Isomerism - Organic Chemsitry Video Lecture - Class 11

do you know how I am seeing all these
beautiful objects well the reason lies
in chemistry our vision requires a
protein called rhodopsin rhodopsin has a
small helper molecule sis 11 retinol
which is made from vitamin A an
important phenomenon occurs on sis 11
retinol because of which we can see the
beautiful world around us what is it
let's find out in today's episode
hello everybody I am the oh brother
Goswami and I warmly welcome you to the
colorful world of chemistry today we
will study a phenomenon that is found
all around us and yet is so unique that
it can help us see yes I am talking
about isomerism in today's episode we
will study what isomerism is and the
different types of isomerism that is
structural isomerism and stereoisomerism
finally we will look at ways and means
to crack your exams in exam decoded
let's start our journey today with
isomerism what is isomerism well the
word isomerism is derived from the Greek
word ISOs which means equal and mirrors
which means part so it refers to
bilateral similarity if not equivalence
of structures it was a term coined by
Swedish scientists jöns jakob berzelius
but what exactly does isomerism mean
isomerism is the phenomenon of existence
of two or more compounds having the same
molecular formula but different
properties and compounds like these are
called isomers isomerism can be broadly
classified into two categories as
structural isomerism and stereoisomerism
so let's take structural isomerism first
structural isomers are molecules which
have the same molecular formula but
different structures basically the
structural arrangement of their atoms is
different and this phenomenon is called
structural isomerism structural
isomerism is further classified into
four types chain isomerism position
isomerism functional group isomerism and
metamerism let's start with chain isomer
so let us take the example of butane it
is an alkane with four carbons and 10
hydrogens now if I try and arrange the
carbon and hydrogen atoms to structural
arrangements are possible
this first one has carbons arranged in a
straight chain and has a name n butane
the second one has three carbons
arranged in a straight chain and one
carbon as a branch on the second carbon
this is known as
isobutane for these compounds have the
same molecular formula c4h10 but
different carbon skeletons such
compounds are called
chain isomers the second type of
structural isomerism is a position
isomerism in this type of isomerism two
or more compounds differ in the position
of substituent atoms of functional
groups on the carbon skeleton the
molecular formula remains the same such
isomers have the same carbon skeleton
let us take the example of bromo propane
we know that there are three carbon
atoms in propane
now there are two positions of carbons
on which the functional group the bromo
group can attach either on the first
carbon or on to the second carbon
if bromo group is attached to the first
carbon it is called one bromo propane
and if bromo group is attached to the
second carbon
it is called 2-bromo propane so we can
say that there are two position isomers
with the molecular formula c3h7 Br
now the third type of structural
isomerism is functional group isomerism
as the name suggests in this type of
isomerism the isomers contain different
functional groups but remember the
molecular formula remains the same
for example a compound with molecular
formula c3 h6 o2 as 2 functional group
isomers propanoic acid in which the
functional group is a carboxylic acid
and ethyl ethanoate in which the
functional group is an ester the last
type of structural isomerism that we
will study is metamerism metamerism
arises due to different alkyl chains on
either side of the functional group in
the molecule let's take an example to
illustrate this the compound with the
molecular formula c4 h 11n shows
metamerism
the first isomer has two ethyl groups on
each side of NH in the second isomer
there is a methyl group on one side and
a propyl group on the other side of
enemy
thus metamerism arises due to different
alkyl chain on either side of the
functional group in the molecule I think
now it's time to take a break so that
you can digest the different types of
structural isomers but before going I
want you to think about this question
what are the functional groups which
show metamerism you can search the
answer on ww2 Palani calm or just wait
for me to come back
welcome back
this is debobroto Goswami and you are
watching chemistry 11 before the break I
had asked you what are the functional
groups which show metamerism I hope you
try to look up the answer but anyways
here it is metamerism is shown my
functional groups na o s or C double
bond o group let's move on now I want to
introduce you to the other kind of
isomerism that is stereoisomerism in
stereoisomerism the compounds have the
same constitution and sequence of
covalent bonds which is unlike
structural isomerism but they differ in
relative positions of their atoms or
groups in space let's discuss it in
detail there are two types of
stereoisomerism namely geometry two
isomerism and optical isomerism let's
begin with geometrical isomers ISM
geometrical isomerism arises because of
different spatial arrangement of atoms
this happens because of the restricted
rotation of the carbon-carbon double
bond but geometrical isomers 'm can also
arise from ring structures where the
rotation of bonds is greatly restricted
molecules exhibiting geometrical isomers
'm are called geometrical isomers let's
take the example of butte 2 in to
understand geometrical isomerism this
molecule has a double bond between the
second and third carbon due to this
double bond there will be restricted
rotation in the
around the second and third carbon and
there will be two different arrangements
of atoms or groups in space
when the two identical groups are
present on the same side of the double
bond
the isomer is referred to as a sis I
summer in Butte - in the structure in
which the two methyl groups are on the
same side of the double bond is named as
sis Butte - in but what if the two
methyl groups are present on the
opposite sides of the double bond such a
structure is referred to as trans beauty
so in general when two identical groups
are present on the opposite sides of the
double bond
the isomer is referred to as trans
isomer geometric isomerism is also
