answr
Join / Login
Open Toppr answr on the app

Conformations of Alkanes

Conformations of Alkanes (Butane and Cyclohexane Included)Conformations of Alkanes

Transcript

  • 0:2hi guys welcome to the wonderful world
  • 0:4of hydrocarbons chemistry and here we
  • 0:7are with the main topic of
  • 0:9conformational isomerism in alkanes well
  • 0:12in case of conformational isomerism in
  • 0:15alkanes I guess so you remember we were
  • 0:18talking about some representative
  • 0:21formulas isn't it right so let me just
  • 0:24write down those are representative
  • 0:28formulas are called as projection
  • 0:30formulas what are we called as
  • 0:33projection formulas okay now in this
  • 0:37case what is this projection formula are
  • 0:39going to talk about so this particularly
  • 0:43projection formula just for the time
  • 0:45being just ignore it okay so this
  • 0:47particular projection formula actually
  • 0:49talks about the way I could represent my
  • 0:53molecule in space or as it was in space
  • 0:57okay so in that case how is it so easy
  • 1:1to represent a particular formula as it
  • 1:5isn't going to be in space okay so in
  • 1:8that case there are two types of law
  • 1:10rejection formula which were actually
  • 1:12sure what was called as Newman's
  • 1:16projection formula okay what is it
  • 1:20Newman's projection formula P if I have
  • 1:23abbreviated it as PM whereas the other
  • 1:26one was your sawhorse so in this case R
  • 1:31actually it was talked about as Newman's
  • 1:33projection formula and sawhorse one
  • 1:35happy what is this Newman's projection
  • 1:37formula and sawhorse so basically your
  • 1:42Newman's projection formula talked about
  • 1:44a spherical body or another basis circle
  • 1:48okay which could be shown in this manner
  • 1:54okay
  • 1:56well let me tell you very clearly we are
  • 1:58talking about routine now okay so in
  • 2:1that case Eden is what c3 - ch3 right so
  • 2:5ch3 - TV HD means in this case all of my
  • 2:11lines would end up with the hydrogen
  • 2:14what is all this let me come to you hold
  • 2:18on and the other one okay other one was
  • 2:22known by the name Oh some horse okay so
  • 2:27his projection formula now what did how
  • 2:30did it projected the items or the
  • 2:32location of it in space so it was in the
  • 2:35following manner
  • 2:36where in a straight vertical line or a
  • 2:39slanting vertical line I would say was
  • 2:41taken up okay and since I am talking
  • 2:43about ething this is a magnified view
  • 2:46which we are going to get so I would be
  • 2:48having my hydrogen atom stationed in
  • 2:52this way I guess now you can have a
  • 2:56clearer idea of it isn't it so I'm
  • 2:59having my two carbons over here okay and
  • 3:2all of the other being hydrogen so in
  • 3:6this case if you go to see it's CH
  • 3:8straight a ch3 okay and what does it
  • 3:11show is that these two hydrogen atoms
  • 3:15which are facing vertically upwards are
  • 3:17going to be in the same plane maybe in
  • 3:20the plane of the board okay whereas
  • 3:23these hydrogen atoms are in one plane
  • 3:26again but outside the plane of the board
  • 3:29on the other side on your side I would
  • 3:31say fine so let me depict it as like
  • 3:34this fine whereas whereas these two
  • 3:41hydrogen atoms are on my side Redmon's
  • 3:44outside the plane of the board again so
  • 3:48in this case it was quite simple a
  • 3:49vertical line and these three lines
  • 3:51would represent the positioning of the
  • 3:53atoms very well now why well you well
  • 3:56because that time we did not have an
  • 3:58idea as to this could be done in a
  • 3:59better way this was the ultimatum okay
  • 4:2so in that case if at all I wanted to
  • 4:5talk about a particular position of
  • 4:7being stable or unstable okay or maybe
  • 4:11minimum stability I will represent it in
  • 4:14in this way like the way I have done it
  • 4:16over here so as you can see these two of
  • 4:18them are facing vertically upwards okay
  • 4:21and in this case we got to visualize the
  • 4:25electron cloud okay so imagine carbon
  • 4:30with an atomic number six electronic
  • 4:33configuration one is 2 2 s 2 and 2 P 2
  • 4:35okay so even after excitation and the
  • 4:39hybridization thing which all goes on I
  • 4:41should be having sp3 hybridised more of
  • 4:45carbon right so if it is an sp3
  • 4:49hybridized more that would be
  • 4:51overlapping with the S orbitals of
  • 4:53hydrogen so in that case it definitely
  • 4:56calls out for an electron cloud right
  • 5:0now supposedly if I am imagining this
  • 5:3particular part of it as the electron
  • 5:6cloud of this bonding as a resultant of
  • 5:8this bonding whereas this particular
  • 5:10electron cloud as a resultant of this
  • 5:13bonding all of them are in the same
  • 5:16direction okay none of them is shadowing
  • 5:18each other or anything has happening so
  • 5:21in this case as I can see even if they
  • 5:23move slightly apart okay maybe if like
  • 5:27I'm having this hydrogen away and this
  • 5:29hydrogen over here if at all this is
  • 5:31moving a little bit over here and this
  • 5:33is moving over there
  • 5:34still they Lakefront cloud is there
  • 5:35right now if the electron cloud is there
  • 5:39obviously both of them are negatively
  • 5:41charged if both of them are negatively
  • 5:44charged and they are approaching so
  • 5:46nearby what do you think what happen
  • 5:48clash obviously a repulsion okay so this
  • 5:53is a magnified name which I have given
  • 5:55you wearing a longer vertical line has
  • 5:57been drawn out but then an actual it is
  • 6:0very nearby isn't it we know that well
