroxyl Alpha particle Optische Aktivität Beta sheet Monosaccharide Mixture Cell membrane Biochemistry Hydrocarboxylierung Asset Veresterung Carbon (fiber) Aldehyde Carbonylverbindungen River source Chemical reaction Wine tasting descriptors Glykoside Acid Computer animation Functional group Thermoforming Methanol
Glucose Acetate Ionenbindung Alcohol Reaction mechanism Chloride Methylgruppe Alpha particle Optische Aktivität Electron Hydrolysat Beta sheet Active site Setzen <Verfahrenstechnik> Hydrocarboxylierung Walking Asset Carbon (fiber) River source Solution Wine tasting descriptors Glykoside Acid Computer animation Functional group Penning trap Base (chemistry) Thermoforming Methanol
Hydrocarboxylierung Biosynthesis Reaction mechanism Carbohydrate Hydroxyl Alpha particle Lone pair Acid Computer animation Electron Functional group Beta sheet Cobaltoxide Methanol
Glykoside Computer animation Reaction mechanism Methanol
Acetate Biosynthesis Alcohol Carbohydrate Resonance (chemistry) Hydroxyl Ether Methylgruppe Molecule Solvent Hydrolysat Gemstone Monosaccharide Oxide Silver Sodium hydride Iodwasserstoff Dimethylether Concentrate Methyl iodide Chemical reaction Wine tasting descriptors Glykoside Hydrogen Acid Computer animation Separator (milk) Base (chemistry) Verdünner
Computer animation
we're gonna get started we're gonna talk some more about carbohydrates today talk about how to draw carbohydrates and then reactions of carbohydrates does anybody have questions before we get started I did not get the file back from the midterm I anticipated getting that by about usually I get it about 6 o'clock at night so maybe tonight at about 6 o'clock at night it's late because of the holiday questions anybody all right ok so we left off last time talking about how yes you have a question ah sometime today or tomorrow morning early ok all right so we want to know how to draw Fischer projections of sugars we know what we want to know how to draw epimers of sugars we want to know how to draw an immersive sugars we all want to be able to draw Haworth projection and a chair and a chair conformation for sugars and what you're gonna do is you're gonna memorize glucose you're gonna memorize the open chain form of glucose and then you're gonna memorize the chair of glucose which is really easy because all the other groups are equatorial and then you're gonna make changes from there and that's the easiest way to do it you can also certainly if you want to go through this whole process for I'm drawing a six membered ring you can certainly do that but I think it's a little easier just to remember what glucose looks like and then for the Haworth projection you can either memorize the Haworth projection of glucose or if you do it like I do I draw the chair and then I kind of meant mentally flatten the chair in my mind and that's what I'm doing on the next page so we left off last time doing that so let's go to the next page so I can show you what I mean so we're doing d-mannose to see two epimer of glucose I have the chair of glucose memorized and and this is beta d-mannose and so this is beta that's the wrong amount here okay so this is the beta anomer you will recognize this is the beta anomer and so so since mannose is the c2 epimer of glucose i'm good it's just going to draw the chair of glucose and then you got to know how the numbering goes so the anime our carbon is number one so the anomeric carbon is carbon number one for glucose all right so it's beta so that means that this hydroxyl is up that's carbon number one this is carbon number two I'm gonna put the two there cuz that's where my group needs to go and what you're gonna find is that depending on how you draw you draw your chairs like I didn't do a very good job on that this is the chair that I have trouble with drawing and so I don't do it as well as I do the other chair so I'm going to just kind of move this over so at carbon number two rather than the hydroxyl being equatorial it's going to be axial I'm drawing in all of the other hydroxyls of the ch2oh group depending on how you draw your chair classically you're supposed to tilt it this way and what I usually do is draw it like that because it gives you a little more space depending on how you draw your chair you might have trouble fitting it what you really want to be careful of is not to make that group look axial so it has to be bent as much as you can bend it right here because if you draw it straight up and down parallel with the edge of the paper you'll get it marked wrong no matter what else you've done you get it marked wrong because on this bond on this carbon right here axial is down so your equatorial need to look equatorial your act seals need to look axial and if you just draw this coming straight up you'll get it mark wrong this is not okay now I left hydrogen's off because I think it's pretty clear what's equatorial here and what's axial but you may want to draw some of your hydrogen's in if you want if you you know some of you draw really bad chairs so you're gonna have to work on that before the final okay so and it has to be really clear so what I sometimes get people doing is they're not really sure whether it should be axial or equatorial they kind of draw it halfway in between you know it's a hoping that they'll get a sympathy points so if the grader has to look to the person next to them and say do you think this is axial equatorial that's wrong okay so in other words if this bond is going out at this angle right