called as cysts trans isomer ISM we have
a caller with us let us clarify a doubt
hello sir my name is ash on my question
is though alkyne have a triple bond do
they also show since trans isomerism
well this is a nice question the answer
is no alkynes do not show sis trans
isomer ISM I will tell you why this is
because alkynes have a triple bond so
alkynes are linear and there will be no
restricted rotation and different
arrangement of substituent's of atoms
and groups in space is not possible
remember that in the beginning of the
show we talked about sis 11 retinol
which helps in vision this is converted
to trance retinol when exposed to light
therefore the light energy is absorbed
during the conversion of isomers of
retinol it is then given off to the
protein and transported through the
visual system to enable us to see this
shows how significant geometric
isomerism is let us now move on to
optical isomerism but before that we
must know what optical activity is we
know that light is made up of
electromagnetic waves vibrating in all
directions such a light is called a non
polarized light or unpolarized light
when this unpolarized light is passed
through Nicole prism we get plane
polarized light plane polarized light is
defined as the light which oscillates in
only one way
there are certain substances which
rotate the plane polarized light such
substances are called optically active
substances when a substance rotates the
plane of polarized light in the
clockwise direction it is named
dextrorotatory or the +4 and when a
substance rotates the plane of polarized
light in anti-clockwise direction it is
called levorotatory or the - ball well
that's all for today now it's time for a
short break but stay tuned because
coming up after the break is the segment
which will show you how to put all this
knowledge to good use
yes I'll be back with exam decoded after
this break but as you know chemistry
fundas are just a click away
I mean you can always log on to
www.wymt.com
welcome back to chemistry I am do Britta
Goswami and today we are talking about
isomerism before the break I had asked
you who discovered and developed the
first prism that produced plane
polarized light well the answer is
William Nicol he developed the first
prism that produced plane polarized
light and now it's time to test your
knowledge but before we do that let's do
a quick recap of all that we have
learned today in this episode we studied
the phenomenon of isomerism to define it
the existence of two or more compounds
with the same molecular formula but
different properties is known as
isomerism the phenomenon in which
molecules have same molecular formula
but different structural arrangements of
the atoms is called structural isomerism
the phenomenon in which compounds have
the same constitution and sequence of
covalent bonds but differ in relative
positions of their atoms or groups in
space is called stereoisomerism now that
we have refreshed our learnings let's go
on to exam decoded
welcome to exam decoded before I give
you some important tips on today's
episode let's play our usual rapid-fire
round the rules are the same as always
I will ask you five questions and you
must answer each question in less than
five seconds you will get one mark for
each correct answer and I will help you
interpret your total with our special
topper scorecard so let's begin here is
your first question
sis trans isomer ISM is also called a
optical isomerism finished functional
isomerism C positional isomerism the
geometrical isomerism
the answer is d sis trans isomerism is
also called geometrical isomerism
question 2 in butane and isobutane are
which kind of isomers
geometrical meta mers-free
chain the position the answer is C they
are chain isomers as n-butane is
straight chain and isobutane is branched
the third question the isomers in which
the two identical groups are present on
the same side of the double bond
jane isomers beach position isomers see
trans isomer be sis isomer the answer is
d CI soman ii last question metabolism
arises due to different alkyl chains on
either side of the functional group in
the molecule true or false
well the answer is true and now the last
one bromo propane and to bromo propane
are chain isomers true or false
well the answer is false they are
position isomers and now for the scores
compare your total with our scorecard
and see where you fit if you have scored
cool maps then you are a high flyer and
can rest assured that your preparation
is going well if you have scored four or
three then you are an achiever you need
just a bit more revision of sample
questions if you have scored less than
three then you need help with the basic
concepts of this topic you can get this
help on www.tehurn.com majinkappa comes
under the unit
organic chemistry basic principles and
techniques it has a weight age of seven
marks which makes it a critical unit to
focus on the questions asked from this
topic can be very short answer type
questions for one mark and short answer
type questions for two or three months
these questions pertain to knowledge
ability here is a to mark question to
brush up your concepts about this topic
identify the type of isomerism
that exists between the given molecules
take a look at the first set of
molecules on your screen you can see
that both structures have the same
molecular formula C 5 H then o the first
structure represents a ketone namely 3
pentanone and the second structure
represents an aldehyde that is one
fentanyl
since these two isomers have different
functional groups they exhibit
functional group isomerism this
information will fetch you one month now
for the second part you can see that the
two structures have the same molecular
formula now the next step is to identify
the type of isomerism
the two given structures have the same
functional group that is ether but they
have different alkyl chains on either
side of the functional group in the
molecule so these two isomers are meta
Murs and exhibit metamerism this will
fetch you the remaining mark
well it's time to say goodbye but I will
leave you with some food for thought how
can the concept of optical rotation be
used to measure sugar concentration in
sugar industry confused don't be just
keep thinking and you will come up with
the answer
for more help you can always log onto
www.koco.com till then it's devavrata
wishing you a well-structured
preparation