in this video we're going to talk about uh cycloalkanes so let's get started so usually when we talk about the cycloalkanes we're going to talk about like three member rings four member rings five member rings six member ring those type of ring chemistry that we're going to talk about in this video just to let you know that usually in nature five or six member rings are more common because five or six member rings are usually more stable more stable type of organic cyclic compounds smaller rings such as three and four member rings are not very stable they are very very unstable uh that because those three or four member rings they have a bond angle which is lower than 109. 109.5 degree and when an sp3 carbon has a bond angle lower than 109.5 degree or higher than 109.5 degree that type of ring experience certain type of strain we usually call angle strain and in those smaller ring the bonds are not kind of straight they are um they take the bend shape usually those type of bonds we can ban on a bonds if you have a let's say carbon carbon bond just a straight carbon carbon stick uh single bonds so two sp3 orbitals they can do it head-on overlap so you will have a good overlap to form a strong bonds and when you have a ring like three-member four-member ring will happen that sp3 orbitals the paint such way just like a banana and they form a bond carbon carbon bond that way as you see here the two sp3 orbitals they have a very poor overlap here so banana bonds are usually weaker bond than a normal carbon carbon sigma bonds so if you look at here so this is three member cycle alkene weaker cyclopropane the bond angle between this let's say this carbon this carbon and this carbon is 60 degree you have cyclobutane the bond angle again the carbon carbon carbon that is 90 degree cyclopentane the bond angle is 108 and cyclohexane the bond angle is 120 degree as as i said in the previous slide when you have a bond angle uh more than one or 9.5 degree or smaller than one or 9.5 degree that ring experiences certain type of strain we usually call angle strain so again if you look at here this carbon all the carbons in these rings are sp3 hybridized when you have sp3 hybridized carbon usually the bond angle is 109.5 degree so for cyclopropane case it is like as it is 49 degrees smaller than uh so you can see if it is sp through them is 109 that's a ideal bond angle but it is deviated by 49 degree cyclobutane as it is deviated by 19 degree and cyclopentane case it is deviated by one degree and cyclohexane case it is deviated by 11 degree so you can see this is 11 degree more than normal sp3 bond angles this is one degree lace uh the normal um sp3 bond angles and here is like 90 degrees shorter than normal sp3 bond angle so all these strings are under stress so this angle we usually call angle strain again angle strength is the type of strength that arises when a bond angle is either compressed or expanded compared to its optimal value so that is we call angle strain so in cycloalkane there are three types of strain one can actually see one is the angle strains usually as i said before it usually results from deviation from ideal tetrahedral angle of 109.5 degree there's another type of strain that we talked about earlier torsional strain it is a type of strength that results from repulsion between bonding electrons of one substituents and a neighboring substituents so here you can see the picture here if you have let's say this carbon and these hydrogens if you have ch bonds or the sp3 orbitals and the one is orbital zx they form this covalent bond ch bond so these two long lone pair electrons in this covalent bonds and these two one pair of the electrons these if these two bonding electrons they if they are close to each other then they will repo ripple each other so this type of strain we call torsional strain and the third type of strain we call straining his static strain is type of strain that results from atoms or group of atoms approaching each other too closely if you look at here so this is uh ch3 you need so one of the hydrogen is pretty close to another hydrogens so when they are too close to each other then they will rebuild each other and that type of strain we call static strain so usually six member rings are almost free of strain in a chair conformations if you look at this table you will see this here the cyclohexane the that is zero kilocalorie per mole or zero kilojoule per mole so total strain energy per cycle action is zero the next one is uh the next one is five member ring which is 25.9 kilojoule per mole that's the total strain energy but if you compare the cyclopropane which is 114 is very very high number cyclobutane is very very high numbers but cyclopentane which is 25.9 and that's the the second stable of ring cycloalkyl ring the cyclohexane this is zero kilojoule per mole so as i said before if you think about the cyclox in planar structure the bond angle carbon-carbon bond angle is 120 degree then how come this gave you zero total strength energy so then that can be explained if you look at here in this if you if you pay attention on this structure in the on this slide you see that here is the cyclohexane in one thing that