Hey guys, Professor Dave here, I wanna talk to you about stereoisomers
Hey guys, Professor Dave here, I wanna talk to you about stereoisomers

especially enantiomers and diastereomers.
especially enantiomers and diastereomers.

so we're probably familiar with the term isomerism
so we're probably familiar with the term isomerism

and understand a little bit about what isomers are, but there's different kinds
and understand a little bit about what isomers are, but there's different kinds

and we may recall what structural isomers are
and we may recall what structural isomers are

structural isomers are molecules that contain
structural isomers are molecules that contain

the same molecular formula but differ in connectivity
the same molecular formula but differ in connectivity

in other words the same number of the same types of atoms but connected differently
in other words the same number of the same types of atoms but connected differently

so here's an example of two different butanes
so here's an example of two different butanes

we have straight chain butane and isobutane, they're both
we have straight chain butane and isobutane, they're both

C4H10 but they're connected differently
C4H10 but they're connected differently

as opposed to the straight chain of these carbons has been moved over to
as opposed to the straight chain of these carbons has been moved over to

the middle
the middle

so those are structural isomers. now stereoisomers
so those are structural isomers. now stereoisomers

are compounds that have the same molecular formula
are compounds that have the same molecular formula

and the same connectivity, in other words the same
and the same connectivity, in other words the same

atoms connected in the same way however
atoms connected in the same way however

they differ in the way they are oriented in three-dimensional space
they differ in the way they are oriented in three-dimensional space

so something like this, we can see that it is the same
so something like this, we can see that it is the same

atoms bound in the same manner however
atoms bound in the same manner however

they differ in the way that they are or oriented in three-dimensional space
they differ in the way that they are or oriented in three-dimensional space

and let's talk a little bit about why
and let's talk a little bit about why

so the first kind of stereoisomeric relationship I want to talk about
so the first kind of stereoisomeric relationship I want to talk about

involves molecules that are called enantiomers
involves molecules that are called enantiomers

of one another. enantiomers are molecules
of one another. enantiomers are molecules

that are non-superposable mirror images of each other
that are non-superposable mirror images of each other

in other words they are stereoisomers so they have the same connectivity
in other words they are stereoisomers so they have the same connectivity

but if you take the mirror image of one of the compounds
but if you take the mirror image of one of the compounds

you get the other and they're not the same because they do not
you get the other and they're not the same because they do not

overlap precisely the same way in three-dimensional space
overlap precisely the same way in three-dimensional space

so take for an analogy our hands so
so take for an analogy our hands so

here's one of my hands and the mirror image of this hand
here's one of my hands and the mirror image of this hand

is my other hand, so these have an
is my other hand, so these have an

enantiomeric relationship in the sense that they are mirror images
enantiomeric relationship in the sense that they are mirror images

of one another but they do not precisely overlap, I'm not going to be able to get
of one another but they do not precisely overlap, I'm not going to be able to get

every finger to overlap
every finger to overlap

its corresponding finger properly so
its corresponding finger properly so

they have an enantiomeric relationship because they
they have an enantiomeric relationship because they

are non-superposable mirror images of one another. and we can come up with all
are non-superposable mirror images of one another. and we can come up with all

kinds of macroscopic examples of this
kinds of macroscopic examples of this

but molecules are doing the same thing so
but molecules are doing the same thing so

let's take something like this molecule and let's reflect it across
let's take something like this molecule and let's reflect it across

a mirror plane here
a mirror plane here

and we can all agree that this is the mirror image of that
and we can all agree that this is the mirror image of that

so we have X, whatever these atoms are, doesn't matter
so we have X, whatever these atoms are, doesn't matter

X and then the Y and then the Z, these are
X and then the Y and then the Z, these are

mirror images of one another but now if we rotate the resulting mirror image
mirror images of one another but now if we rotate the resulting mirror image

to try to place it on top of the original
to try to place it on top of the original

in order to do that if we want the X to line up we're just gonna twist this
in order to do that if we want the X to line up we're just gonna twist this

like a top 180 degrees
like a top 180 degrees

and we would get this but the problem is if we tried to take this and put it on top of that
and we would get this but the problem is if we tried to take this and put it on top of that

not all of the atoms are gonna overlap properly
not all of the atoms are gonna overlap properly

