Class 11 Exam > Class 11 Videos > Organic Chemsitry - R and S Configurations Made Easy
Organic Chemsitry - R and S Configurations Made Easy Video Lecture - Class 11
FAQs on Organic Chemsitry - R and S Configurations Made Easy Video Lecture - Class 11
| 1. How do you determine the R and S configurations in organic chemistry? |  |
Ans. In organic chemistry, the R and S configurations of chiral compounds are determined by assigning priorities to the substituents attached to the chiral center. This is done by using the Cahn-Ingold-Prelog priority rules, where the atoms with higher atomic number have higher priority. By assigning priorities and orienting the molecule in a specific way, the R configuration is assigned when the priorities decrease in a clockwise direction, and the S configuration is assigned when the priorities decrease in a counterclockwise direction.
| 2. What are the Cahn-Ingold-Prelog priority rules used for determining the R and S configurations? | |
Ans. The Cahn-Ingold-Prelog priority rules are used to determine the R and S configurations in organic chemistry. These rules assign priorities to the substituents attached to the chiral center based on the atomic number of the atoms directly bonded to the chiral center. The higher the atomic number, the higher the priority. If there is a tie in atomic numbers, the atoms directly bonded to the chiral center are compared until a difference is found. The molecule is then oriented in a specific way, and the R configuration is assigned when the priorities decrease in a clockwise direction, and the S configuration is assigned when the priorities decrease in a counterclockwise direction.
| 3. Can you give an example of determining the R and S configurations using the Cahn-Ingold-Prelog priority rules? | |
Ans. Certainly! Let's consider the compound 2-bromobutane. Assigning priorities to the substituents attached to the chiral center (the carbon with the bromine), we find that the bromine has the highest priority (atomic number 35), followed by the carbon bonded to three hydrogens (atomic number 6), and then the carbon bonded to two hydrogens and another carbon (atomic number 6). By orienting the molecule in a way that the lowest priority group (hydrogen) is pointing away from us, we can determine that the priorities decrease in a counterclockwise direction. Therefore, the configuration of this compound is S.
| 4. Are there any shortcuts or tricks to quickly determine the R and S configurations in organic chemistry? | |
Ans. Yes, there are a few shortcuts that can help determine the R and S configurations more easily. One of these shortcuts is the Fischer projection, which allows for a simplified representation of chiral compounds. By rotating the Fischer projection 90 degrees counterclockwise and assigning priorities to the substituents as usual, the R and S configurations can be determined more quickly. Additionally, using models or computer software can also aid in visualizing the molecule and determining its configuration.
| 5. Can the R and S configurations be changed by rotating the molecule? | |
Ans. No, the R and S configurations of a chiral molecule cannot be changed by simply rotating the molecule. The R and S configurations are determined by the spatial arrangement of the substituents around the chiral center, which remains the same regardless of the orientation or rotation of the molecule. However, it is important to note that interconverting enantiomers (mirror-image isomers) can result in a change in the R and S configurations, as the substituents are rearranged in a different spatial arrangement.
Text Transcript from Video
hi my name is Frank
er SC and this video is on RNs and what
to do it the different situation okay
yeah Arnaz freezing swiveling violence
curious what that means I'll show you
later okay so on the par to have the
four different situations that can
possibly have you can have your lowest
lowest priority group in the back that's
usually our most favorite that's what
you guys all not to do your lowest
priority moving from this one's a little
bit harder but be sure together baby not
to do that and then lowest priority
group on the slide bar on top this one
you guys might have a little trouble
doing and then okay so let's look at
this one first of all hope you guys
already know this but are just means
that the the priority moves to go
clockwise and then s this means that the
priority of groups from the lowest to
highest go counterclockwise
so rule number one the first thing you
do is you got to rank your your groups
so this Romijn is the highest and then
alcohol or means highest also because
it's just the biggest out of here that
comes with the oxygen but it's this
carbon here in the steep street and lots
of the hydrogen here so yeah so bronies
actually the highest even though this
one though you got a second
but highest second highest thirty nice
Louis so you go this is one two three
four that is counter clockwise so it is
this nice meeting next one your lowest
priority group let's just carry over the
the ratings so one two three four now
our lowest priority group is in the
front so we have a little problem now
you can't just do your normal our
testing so what I like to do myself is
just do it harness first so one skip
back to three our
so that's our but because your lowest
priority groups in the front it's not
our it's the opposite yes okay now you
guys might be a little confused by that
you're not just skip ahead a couple of
minutes I explain these two welcome
using ones but I show you this one so in
this one you're a wedge means it's
coming out at you so hydrogens this one
pro means two in the back because we're
two CH trees on top o ageism in the left
right so let's turn it so that the
lowest groups in the back so now you
