Chemical Reactions of Haloarenes Video Lecture | Chemistry for JEE Main & Advanced

hello friends this video on haloalkanes
and hello arenas part 27 is brought to
you by exam fear calm no more fear from
exam now I'll talk about the reactions
of hello alkanes with metals they form
something called organometallic
compounds you see most of the organic
chlorides there is a bromide or iodide
these three actually not the fluorides
they react with some metals to give
chemical metal bonds is called organic
organometallic compounds is something
like this rmgx pair accelerates like a
negative charge
mmm this will get slightly positive
charge and gets like an H it is very
very polar it's highly polar so if you
see these rmgx nothing but the grignard
reagent in my in time event by victor
regardless it is a very critical region
we have choose this region in class xi
also then we have form these kinds of
reactions addition reaction so this is
my grignard reagent and this is our mg x
so this is my al-qaida light our via
react with magnesium in business them to
either you get r mg x correct and you
see the carbon magnesium on here if you
see is covalent but it's highly highly
polar it's very very cool and these are
very reactive they are very reactive and
they react with even small amount of
proton give hydrocarbon the reaction
goes like this if i've rmgx this reactor
you react with water it gives rh plus mg
which is very reactive and that's why it
has to be it has to be free from
moisture it has to be free from moisture
so even a small amount of moisture that
is water it will react very reactive
substance
highly highly polar so there are two
things about this highly polar
and they're very reactive they
automatically come on and they have used
as a reagent in law of chemical
reactions now we'll start with hello
greens let's talk about the chemical
properties of Hillary's we'll talk about
a nucleophilic substitution we talked
about eliminations and we'll talk about
the reaction with metals similar to
hello alkies talk about these things for
hello Ahri's now please know we are
talking about
hello arraigns no not hello alkenes okay
something like this would be talking
about things like this means with
chlorine remember the chlorobenzene
we'll talk about these kind of compounds
first we'll talk about the DQ
nucleophilic substitution reaction see
for new view feeling substitution
reaction the one which attacks is
nucleophile right the nucleophile
always looks for positive charge
correct correct
also if CX bond it has to break CX bond
but in this case of Halloween the CX
bond is very strong and thus the
nucleophilic substitution is not easy it
is less reactive it is not easy
right so if you take arrive halides so
they are not very much reactive towards
nucleophilic secretion yeah and the
reasons are for the resonance effect the
sp3 hybridized carbon in CX bond
instability of finalcut time and the
repulsion we'll talk about all these
four effects due to which you will see
that the iron halides are not very much
flown to nucleophilic substitution yeah
so we'll see that due to resonance
effect the our hello arraigns
will acquire a partial double bond the
CX bond which we have right the partial
double bond and that's why it's
difficult to break this bond we will see
that let us take this chlorobenzene for
example it's let's suppose this is my
chlorobenzene chlorine with the
electrons here so now what will happen
as this chlorine will give some electron
to this guy
move in this direction so what you will
get a new structure will you make is
chlorine with a double bond the positive
charge and a negative charge comes here
mean if charge comes here and this is my
ball in 2 more actually this one can
also shift in this direction so with
that what you depth is showing the
double bond again with positive charge
you'll form a bond here and the negative
charge will come here negative charge
will come here and it's in the bond you
draw more resonating structure for this
and this will be again the closed me the
positive charge and this bond will shift
in this direction you'll get a bond here
and here and here you get a negative
charge you see there so many resonating
structure right so with this they are
two things which you notice first thing
is that CX bond is double bond right so
it's difficult to break correct
so difficult to break first thing is
what if you can do break CX bond why
because of partial partial double bond
and the second thing is that due to
resonance this this reactant is stable
reactant is stable due to resonance
since this reactant is stable to do
resonance slant have extra urge to react
correct
so with the resonance effect we can
explain that the nucleophilic
substitution is difficult so yeah what
you'll sn1 or - whatever you want is
difficult correct so we have seen the
resonance plays a role to explain why
nucleophilic substitution is difficult
in case of hollow earrings now I'll try
to explain why nucleophilic substitution
is difficult because of sp2
hybridization if you see any hello
alkane you pick hello and clean let's
suppose this is V a ch3 ch2
and it suppose CL this is a hello alkane
and let's take one hello Karim
let's take chlorobenzene once again so
if you see this carve and these are this
is my hero garb and this is my hero
carbon here this carbon it is 1 2 3 4
that is sp3 hybridised see this carbon 1
2 3 that is sp2 hybrid right so the hero
carbon here is sp3 hybridized here this
sp2 hybridized sp2 hybridized means more
percentage s character like more
percentage s character then that means
it is more electronegative so that means
if I compare these two carbon let's
suppose this carbon is carbon 1 and this
carbon is it suppose carbon 2 here so
carbon 2 is more electronegative then
carbon 1 why because carbon 2 is sp2
hybridized more percentage s character
so it is more electronegative cut it can
hold it can hold it can hold the halogen
tightly that means CX gon will be
stronger so in case if you see the CX
bond in hello alkene if you see that is
177 picometer there is a length but the
same CX bond length in hello arena if
you see is less 169 Pico meter that
means this is more stable more strong
right this is strong bond very strong
bond is difficult to break and we know