here everybody following that angle automatically it's wrong no matter what else you've drawn so this needs to be equatorial so here here's what we're going to look for this bond right here should parallel this bond this bond right here should parallel that bond okay this bond right here hard to do it but that should parallel that bond also the other way to look at it is if I put a plane of symmetry right here this bond angles should be it this should be the mirror of this bond angle the mirror image so however you want to draw it it has to be clear but you need to be able to draw a chair clearly so some people they'll just draw this out at an angle that's not an angle and they'll label this is equatorial this is axial you don't you don't need to label it you need to be able to draw it so it looks that way okay I know it's been a long since time since we've drawn chairs but need to be able to do that okay and the other thing that I see that students doing is putting a bond here let me draw it and not putting hydrogen's on so like this okay that's wrong because those are all methyls now that is not that is not beta d-mannose okay those are methyls so please make sure that if you're drawing bonds and you don't put anything on the end it's a methyl so if you want to add hydrogen's you can certainly add hydrogen's where you're going to get into trouble is these middle carbons here when you're drawing so these middle carbons is sometimes hard to fit things in okay the other thing you want to do is sometimes you will you'll see them drawn in books let me erase this one and then we'll we will refix it so like for example if I go up like that see that okay if you draw it like that that means that now we have if you do it like that that means that this carbon now is bonded to four different things do you see that if you it the intersection of any two lines is is a carbon so if you're gonna draw it like that then you need to break the
back bond so I'll do that I'll erase this back on here and I'll move that a little bit so I think it might be easy you break the back bond right just like that that means that um this is coming this is in front of that but they're not bonded together you don't want to break the front bond because then you're kind of doing like a little MC Escher thing going on there just can't possibly be that way so you can either make this bond really short like I did that works or you can break the bond behind it okay so it's it's you it's your it's your points on the test so you want to make sure that that's clear and if you want to draw it and come show me and see if it's clear I'll certainly let you know all right so now we also have to draw the Haworth projection and what I like to do is I like to just flatten the chair so so now either memorize Haworth of glucose and to make changes or flatten the chair all right so I'm going to add some more hybrids of hydrogen's here so you could see how I'm flattening the chair so in a Hayward's projection the ring oxygen is in the top right so our chair is going to exactly line up we wedge this guy right here and now all the bonds are straight up and down this is carbon number one and so it's going to look like that and so what you're looking for here is when you flatten the chair notice that this hydroxyl is up above the hydrogen it's on the same carbon so it's up this hydroxyl is also up oh that sounds like that's my ring but it doesn't sound like it's coming from here you know somebody else's okay so that hydroxyls up this is up above the hydrogen that's on the same carbon this hydroxyl is also up above the hydrogen on the same carbon this hydroxyl is down below the hydrogen that's on the same carbon and this ch2oh is up and this ch2oh is always up for D sugars so you're gonna make sure you get that right so that's all I'm doing here is I'm looking at this this hydroxyl is up this one well this hydroxyl is up so that's carbon number one carbon number two carbon number three the hydroxyl is also up carbon number four the hydroxyl is down so these are all straight up and down and then carbon number five this ch2oh is coming up and of course we want to make sure and I'm just going to change color so you can see we want to make sure of course that we put our hydrogen's here so just like that so guaranteed you will have a problem on the exam like this where you'll have to draw the chair and the Haworth and the Fischer okay so make sure you know how to do that questions anybody all right alright let's talk about five evergreen form of fructose this is your least favorite so not all sugars form six-membered rings them in their hemiacetal form many aldo pentoses and keto hexoses form five membered rings instead alright so this is who recognizes this what's this what is this that what is the Fischer projection of let's see fructose right I know it was right on the tip of your tongue d fructose okay so how do we know it's d-fructose so we have ch2oh on the bottom it's right right left if it's glucose this is a hydroxyl and it's right so it's right right left right but this is a ketose and so instead of a hydroxyl here it's a ketone that's fructose so fructose remember the whole bottom part of fructose the bottom one two three four carbons are identical to glucose so need to know that alright so we can we can cyclize here so notice it looks a little different here we now we got to find our animerica Arbonne and we're looking for a carbon that's bonded to a hydroxyl and in Oro thats going