  • 6:3so now in this case when repulsion comes
  • 6:5in obviously it would question the
  • 6:8stability of the molecule and so if it
  • 6:11is questioning the stability of the
  • 6:13molecule that itself means that this
  • 6:16would be a stable state or a state which
  • 6:19would be very much what I could say
  • 6:23wanted by this particular molecule break
  • 6:27the wings it would get into some other
  • 6:28kind of a rotation or otherwise I would
  • 6:31say and other kind of rearrangement
  • 6:34what would that be that would be
  • 6:37something where in the plains would be
  • 6:41different so that the electron clouds
  • 6:44don't come near and neither do they
  • 6:46repel so in that case what would happen
  • 6:49is this now just look at this one guys
  • 6:55what does it indicate it's very simple
  • 6:58it indicates that this hydrogen cloud
  • 7:1and this hydrogen cloud is oppositely
  • 7:4placed and so are these two hydrogen
  • 7:7atoms so this is providing me a minimum
  • 7:11repulsion if it is providing me and
  • 7:14minimum retention that means a maximum
  • 7:16stability is going in right okay so this
  • 7:21was the way it could be predicted that
  • 7:23yes these molecules can exhibit such
  • 7:26kind of locations and space and hence
  • 7:32they were given at all what was the term
  • 7:35this one was kinda staggered whereas the
  • 7:38other one was called as eclipsed what
  • 7:41was it let me write down this one was
  • 7:43called as staggered conformation whereas
  • 7:46the other one was called as eclipsed
  • 7:50okay fine so conformation as I had
  • 7:54explained you even last time it's simply
  • 7:56the rotation about this single single
  • 7:59carbon bond ok a single carbon-carbon
  • 8:1bond I would say so they are also called
  • 8:3as root ammos okay
  • 8:5whereas what is Newman talking about so
  • 8:8new man is the same thing man okay
  • 8:10it's only the depiction which is going
  • 8:12to deform so in this case I have a
  • 8:14carbon located over here okay
  • 8:16same as behind the circle also okay and
  • 8:19in this case I'm having the electron
  • 8:22clouds located opposite to each other so
  • 8:24this was giving us a better idea as to
  • 8:26what is located in opposite to which
  • 8:28atom animal so due to which we could
  • 8:31visualize we could visualize as to which
  • 8:34of them could be more stable which of
  • 8:36them is least people so this was an
  • 8:39example of again what is it
  • 8:41staggered why because both of them are
  • 8:44opposite
  • 8:46what were we Eclipse then the Eclipse
  • 8:49one would be something like this wherein
  • 8:51I would be having the positioning quite
  • 8:54nearby to say like over here okay over
  • 8:59here and over here right
  • 9:3what was this this was an eclipsed
  • 9:6conformation okay and then Newman I
  • 9:10could represent one more confirmation
  • 9:12which was a resultant of the
  • 9:14intermediate of staggered and eclipsed
  • 9:16so it was something like this so I was
  • 9:19having this H okay whereas my skew one
  • 9:26okay
  • 9:32see something like this okay
  • 9:36so this was called as cue or also called
  • 9:39as gosh so if you don't I want to talk
  • 9:44about the order of stability then
  • 9:46stagger would be the best stable one
  • 9:49followed by gosh followed by eclipsed
  • 9:52the least stable okay fine
  • 9:55now what is the difference and how do
  • 9:58you put it numerically so plot was drawn
  • 10:1out in which potential energy was given
  • 10:4on the Y and my angle of rotation on the
  • 10:6x axis so angle of rotation means at
  • 10:9what angle is the carbon-carbon single
  • 10:10bond going to rotate so in this case I
  • 10:14had 0 60 120 180 so in case of Ethan it
  • 10:18was seen then the conformers say like
  • 10:21eclipse and star staggered majorly whoa
  • 10:24having an angle of rotation of 60 60
  • 10:27degrees each in which I could see that
  • 10:30at one point I was getting a staggered
  • 10:32at the other point I was giving at
  • 10:34eclipsed okay this one was standard of
  • 10:37course right the lower ones and the
  • 10:40higher one was eclipsed in fact in this
  • 10:43case if we could even see that at what
  • 10:48point or at which confirmation is the
  • 10:51molecule more stable so on this plot
  • 10:54itself if you go to see here is my 0 so
  • 10:57below zero is my staggered so that means
  • 11:0it is more stable
  • 11:1right because lesser energy whereas my
  • 11:4eclipses composing of a higher energy
  • 11:7cotan so obviously it is going to be
  • 11:9less stable right and if you don't I
  • 11:12mean if you go to see the numerical
  • 11:14value of the energy differences between
  • 11:16both of them it's twelve point five five
  • 11:18kilo joules per moon and that comes from
  • 11:21where that comes from the energy
  • 11:24differences of these two conformers so
  • 11:28in that case if I put it up numerically
  • 11:30for this sawhorse or rather ways for the
  • 11:32stagger and the eclipsed one in case of
  • 11:35April Eclipse the inter nuclear distance
  • 11:37between these two non bonded hydrogen's
  • 11:39is around 229 Pico meters
  • 11:43whereas in case of staggered it's 310
  • 11:48picometers so now you can imagine the
  • 11:51distance right and the repulsion is
  • 11:53occurring fine so I guess I have given
  • 11:57you a perfect idea as to what is a
  • 11:58conformer and how does it look like and
  • 12:0how it can be blotted right so now we
  • 12:3can move towards the next session to
  • 12:5learn something more about alkenes isn't
  • 12:7it right so see you in the next session
  • 12:9till then thank you very much