CBSE Class 12 > Class 12 Videos > Substitution SN2 Reaction (Part - 19) - Haloalkanes & Haloarenes, Chemistry, Class 12
Substitution SN2 Reaction (Part - 19) - Haloalkanes & Haloarenes, Chemistry,
FAQs on Substitution SN2 Reaction (Part - 19) - Haloalkanes & Haloarenes, Chemistry, Class 12
| 1. What is an SN2 reaction? |  |
Ans. An SN2 reaction, also known as a substitution nucleophilic bimolecular reaction, is a type of organic reaction in which a nucleophile replaces a leaving group on a carbon atom. It involves a concerted mechanism where the nucleophile attacks the carbon atom while the leaving group is simultaneously expelled.
| 2. What is the difference between haloalkanes and haloarenes? | |
Ans. Haloalkanes are organic compounds that contain halogen atoms (such as chlorine, bromine, or iodine) attached to an alkyl group. On the other hand, haloarenes are organic compounds that contain halogen atoms attached to an aromatic ring, such as benzene. The main difference lies in the structure, where haloalkanes have an alkyl group attached to the halogen, while haloarenes have an aromatic ring.
| 3. How does an SN2 reaction occur in haloalkanes and haloarenes? | |
Ans. In haloalkanes, an SN2 reaction occurs when a nucleophile attacks the carbon atom attached to the halogen, causing the halogen to leave as a leaving group. This leads to the substitution of the halogen atom with the nucleophile. In haloarenes, an SN2 reaction is less likely to occur due to the presence of an aromatic ring. The reaction is hindered by the stability of the aromatic system. Instead, haloarenes undergo different substitution reactions, such as SN1 or SNAr (nucleophilic aromatic substitution).
| 4. What factors influence the rate of an SN2 reaction in haloalkanes? | |
Ans. Several factors influence the rate of an SN2 reaction in haloalkanes. These include the nature of the alkyl or aryl group attached to the carbon atom, the strength of the nucleophile, the leaving group ability of the halogen, and the steric hindrance around the reacting carbon atom. Additionally, solvent polarity and temperature can also affect the reaction rate.
| 5. Can an SN2 reaction occur in haloarenes? | |
Ans. The occurrence of an SN2 reaction in haloarenes is relatively rare due to the stability of the aromatic system. The presence of an aromatic ring hinders the nucleophilic attack on the carbon atom, making it difficult for the reaction to proceed via an SN2 mechanism. Instead, haloarenes are more likely to undergo substitution reactions such as SN1 or SNAr (nucleophilic aromatic substitution).
Text Transcript from Video
hello friends this video on haloalkanes
in hilarious part 19 is brought to you
by exam flare calm no more fear from
exam let's talk about sn2 reaction let's
see the concept of us into reaction
there is a leaving group I mean there's
a compound here the leaving group air
and there is a very strong nucleophile
here this is a very strong nucleophile
this nucleophile can influence this atom
to move right in this nucleophile you
see can influence this atom to move and
this atom will have to move so in this
case the influence of this atom matters
also if you see there is no security
guards here right so no security guard
so had there been security guard this
lady would happen could not happen in to
influence this atom to go right there is
no security guard there is a strong
nucleophile this lady was strong these
things favors sn2 reaction so I have
someone who is very strong it comes it
influence kicks the person outs that is
sn2 reaction why it is sn2 reaction
because this is my mom
so the radiator manufacturers region
both to write both the strength of these
two besides what is the rate correct the
rate depends also on the reactant and
the nuclear so if you see this is a
typical example of sn2 reaction so this
was a reactant and this is my
nucleophile nucleophile is strong it
came and attack this guy from this side
see we see there was no security guard
no security hindrance now since this is
attacked this is the weak guy this is a
weak guy it left see the reaction is one
step back is all things happen one step
but the rate of the reaction depends on
two people right so it is sn2 reaction
these are the concept let's see the
reaction actually right
so in this case a lone pair of
nucleophile attacks the carbon
electrophilic carbon from the backside
please note backside is critical here
always the attack is from the backside
right and this expel another group this
is a leaving group so this nucleophile
attack this carbon this is a carbon from
the backside and like spin the living
room the blue one is the living room
right and this is one step this is one
set and thus since that is from the
backside it causes inversion will talk
about inversion in the next few slides
because see if you see is OS - hairs and
this hair if you see only one if I group
and two hydrogen so the space is there
for this - to attack right to security
goddess last only one security guard
actually so it can attack now there's a
transition stage it happens right and
then this voice - is linked and BR -
quito this is one step all one step but
sn2 why sin do because the slowest step
is my slowest step it is my slowest step
it involves two thing right this
involved two species one is the reactant
and one is a reagent so it is called sn2
it is by molecular nucleophilic
substitution reaction correct and
experimental it has been seen that the
rate of reaction depends both on the
reactant product so what they have done
is they have increase the reactants and
they have seen the rate of reaction
increase their increase the product
sorry they have increased the
nucleophile they have seen the rate of
reaction trees they have increase both
and they have seen the rate of in