to be right here now remember with glucose and the six membered ring this was a hydrogen but but we're you know what this is this is an aldose so instead of the hydrogen we have the ch2oh so we actually have 2 CH 2 OHS here so there's our an American and so the hydroxyl can be up or the hydroxyl can be down if the hydroxyl is up that's beta if it's down it's alpha so this is beta D we could call it fructose or we can call it be more specific beta D fructose furanose and all the furin a furanose tells us is that it's fructose that cyclized into a five membered ring and then we have here alpha D fructose furanose all right so let's label the anomeric carbon here so we know what that looks like so remember the anomeric carbon is a hemiacetal carbon it's the hemiacetal carbon alright and so this ch2oh right here is always up for the D sugars okay and so we can draw the five membered ring cyclic monosaccharides using the same strategy that we used with glucose it just looks a little bit different but this is what it would look like here and so let's draw it and as we go mentally lay the Fischer projection over on its right hand side groups that are we're on the right or down and groups that are on the left are up so let's draw it right here
and I'm gonna throw all my hydrogen's on here okay so we're gonna mentally lay that down on its side I'm gonna number first before I do that 1 2 3 4 5 6 so 6 carbons and I'm gonna lay that down on its side I'm going to kind of curl it up a little bit like it's going to cycle eyes and I will wedge this so it's kind of sticking out here so when I lay that on its right-hand side I have the ketone here I have the ch2oh so let me number that for you again this is 1 2 3 4 5 and then let's draw a carbon number 6 so that's carbon number six okay so when I lay this down and its side and I'm just like it's almost like I'm knocking it over if this is going down on its right-hand side which is what I've done here if I look at carbon number three the hydrogen will be down the hydroxyl will be down on carbon number four the hydroxyl will be down on carbon number five so let's draw that in so carbon number three hydroxyl is down again I'm going down this direction laying in on its right-hand side hydroxyls down hydroxyl here is down on carbon number four on carbon number five the hydroxyl is down and then we of course we want to draw our hydrogen's in so that's what it would look like and we need to rotate because if we would keep it like this then what's going to cyclize is this oxygen that will make a six membered ring but for this particular ring system we're making a five membered ring and so this oxygen has to rotate so that it's where the ch2oh is okay hard to do that rotation but if we're drawing D sugars that's this will just ch2oh will always be up yes should be a no H where oh yeah yeah yeah oh gosh I'm drawing deoxy ribose oh that's bad okay so yeah we want to fix that okay is that better all right so we're gonna rotate this if you don't know how to do the rotation very well again doesn't matter because we know that the ch2oh is always going to be up so when we do this rotation everything down here will stay the same all right so that ch2oh group is now up and it just made my carbon disappear okay so that looks like that hydrogen down and we're ready to cycle eyes hydrogen here hydrogen here and now we're a directly in line to cycle eyes all right and that can detect the carbon eel from the bottom it can also check the carbon eel from the top okay so those are that's how we get our to an immerse and so we're going to get baited d-fructose urinals and then we're gonna get also Alfa d-fructose your nose alright questions anybody about how we do if I remember green cyclisation alright so the next thing I want to talk about is mutarotation something completely different well not really completely different but alright so if we have a solution of d-glucose and we have it in water and we allowed to reach equilibrium so it doesn't matter which which glucose leads to it's a solution of d-glucose it's a hectic it's going to contain an equilibrium mixture of alpha d glucopyranose beta-d-glucose pyranose and their intermediate open-chain form that's the equilibrium mixture and so here we have the Alpha anamur this is open chain I don't have the open chain drawn in a Fischer projection because it's going to be cycle izing so I want it kind of in position to cyclize and then we have the beta anamur so what's going to happen this is a reversible reaction and so this is this is going to this is going to cyclize to make either alpha or beta and then it's going to open back up so it's opening closing opening closing opening closing okay back and forth so you could start with this and you'll still get the same equilibrium mixture you could start with open chain completely you'd still get the same equilibrium mix you can start with the Alpha anamur and you could you'll get you if you allow that to sit in water you're going to still get the same equilibrium mixture and I'm going to show you that right now all right so those are equilibrium mixture and let's label that in equilibrium all right now sugars are notoriously difficult to work with and crystallize I don't know for science fair projects if you've ever tried to grow crystals of sugar has anybody had any luck can I see a show of hands of people who have had luck doing that it's kind of hard isn't it okay so you you get sweet what happens when you make when you heat sugars up so when you recrystallize something you put it in solution you heat it up you get everything to