this is a planar structure where each carbon has two hydrogens and then there are six carbon so this planar conformation all the carbons and sp3s carbons and the bond angles of this carbon carbon bond angles are 120 degree if you consider the cyclohexane as a planar conformation then the total um the calculated strain energy would be 12 kilocalorie per mole torsional strain that because as you see here these hydrogens these hydrogens that are next to each other and they're close to each other so these bonding electrons will repel this bonding electron so there are 12 of them so you can see it will be around 12 kilocalorie per mole torsional strain but if you consider the cyclex and bring in this chair conformation form then just like a chair then the in that case the cycle actions uh adopts the chair conformation to allows his bone angles to be 109.5 degrees so the bond angle here the carbon carbon carbon this bond angle is 109.5 degree which is exactly the bond angle of sp3 carbons and it has zero torsional strength so it means the cyclohexane it will not stay in this planar conformation form usually in nature they stay in this chair conformational form because that way they will have no torsional strain and it would be a stable cyclic compounds now the question is why would the chair conformation don't have any um torsional strain so if you look at this chin chair conformation of cycloactions again it says c6 and h12 6 carbons and 12 hydrogens but if you want to look at this structure in a little bit different way if you could look at along these and along this axis you can see one and five carbon um so and then you can draw the newman projection you see this is your carbon one that's the center the front carbon here is the carbon five is your front carbon and then you have two hydrogen so these two hydrogens back carbon is carbon two that has two hydrogens one ring so that's a two hydrogen and one ring that's a carbon number three and that's how this is the back carbon here is four here is the ring carbon and those two hydrogens what can you see here from this animal projections if you pay attention we can see here this there this hydrogen is anti to these hydrogens this is anti to this hydrogen this is anti to that and this is anti to this this anti to that it's pretty much kind of a staggered confirmation that you have learned in a previous video when you have a staggered conformations it means there is no torsional strain because the bone bonding electron cannot see the neighbor bonding electrons pretty close so this is why when they're 180 degree apart so they won't see it and you won't have any torsional angles so this is why the shear conformation has no torsional strain but again if you write the planar structure like this then they will have a torsional strain which is around 12 kilo calorie per mole and here is um the ball sting model for the chair conformations a black circle here represents the carbon white ball represents here is uh represent here are hydrogens so now how to draw the cycle x in uh in the chair conformation form so here is the cycle x and share confirmations so usually couple of things that you must need to remember in order to draw the cycle x in in the chair conformation form the first is in the chair you have to um you have to remember alternative often down carbons so in the chair we see this is the up carbon the down carbon up carbon down carbon up carbon down carbon so all the carbons arrange in this way alternatively up and down carbons then each carbon in chair has an axial and equatorial bonds if you look at here in this carbon here this is an axial bonds axial bond and this is the equatorial bonds so usually the vertical bonds we call the axial bonds and the other bonds we call equatorial bonds horizontal bonds kind of we couldn't call it as equatorial bonds so again this this carbon it has a vertical bond this way so that's the axial bond this is equatorial bond this carbon if you look at it here you see this is axial bond this equatorial bond so each carbon in the chair conformation has two types of bonds again remember the vertical boundary coaxial bonds and equatorial and the horizontal bond type that we call equatorial bonds so now the question is of carbon that's another thing that you need to remember here now up carbon has up axial bonds and down carbon has down axial bonds so if you look at here this is the up carbons of carbon has up axial bonds and down carbon here tested the down carbon has down exhale bounds up carbon up axial down carbon down exhales that's how it goes and for equatorial case of carbon has down equatorial if you look at this is the up carbon this is the down equatorial and then down carbon here they have up equatorial bonds so up carbon has down equatorial bond down carbon has obvious bonds so now notice axials are alternative up down up down and equatorial alternative down up down up so that's how the the equatorial and axial positions are uh are drawn here in the chair conformations so again as i said the axial of carbon has the axial up and then equatorial down and that's a a e we always represent that way exhale up equatorial down an equatorial case for in this case