have hydrogen in the back nice and easy
now your bromine is here so one two
three so this is s so see it works but
you just get the stuff before you got to
do this little foot thing Eames kind of
write down what you think it is it's not
opposite okay hope it helps next one
here this one is a little confusing and
this is actually a theory part and this
picky Beedrill here right the lowest
functional group for lowest function
loop is on the side a lot of times
people have this misconception that it
was on the side of the same thing you
just across how what you think it and
flip it it up cuz I do it I use a little
trick called freezin swivel I don't know
if you guys know the song teach me how
to dougie just think of the beat oh I'm
teaching either freeze and swivel freeze
and swivel so what you do is you
actually freeze this top loop here
because that guy doesn't you move at all
your goal is to move this hydrogen in
the back see you freeze and swivel it
reasons to a bullet and let me show you
so when you freeze and swivel it right
which means black marker
never mind ch street stays up there
because it's frozen and then you freeze
and swivel it
oho be in front okay so it was like this
before a ch3 on top alcohol or the front
loop in the back
Romina the front coming at you H on the
side this guy doesn't even move at all
because our goal is to get this cot in
the back to freeze and swivel it may be
freezin swivel it now bro means here
front coming after you and then in the
back and I could be your normal Arness
thing now so let's see after you
manipulated always been down your
priority priority ranking so 1 2 3 4 so
1 2 2 2 3 that's going counterclockwise
so that's s that's right sir okay and
the next one this one you saw the
violence so you could take out all your
rage you have a hydrogen and because our
goal right now is to get in the back so
you literally just punched a guy in the
face and then punch professional
hydrogen puncher here if you see
hydrogen ions how punch in the face
and then when you punch the hydrogen
face he's gonna fall to the back and let
me show you guys that
let's see ch3oh er is kind of in the
back okay so then you punch the hydrant
in the face then whatever was in the
front just came to the top whatever it
was in the back is not in the front let
me show you that again so you punch him
in the face
so then hydrogen falls back but it
wasn't friend came up I was in the back
or you can also think of it as reasons
wiggling it but you're freezing
the ch3oh amount is still chilly
watching all the action
okay so let's carry over our rankings
one two three four
Louis pooping in the back so we're good
these are our stuff one two three that's
counterclockwise counterclockwise is s
that's there you go that's your answer
all right if you want to see more
complicating examples we don't have
hydrogen you know as Louis grew watch my
next video
okay okay so this one here this is the
one complicated one because everyone's
some functional groups let's you can get
this so a positive video rank rank the
rank the different constituents from 1
to 4 1 being the highest for being
applause
okay all right so I don't know if you
did it right or not but the lowest well
the highest one is bromine this is the
biggest atom and it's fluorine and it's
the okay if you know this functional
group watch my functional group video
yeah this is a key oh hi so okay okay so
the reason why bromine is first because
when you rank them you go atom to atom
so the first time I'm here is actually a
carbon alright first time here is also a
carbon so they can't be the one or two
bromine is the biggest out of them here
so that's number one
then is for any of those floorings above
it in the periodic table and as you go
up you get smaller as you go to your
right get smaller as well but don't
worry about that
so why am - now you have to rank these
two right they both are attached to this
carbonyl thing carbonyl is just the
carbon with a double bond to an oxygen
right but so chief cos what you do is if
you look at what they're bonded to so
this is a carbon that's bonded to an
oxygen and because it is a double bond
be it's bonded to what we call a phantom
oxygen here I'm just going to put a
little star here no fancy and Bosnians
who is a carpet okay and this carbon
here is bonded to a
fans of carbon because it's a little one
I mean fans of oxygen and then an inch
so let's see who wins a lot of the
carbonyl in them that's why it's three
it's right it's a boy
okay alright so we have our one two
three four the lowest priority group is
you might want to pause your read it out
and try and get your RN s on your own
but
er SC and this video is on RNs and what
to do it the different situation okay
yeah Arnaz freezing swiveling violence
curious what that means I'll show you
later okay so on the par to have the
four different situations that can
possibly have you can have your lowest
lowest priority group in the back that's
usually our most favorite that's what
you guys all not to do your lowest
priority moving from this one's a little
bit harder but be sure together baby not
to do that and then lowest priority
group on the slide bar on top this one
you guys might have a little trouble
doing and then okay so let's look at
this one first of all hope you guys
already know this but are just means
that the the priority moves to go
clockwise and then s this means that the
priority of groups from the lowest to
highest go counterclockwise
so rule number one the first thing you
do is you got to rank your your groups
so this Romijn is the highest and then
alcohol or means highest also because
it's just the biggest out of here that
comes with the oxygen but it's this
carbon here in the steep street and lots
of the hydrogen here so yeah so bronies