dissolve and then you'll allow a crystal to grow and if the crystal won't grow you put in a seed crystal and then the crystal grows on the see crystal the problem with sugars is they like to form syrups and crystals don't like to grow very well out of syrups and so maybe you ran into that when you were trying it anyway so so but if you're very good at this and you crystallize if you've got some good seed crystals and you crystallize below 98 degrees centigrade I'm pretty sure those of you who have grown the secret that done it with the seed crystals haven't grown pure alpha anamur or pure beta anamur cuz that's pretty tough to do you can also crystallize below above 95 98 degrees and if you do very crystal you're very careful crystallization below 98 degrees you can isolate the pure alpha anamur as crystals if you very carefully crystallize above 98 degrees you can isolate the pure beta anamur so after all of that hard work of isolating those pure an immerse if you take this and you put it back into water so by the way the pure alpha anamur has an optical rotation of plus one twelve point two degrees and the pure beta anamur has an optical rotation of plus eighteen point seven degrees that's how you know you have pure alpha and how you know you have pure anamur but when you add that back into water after all that careful work what you're going to find is the optical rotation is going to gradually decrease upon standing and you're going to the optical rotation once it gets to 50 set 52.7 it's going to stabilize at 50 2.7 if you take the pure beta anima and you do the same thing what you're going to find is the optical rotation now is going to gradually increase upon standing until it stabilizes at optical rotation of what 52.7 okay so the 52.7 is this equilibrium mixture up here that's the optical rotation of the equilibrium mixture of the Alpha the beta and the open chain form okay so that's what that that's what's going on there so this is an equilibrium mixture of the Alpha open chain which incidentally is a very small amount in the open chain and the beta an immerse alright and so this change into uh in specific rotations to a mutual value is called mutarotation and if we have these numbers here we can actually calculate how much alpha how much it be that we have in the mixture so something you want to know how to do I haven't decided whether I will put it on the final or not if I do put it on the final you will need a non graphing calculator and I will let you know so you'll know B before you take the final whether you're gonna have to do one of these calculations okay but right now I'm going to show you what it looks like it's not a hard calculation so if you're zhenia if we have any non math people out there it's not a hard calculation so how much alpha beta is there in the equilibrium mixture this can be calculated as follows I'm gonna let a be on the fraction of glucose as the alpha anima I'm gonna let B equal the fraction of glucose as the beta anomer and so the fraction of glucose as the alpha turns it's optical rotation which is plus 1/12 0.2 degrees plus the fraction of glucose as its beta anomer which is it has an optical rotation of plus eighteen point seven degrees and that's equal to 52 we are ignoring the open chain because it's such a small amount we are ignoring the open chain form so ignoring open chain for him because there's only a tiny amount and I've got to tell you in a second how much open chain we have and you'll see that that was a good approximation to completely ignore it all right so we have two unknowns one equation we do know since we're ignoring the open chain form that a plus B equals 1 right fraction of alpha a fraction of beta equals 1 so a plus B equals 1 and I'm going to solve for B B equals 1 minus a and so now I have two equations two unknowns I'm going to be able to solve it a times one twelve point whoops 1/4 twelve point two degrees plus and for B I'm going to plug in 1 minus a times its optical rotation 18 point seven degrees and that's equal to 52 point seven degrees and then I'm going to solve for a and what I'm going to get is a equals 0.36 so that's the fraction that is in the alpha affection of the Alpha anamur so in order to get the percentage it's the fraction times 100% so the Alpha anamur is 36% and so the beta anomer is 100 - 36 64% all right so does that make sense does it make sense if let's look at the lookit go look at the structures again if this wasn't scroll up for me does it make sense that the beta oh the scroll bars terrible on this does it make sense that the beta would be favored what is the beta anomer rehab that the Alpha animo doesn't have yeah it has equatorial hydroxyl so it's more stable the beta anomer is more stable than the Alpha anamur it's not necessarily going to be the case for all of the sugars you're going to get different percentages for the different sugars because in the different sugars some of these hydroxyls are going to be axial so it kind of changes things doesn't it but for glucose definitely beta is favored all right so that makes good sense