that for a substitution it is mandated
to break the bond seeing's bond breakage
is mandatory so this bond is strong it
will be difficult to break the bond a
does the nucleophilic solution will be
difficult in case of hollow Ares based
on this parameter that is it is sp2
hybridized
now let's see the unstable cation thing
so let's assume that you have this hello
chlorobenzene and you somehow managed to
remove the halogen this becomes positive
charge now if this becomes positive
charge if you see you can't create a
resonating structure correct but in this
case of let's suppose chlorobenzene you
have seen that you were able to create
resonating structure okay so now since
you are not able to create resonance
structure that means this is unstable
and this is stable so it will not like
to go into unstable state so cation
formation also is difficult because the
cation is unstable so sn1 is totally you
know totally ruled out sn2 possibility
is there but again if you see this
carbon is totally sterically hindered
right difficult there is no space less
space so and same to it also is
difficult so I said to is Hospice like
you but if you can sn2 is sn1 is totally
ruled out because for sn1 reaction could
happen the carbo cation comeback
formation is mandatory but here we see
the carbo cation itself is very very
unstable as you compare to the porzel
reactant so carbo cation won't be oh
let's see the fourth one the repulsion
see if you see this guy
so the nucleophiles are what
nucleophiles are they themselves are the
one which loves nucleus that means they
are electron rich correct so if you see
the EU like typical example is CN minus
o h - right
these are my nucleophile CL minus VR
minus Emin
googly eyes they are electron-rich but
if you see holloa rains they are also
electron-rich
you see fellow rains are also electron
which if hello aleene's arrange our
electron rich nucleophiles electron
which there will be repulsion between
them because as I told like repels life
right positive attracts negative but
positive repel positive negative repel
negative right this you have seen you
know electrostatic force of attraction
same charged repel a up with a
chance attract either so hello Aries
itself has electron raise nucleophiles
electron range so they will repel each
other
correct so that is also one reason why
nucleophilic substitution difficult in
so let's talk about a different kind of
reaction will talk about in calories so
what we have to hold till noise hello
razor it's difficult do both or as
nucleophilic reactions why we don't
worse this is more electron rich right
so what if we can add some electron
withdrawing group example no.2 this no.2
will withdraw electron so this will
become electron rich 2 electron pool so
in that case nucleophilic reactions is
possible so we will see those kind of
thing where will try to have a reactions
and hello rings they will fight will try
to add some electron withdrawing groups
we should make it more compliant for
nucleophilic submission reactions in
this case we will see the replacement
top halogen Yoh rope you'll also see
electrophilic suppression reaction as I
told these are electron rich so it can
go for electrophilic solution reaction
in that case we'll talk about
halogenation nitration sulfonation
friedel-crafts reaction you will also
see reactions with metal that is with to
see to that the reaction routes critic
reaction and fatigue leadership so let's
start the first one where we are saying
that we will have a nucleophilic sn2
action and we'll replace X by H so they
don't the nucleophilic substitution for
a hello and is difficult so this happens
only at drastic conditions so we'll see
this reaction will have a chlorobenzene
here this reaction is
chlorobenzene and a drastic condition
allowed this NaOH and then I shall give
a very strong base wish - right and then
it's H - is a very strong nucleophile
actually at 6:23 Kelvin high temperature
high pressure and we will give a H+
division with this you get OS here this
CN we will replace by
Oh H this is what happens this happens
the very drastic condition right you
have to increase the pressure increase
the temperature and then you get fin all
here from chlorobenzene so let's see
this reaction mechanism is sn2 reaction
let's see the mechanism so I have a
chlorobenzene here it controls
chlorobenzene this is my chlorobenzene
and on this my OS - is a nucleophile
that attacked this particular carbon
correct because this is my carbon on
which i have a good living rupa tasks
lee is a good leaving group now with
this what will happen is this carbon
atom this will get a negative charge
here right should to common the negative
charge this bond will break because see
this carbon also has on hydrogen here
correct now if my OS is also added so if
you see this this hydrogen here right so
it will be what you see the bonds here
will be H bond there is CA there is a
hydrogen
number a bond is 1 2 3 4 5 carbon is
straight repair and it can have 5 bond
so this bond will break and negative
charge will come here so with this what
you will get it this is a very slow step
so what you get is this compound with a
negative charge here and this is my
compound with h and CM and OHA correct
now if you see this particular carbon is
my tetravalent and this is my cap on and
if you see this is resonance stabilized
you can draw more resonating structure
for this this compound actually this
negative charge will go here single
negative the wave on here B H CL and H
you can have a mole shift in this
direction so what will happen here is
this will become a negative charge
positive negative form of bond bond and
this is H CL n so this is stable
actually because it has no so many
reason in structure right so now this
happens in the same together actually
but this ring structure is stable I am
telling you so this chlorine will leave
because pouring is a leaving grief this
chlorine will leave right and this
positive Shahi come here positive and
negative L form a bond so that what you
get is this
Gilbert H when this is nothing but a
phenol this is a fast step correctly sn2
there was no carbo cation form this OS
attack from behind and explain this CL
out correctly thank you visit exam
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