actually the highest even though this
one though you got a second
but highest second highest thirty nice
Louis so you go this is one two three
four that is counter clockwise so it is
this nice meeting next one your lowest
priority group let's just carry over the
the ratings so one two three four now
our lowest priority group is in the
front so we have a little problem now
you can't just do your normal our
testing so what I like to do myself is
just do it harness first so one skip
back to three our
so that's our but because your lowest
priority groups in the front it's not
our it's the opposite yes okay now you
guys might be a little confused by that
you're not just skip ahead a couple of
minutes I explain these two welcome
using ones but I show you this one so in
this one you're a wedge means it's
coming out at you so hydrogens this one
pro means two in the back because we're
two CH trees on top o ageism in the left
right so let's turn it so that the
lowest groups in the back so now you
have hydrogen in the back nice and easy
now your bromine is here so one two
three so this is s so see it works but
you just get the stuff before you got to
do this little foot thing Eames kind of
write down what you think it is it's not
opposite okay hope it helps next one
here this one is a little confusing and
this is actually a theory part and this
picky Beedrill here right the lowest
functional group for lowest function
loop is on the side a lot of times
people have this misconception that it
was on the side of the same thing you
just across how what you think it and
flip it it up cuz I do it I use a little
trick called freezin swivel I don't know
if you guys know the song teach me how
to dougie just think of the beat oh I'm
teaching either freeze and swivel freeze
and swivel so what you do is you
actually freeze this top loop here
because that guy doesn't you move at all
your goal is to move this hydrogen in
the back see you freeze and swivel it
reasons to a bullet and let me show you
so when you freeze and swivel it right
which means black marker
never mind ch street stays up there
because it's frozen and then you freeze
and swivel it
oho be in front okay so it was like this
before a ch3 on top alcohol or the front
loop in the back
Romina the front coming at you H on the
side this guy doesn't even move at all
because our goal is to get this cot in
the back to freeze and swivel it may be
freezin swivel it now bro means here
front coming after you and then in the
back and I could be your normal Arness
thing now so let's see after you
manipulated always been down your
priority priority ranking so 1 2 3 4 so
1 2 2 2 3 that's going counterclockwise
so that's s that's right sir okay and
the next one this one you saw the
violence so you could take out all your
rage you have a hydrogen and because our
goal right now is to get in the back so
you literally just punched a guy in the
face and then punch professional
hydrogen puncher here if you see
hydrogen ions how punch in the face
and then when you punch the hydrogen
face he's gonna fall to the back and let
me show you guys that
let's see ch3oh er is kind of in the
back okay so then you punch the hydrant
in the face then whatever was in the
front just came to the top whatever it
was in the back is not in the front let
me show you that again so you punch him
in the face
so then hydrogen falls back but it
wasn't friend came up I was in the back
or you can also think of it as reasons
wiggling it but you're freezing
the ch3oh amount is still chilly
watching all the action
okay so let's carry over our rankings
one two three four
Louis pooping in the back so we're good
these are our stuff one two three that's
counterclockwise counterclockwise is s
that's there you go that's your answer
all right if you want to see more
complicating examples we don't have
hydrogen you know as Louis grew watch my
next video
okay okay so this one here this is the
one complicated one because everyone's
some functional groups let's you can get
this so a positive video rank rank the
rank the different constituents from 1
to 4 1 being the highest for being
applause
okay all right so I don't know if you
did it right or not but the lowest well
the highest one is bromine this is the
biggest atom and it's fluorine and it's
the okay if you know this functional
group watch my functional group video
yeah this is a key oh hi so okay okay so
the reason why bromine is first because
when you rank them you go atom to atom
so the first time I'm here is actually a
carbon alright first time here is also a
carbon so they can't be the one or two
bromine is the biggest out of them here
so that's number one
then is for any of those floorings above
it in the periodic table and as you go
up you get smaller as you go to your
right get smaller as well but don't
worry about that
so why am - now you have to rank these
two right they both are attached to this
carbonyl thing carbonyl is just the
carbon with a double bond to an oxygen
right but so chief cos what you do is if
you look at what they're bonded to so
this is a carbon that's bonded to an
oxygen and because it is a double bond
be it's bonded to what we call a phantom
oxygen here I'm just going to put a
little star here no fancy and Bosnians
who is a carpet okay and this carbon
here is bonded to a
fans of carbon because it's a little one
I mean fans of oxygen and then an inch
so let's see who wins a lot of the
carbonyl in them that's why it's three
it's right it's a boy
okay alright so we have our one two
three four the lowest priority group is
you might want to pause your read it out
and try and get your RN s on your own
but
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Oct 01, 2025
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