and so for the beta the anomeric hydroxyl is equatorial and so you expect the beta anomer to predominate all right so let's talk about some of these other forms of glucose deke glucose can also cyclize into two furanose forms so five membrane forms but furin arts forms constitute only 0.1 percent at equilibrium so alpha this would be alpha d glucopyranose zero percent so we didn't have to worry about that open chain form it looks like I don't have the number here but it's less than one percent I know it's less than one percent and then we have beta-d-glucose furanose 0.14 percent so for D glucose it overwhelmingly likes to be in the beta the beta anomer of a six membered ring okay questions on mutarotation anybody yeah point four point one four percent it's really low so six membered rings are more stable than five so I'm not surprised about that yeah so yeah that is this is point four and four percent not fourteen percent yeah that's the optical rotation of the pure animal which I got from right here see that yeah does that make sense now and the 52.7 is this value right here that's going to be different for different sugars yep you would be given oh yeah of course of course that would be given more questions on we do rotation yes no the open chain is less than 1% yeah it's less than 1% it's not less than 0.1 4 but it's very small I don't remember off the top of my head and I know that my two TAS don't remember off the top of their head it's less than 1% so it was okay for us to ignore that value all right so let's talk about start talking about some reactions of monosaccharides as carbonyl compounds so maybe if you looked at and learned glucose in in bio you probably thought oh how is it acting as a as a carbonyl compound it's not a carbonyl compo but it certainly is right so even though glucose is mostly in a hemiacetal form so it's all cyclized remember its opening and closing and opening and closing so when it opens up it can react as a carbonyl right it's an aldehyde so it doesn't matter that most of it's in the ring form and not going to react as soon as it opens up they can react as a carbonyl if it can't open up then it won't react as a carbonyl and that's what we have when we have a glycoside so that's the first thing I want to talk about so here we have this and I'm just going to draw a squiggly line here that means that I have a mixture of alpha and beta mixture of alpha and beta is the squiggly line and so at this this is a hemiacetal and of course the hemiacetal carbon is right here it is the carbon that's bound to a hydroxyl and an O R group simultaneously all right if we take that and we add methanol and catalytic acid we'll just say HCl here or h3o plus or you could say h2 so4 catalytic what happens to a hemiacetal when we put it in methanol with a catalytic acid what happens to it you can make an asset alum it right okay so and that's so that's what we have here and so we can make an acetal here again i'm going to just show this squiggly line for a mixture of alpha and beta so this is now an acetal all right and so now that it's an acetal we're gonna we're gonna name this so we're gonna name this kind of like you do with esters those of you who looked at the podcast and decided to actually learn how to name carbonyls which was not everybody but we named this kind of like an ester so this group is named first and then the rest of it is named as an as in rather than an eighth for an ester it's an O side for a sugar so this is not methyl alpha D well since it's alpha let's draw it as alpha let me go
erase that let's fix that sorry if you you wrote that in pen I do apologize o ch3 that's alpha right so I give you second to fix that so methyl alpha D gluco PI R and side so it's kind of cool because these names are really descriptive so we have a methyl it's it's a methyl glycoside it's an alpha so we know that that at the animerica Arbonne it's alpha and we know it's D glucose and we know it's in a six membered ring and so there's a lot of information there and it turns out that you get about 66% of the methyl and you'll also get about 33% of the beta anomer all right so this bond right here is the glut whoa not that one this bond right here is the glycosidic bond and the the group that you put on here this right here that's called an egg like own and in a guy cone is a group that is bonded to the air America carbon of a glycoside so methyl GU co-primary sites do not undergo room meter rotation and they are stable to base but hydrolyze easily an acid solution just like assets house same as acid house so there is no there is no meter rotation we don't get the ring opening and closing and opening and closing so once this forms methyl alpha D glucopyranose side its stuck as the alpha anima it cannot go back to the beta they don't go back and forth you can't there's no mechanism by which they can open up you can hydrolyze the glycoside but then it's not a glycoside anymore alright so they're stable debates just like acid towels and they hydrolyze easily in acid so let's look at the mechanism here and if you know the mechanism for acetal formation which most of you got on midterm 1 and assuming that's still in your head then you know this okay so this is like half the half of the mechanism for asset owls and I'll just start with the Alpha here just for fun so we protonate um I'm if I have catalytic acid I'm going to have some of my alcohol protonated if we use h3o plus you could also do this with h3o plus not very many mechanisms in this chapter I think this might be the only one which means that's a likely candidate for the final just saying not to mention it's it's it's also you know cumulative I'm trying to make the finalist cumulative as possible okay all right so we're you're gonna encounter the same intermediate when you go back and look at midterm 1 and you look at your asset L mechanism and you say to yourself how did I even do that this is the same thing and so what's going to happen is electrons are going to come down and we're going to kick this off as a leaving group and we get something that looks like a protonated carbonyl it's not a protonated carbonyl but now we're going to have methanol attack all right so and I'm just going to go ahead and draw again the Alpha here but I could get beta also and so this is the alpha I'm gonna get beta also and then in the last step I will deprotonate so depending on what the acid here is I'm just gonna use methanol if it was hydrochloric you could deprotonate with the chloride now