the W. the central atom and the X, those would overlap just fine
the W. the central atom and the X, those would overlap just fine

but you'd find that the Y would be on top the Z and the Z
but you'd find that the Y would be on top the Z and the Z

would be on top at the Y, therefore
would be on top at the Y, therefore

this molecule and its mirror image which are two
this molecule and its mirror image which are two

distinctly different molecules are
distinctly different molecules are

enantiomers of one another because they are non superposable
enantiomers of one another because they are non superposable

mirror images of one another
mirror images of one another

so molecules that have an enantiomer
so molecules that have an enantiomer

display a quality called chirality
display a quality called chirality

this is something that we would typically assigned to a carbon
this is something that we would typically assigned to a carbon

that has four different substituents projecting from it
that has four different substituents projecting from it

so for example in the top this carbon atom has a bromine atom
so for example in the top this carbon atom has a bromine atom

the implied hydrogen, and two identical
the implied hydrogen, and two identical

methyl groups, so we would not regard this
methyl groups, so we would not regard this

as chiral, because it has two identical methyl groups
as chiral, because it has two identical methyl groups

so it does not have four distinctly different substituents
so it does not have four distinctly different substituents

now this would mean that this does not have
now this would mean that this does not have

an enantiomer because if you made the mirror image of this molecule
an enantiomer because if you made the mirror image of this molecule

it would be precisely the same molecule, it would be superposable
it would be precisely the same molecule, it would be superposable

so it would not have an enantiomer, its mirror image would be identical
so it would not have an enantiomer, its mirror image would be identical

and it is therefore not chiral. however
and it is therefore not chiral. however

this molecule is chiral because this carbon
this molecule is chiral because this carbon

has a bromine atom, the implied hydrogen
has a bromine atom, the implied hydrogen

this one carbon chain, and then a two carbon chain so
this one carbon chain, and then a two carbon chain so

that is four distinctly different groups
that is four distinctly different groups

and if we went and took the mirror image we would see
and if we went and took the mirror image we would see

that it is that, and now if we try to flip that around
that it is that, and now if we try to flip that around

we would get the same structure but now
we would get the same structure but now

the bromine would be on the dash bond because if
the bromine would be on the dash bond because if

the bromine atom is on the wedge bond
the bromine atom is on the wedge bond

out of the board like this, if we flip the whole thing 180
out of the board like this, if we flip the whole thing 180

now the bromine is gonna be going into the board, so if we try to place this on
now the bromine is gonna be going into the board, so if we try to place this on

top of that molecule
top of that molecule

it is not gonna line up properly so therefore this molecule
it is not gonna line up properly so therefore this molecule

is chiral, it has a chiral center
is chiral, it has a chiral center

or center of chirality or stereogenic center
or center of chirality or stereogenic center

all terms that mean the same thing and therefore it does
all terms that mean the same thing and therefore it does

have an enantiomer. likewise over here
have an enantiomer. likewise over here

this is a carbon with four different groups, this is a similar molecule
this is a carbon with four different groups, this is a similar molecule

but two of the groups are the same, we have two fluorine atoms
but two of the groups are the same, we have two fluorine atoms

so if you at home wanna go ahead and check you could
so if you at home wanna go ahead and check you could

draw the mirror images of both these compounds
draw the mirror images of both these compounds

and you could see that this is chiral
and you could see that this is chiral

because there is no way to rotate its mirror image
because there is no way to rotate its mirror image

so as to place it upon the original and have it line up flawlessly
so as to place it upon the original and have it line up flawlessly

however this one over here, having two identical fluorine atoms
however this one over here, having two identical fluorine atoms

if you drew the mirror image of this molecule there is a way that you could
if you drew the mirror image of this molecule there is a way that you could

rotate it
rotate it

so as to make it flawlessly superposable
so as to make it flawlessly superposable

therefore this cannot be chiral, this is
therefore this cannot be chiral, this is

achiral, meaning a prefix
achiral, meaning a prefix

that implies not so this is not chiral.
that implies not so this is not chiral.

it does not have a mirror image that is
it does not have a mirror image that is

distinctly different from the original.
distinctly different from the original.

thanks for watching, guys. subscribe to my channel for more tutorials
thanks for watching, guys. subscribe to my channel for more tutorials

and as always feel free to email me with questions
and as always feel free to email me with questions