equatorial up and then axial down so that if you look you start with the up carbon then you will have axial up and then equatorial down then you start with if you start with the down carbon the down carbon will have equatorial up and exhale down so if you have cycle x and if you want to write what would be the combinations here like how would you correlate the axial substituents with the equatorial substituent so you have to remember this one so axial up equatorial down and this is alternative carbon x allow your control to maxillary control down and in the middle you can see equatorial up exhale down equatorial lab exhale down that's how you have to remember the position of the substituents on the shear conformations now the question is what will be the geometry relationship of axial and equatorial bonds if you have substituents so if you have substituents how do you write those uh axial up and axial substituents and equatorial substituents so let's solve some problems together so before we do that i would like to introduce with the two other uh concept that's a trans and cs if you have a ring with two substituents and if the two substituents are going in the same directions either both up or both down then they are called cis and if they're going in opposite direction they are called trans if you look at this structure here you can see you have two chlorine atoms and those are drawn with the dash bond dashboard usually points down so it means those two are below the plane and if you look at here you can see those two are pointing down means those two are going in the same direction so we can call it cs so c is one two dichlorocyclohexane so that is the name of this compound if you look at here this is we um have carbon chlorine bond the carbon current bond is shown here with the wedge bond that means pointing up and these two chlorine are pointing in the same direction in the up directions we call cs1 to dichlorocyclohexane if you have this one again those are cj one three dichloro cyclohexane again the chlorine and this current they're pointing down this chlorine this current they're pointing up this is why we call c's so this is the definition if two substituents are going in the same direction we call uh cs if two substituents are going opposite directions we usually call transfer in this case if you look at here this is going down this is going up so they're going in opposite direction we can call it trans so trans 1 to dichloro cyclohexane so that is the name of these compounds here is similarly trans 1 to dichlorocycloaccent because this chlorine and this current they're appearing in opposite directions now we want to draw a chair conformation of c one three dimethylcyclohexane so now we have substituents on the two substituents and they are related by their their c's they mean they are pointing in the same directions so again how to draw the chair conformation of this structure here in order to do that what we have to remember sis means both go both groups either up or downs right so first we need to draw a chair conformation which is the parent chair confirmation c6 and a6 so that share confirmation then you what you have to do you should just number the carbons one two three four five six six carbons here so you number it again you can start the numbering from any carbons if you start from here one two three four five six steps that will also work or if you wanna start from here one two three four five six that's fine so any carbon if you want you can start number it all right so i started here like one two three four five six like that way now what i have to do i have to identify this is my up carbon this is down carbon this is my up carbon this is down carbon this is my up carbon this is my down carbon so i'm going to use that rule up carbon has axial up and equatorial down so this is my up carbon and i can see carbon 1 has up methyl group so i can say this is my methyl group which is up and up carbon has axial up so this is a i place this methyl group and on axial position and this is my hydrogen so the hydrogen's right here that's my hydrogens and then i see my carbon three which is my up carbon half carbon axial up and this methyl group is also up so i can see the methyl group i can put it on axial positions and now what i can see here now we can i can see this methyl group is up and this methyl group on carbon number three is also up so both groups are up that means these two ca assist to each other and this is the chair confirmations of 1 3 6 1 3 dimethylcyclohexane so this is how you have to draw the chair conformation for this type of structure so if you want you can try to draw another conformations by placing the first ch3 global equatorial on carbon number one so again if you want if you want you can pause the video and then you can try on your own this problems and then you can check your answer with the answer i'm going to show you now so you can draw the chair conformation first then again you can start numbering from any carbons so i am kind of numbering this way now this time now i am seeing here my this is my down carbon this is my up carbon this is down carbon this is up carbon this is down carbon this is up carbons