notice I have left off all of the extra
ethyl hydroxy groups I'm just trying to focus on the group that's changing here so I left I left off all of the other ones and if I have this mechanism on the final it would be the same thing you're just going to draw the ring like this without all the extra hydroxyls no reason to take the time to do that yep you can't just depends on what the acid here is what the acid is given all right so that's from the methanol coming in from the bottom if you attack from the top face of this ring so if the top of face of the carbonyl you get the beta in or and so we're not really going to talk too much about why betas of why alpha is actually favored here but you might want to think about you know if you think about when if this is coming in from the top it's approaching this direction we have lone pairs on this oxygen that may affect how this methanol wants to come and attack it's preferring to attack from the bottom rather than coming in on this side so just something to think about but it will not be testing you on that alright questions anybody on that mechanism so you should also be able to draw the reverse take a glycoside and hydrolyze it to get back your your sugar right it's just the opposite so I want you to be able to do that also now look at that I added the sin I didn't used to cover this but I added it in so we could do this though okay what we're gonna do is we're just gonna we're gonna just draw in the necessary things I'm going to take the Alpha and I think these are the only two mechanisms in this chapter if I'm not mistaken here I'm gonna use hydronium mine so one of these two huh you can handle that you guys really usually do really do well on mechanisms - its its synthesis that's the trick right that's the thing okay so we're going to protonate that that group's gonna leave because we need to replace that with a hydroxyl all right so we're gonna have electrons on oxygen come down kick that off and I will tell you just from my experience if
I put this mechanism one of the two of these which I usually do probably about 90% of the students will get it right okay because you guys do really well on mechanisms maybe you don't believe me but I I see it so all right then this is
going to check so in the previous one we had and then the methanol attack is we're trying to make a glycoside now we're trying to hydrolyze a glycoside
yeah we're almost there now we can't undergo mutarotation cuz now it's an it's a hemiacetal so in order to go undergo mutarotation it has to be hemiacetal it can't when it's an acetal alright questions on that one anybody yeah Oh have the would have that come off uh yeah if you just want to have this come off instead and just learn the carbo cation it's also okay to do that it's just a resonance structure of what I've drawn here alright alright so that's my jewel assistive glycosides let's talk about reactions to monosaccharides as alcohols so we know from Chapter nine I know that was a while ago but when we did Williamson ether synthesis what did we do we deprotonated the alcohol with sodium hydride and then we did like if we want to make the methyl ether we would use methyl iodide so this is the same idea it's just that they use with sugars as silver to oxide of silver not silver to oxide silver oxide is used instead of sodium hydride okay but as you can see this is now in a Satele but all of these other hydroxyls we can report we can make ethers out of those by deprotonating and attacking with methyl iodide so let's draw the profits through the product of that all right so this is now going to be oh oh well just student and methyl to get saved face here Oh methyl ohm ethyl o methyl so notice I have a little bend here for that ch2 there and let's draw some hydrogen's in to make this look a little better all right so so these guys all of these this one this one this one and this one those are now ethers methyl ether they are stable to base and dilute acid what did we have to do to cleave a regular ether I'm not talking about an epoxy but a regular ether back in chapter 9 would we have to use do you remember that hot concentrated hydrolytic acid hydroiodic acid has a pKa of like minus 9 or 8 9 or 10 so it's they're pretty stable that's why we use them as solvents all the time that's why you guys use them in the lab when you're doing separations set in the SEP funnel this one on the other hand is not an ether is it what is it what is it part
of to NASA tell this is part of a NASA tell they're for sensitive to dilute acid so if I treat this molecule with dilute acid the acid towel is going to the glycosides going to get hydrolyzed all the rest of the ethers are going to stay exactly the way our they are and we'll
talk more about that next time
Feedback