now we know here is the rule down carbon has axial down and equatorial up so i can see here my this is my axial that should be down because the down carbon and this is my equatorial up so i can put a methyl group on equatorial positions and which is up and it says up here then i can look at my carbon number three carbon number three is also a down carbon again down carbon exhale down equatorial up so exhale down equatorial up so i can put the methyl group in the up position then i will have the chair conformations of one three c is one three diameter side flexing in another form so you can see here this is up this is up and both are up that means both are c to each other right here is in our here is our second problem so draw a chair confirmation of trans one to dimethyl cyclohexane so again if you want to use the trans trans means both group either up and down or down or up so first thing is you need to have your cyclohexane chair structure and then you number the ring carbon one two three four five six again you have up carbon down carbon up carbon down carbon up carbon down carbon and we are going to use the up carbon always have axial up equatorial down so we have up carbon here the axial up and equatorial down so we can put the methyl group up and hydrogens down there again this is a line structure we are not spraying the hydrogens here because it is implied the hydrogen is right there but when you are going to draw the chair conformation you must need to indicate the position of hydrogens and cst this way now we can see here on carbon number two carbon number two is a down carbon down carbon has axial down equatorial off so down carbon again has axial down this is my axial and equatorial up and you can see here this is down so i can put the methyl group there and here is my hydrogens what can i see here in this case i see this is up methyl group here is up and here is the methyl group down so i have up down combination here so this is the structure chair conformations of trans one to dimethylcyclohexane again try to draw another conformation by placing first methyl group on equatorial on carbon number one and again you can pause this video and try to answer these questions on your own and then you can check the answer the answer i'm going to show you in a second so here is your chair conformations uh then you can number the ring again good number any for starting from any carbon so i started this this way one two three four five six and now i can see here my down carbon right here it's a down carbon exhale down equatorial up so axial down equatorial up so i can see my methyl group right here which is up so i can put it the methyl group down there up there now on carbon number two is this is up carbon and up carbon usually have axial up and equatorial down so equatorial downs so i can see here this is down so this is equitable down and what i see here this is the methyl group down here and this methyl group up here so this is down and up combinations therefore this is also the chair conformation of trans one to dimethyl cyclohexane so that take us for another practice problem here so draw the most stable chair confirmation of the following compounds so in this case we're going to draw the chair confirmation first and then we'll talk about how to check the stability for a particular chair confirmations which one which share confirmation will be more stable which is gonna share confirmation release table in our next video first we want to try to in this particular problem we wanna we want to draw the chia confirmation of this structure so what is the rule the first rule is you need to draw the chair confirmations and then remember you need to number the ring so in this case i started numbering from 1 2 3 4 5 6 this way now i have to remember this way that this is my up carbon so this is my up carbon down carbon up carb down carbon up carbon down carbon half carbon usually axial up equatorial down so axial up so if this is my carbon number one the methyl group is up and hydrogen should be equatorial down that height is in the test with carbon number one now if i go this way i can see carbon number three has methyl group down here we can see the carbon number three is an up carbon so it will have axial up and equatorial down and it says the methyl group is down so it means the methyl group should be right there all right so we can see here this methyl group and this methyl group they are trans to each other this is up this is down so they're trans to each other too next is carbon number five chlorine chlorine so this is carbon number five this is up carbon and this is my equatorial down so it means the chlorine here is represented as a is a up up chlorine it's a chlorine which is also c is two carbon number of this methyl group so this methyl group and this chlorine they are both up position they're assist to each other this chlorine and this methyl group they are trans to each other this is up this is down there for uh that pretty much matching the confirmation here um so this is the chair confirmations of this structure so that's all for this video we'll talk about the stability of sci and the chair confirmation ring in our next video