reaction increases or means the rate of
reaction depends both on my reactants
and the nucleophile correct it is
attacked from back so there is something
called inversion because it's a diving
attack your back and we'll discuss more
about inversion in the next few slides
let's understand more about this
reaction
a protic solvent favors this why because
hey if this is a protic solvent coating
sulfonyl dawat if there is a halogen X
it is a halogen X let's suppose can
write this since this is a protic
solvent floating selim will try to
attract this halogen and will try to say
this halogen to leave on its own and
then it will become sn1 reaction because
if this halogen leaves on its own and
then some other Nick LaFollette is
attacking this becomes n1 reaction but
we don't want that we want someone to
attack from back for sn2 reactions so in
this case if it is a protic solvent it
is better so in that case there is no
what you call interface or there is no
disturbance or for these halogens there
is no extra reason or extra affinity of
these halogen to leave this particular
react
correct in this case there is no
intermediate form in sn1 you Eocene the
Cabo Verde Islands form in this case the
low intermediate form is all one step
process all one step process right and
in this case both subtract and attacking
legend they decide the rate of reaction
that's why it's called sn2 because there
are two species that decides the rate of
the reaction in this case a strong
nucleophile is too dry because i'm
saying to the nucleophile is attacking
right so that means the nucleophile
should be strong enough to attack to
kick this leaving rubout so if the
nucleophile is strong it is
added advantage inversion of control
takes place as I told explain what is
inversion of control in the next few
slides presence of bulky group near the
carbon atom has inhibiting effect for
example I have is carbon and I have
three bulky group here so in this case a
nucleophile will not even do a lot the
bulky there is a bulky group on this
carbon the nucleophile won't be able to
attack right so it is good that the
carbon is one degree or at the max to
the right so bulky group is not
advisable
so that's why if you see the primary
halides are more reactive because in
driving halide is no bulky group ii
really did somebody group tertiary mobic
equal H of primary halides are
prone to sn2 reaction so the reactivity
of halides as I told our IBR CLF here
also better the living-room better it is
here also in both the reactions are
cases common actually so RI is the best
living room so better the living room
that's why it is easy for this halogen
to go out right so you have RI here can
easily be kicked out even the straw is a
neat nucleophile so the better the
living group the better it is so it is
common for both so you can ignore this
when you want to compare sn1 and sn2
reaction but this plays a critical role
right the reactivity or better leaving
group now let's understand the factors
affecting sn1 and sn2 its compare these
two reactions so observation is in
essence one we have seen the nucleophile
strength is not important because
nucleophile doesn't play any rule but in
sn2 the nucleophile strength plays a
critical role both sn1 and sn2 requires
a good living room that is something we
have seen in sn1 it is okay to have a
steric hindrance because it is the
halogen that decides it has to leave or
not right the nucleophile just comes and
places take that place right there is no
attack as such so the steric hindrance
doesn't make a difference it is good to
have a steric hindrance actually by with
the steric hindrance the kabocha time
formed is really more stable but in sn2
there is a steric hindrance it is very
difficult to have us into reaction
because it happens from the backside it
has to be space for attack protic
solvent if they told favours sn1
reaction why protic solvent encourages X
here right leave leave this compound and
form HX see there is a protic solvent X
H+ it encourages X to leap so protic
solvent favours sn1 reaction but a
protic solvent
favours sn2 reaction right and since sn2
reaction proceeds from the backside is a
told it is happening from the back side
from the back side so if there is a
studio center present we get inversion
the product is inversion so we will get
the make
Sheriff but for sn1 reaction we'll get
the mixture retention and inversion we
talk about these things also later let's
understand the concept see if it is sn2
reaction what is happening is I have let
suppose X so let suppose H h h and
relate suppose this is a this is B this
is C small small small and I have X I
have attacked from here of some
nucleophile so what I get here is if you
see the intermediate will be C V and a
all one plane then I have a nucleophile
and then I have X and further the X will
go up so I'll get something like this
nucleophile and then I'll get see a so
we see this inversion now earlier it's
or it was a BNC you see the inversion
happened right so it was a B and C in
this direction it becames a BNC research
so the inversion happened nucleophile
attack and enjoy this a this is B and
since you so since this attacked this
became a planar one for a moment moment
and then since the nucleophile attack
from this side this became inversion
because if you see the thing it changed
was ABC in this session becomes CBA will
will learn more about stereochemistry
the next few slides and you'll
understand this better actually so there
is an inversion of controllers
understand in case of as in to reaction
but in case of sn1 reaction if you see
the same thing let's suppose it goes for
sn1 reaction so the intermediate form
ABC and then it will be all plane
actually be on one plane C correct
well since the carbon is already there
let me put it be correct it will be a
kabocha time you see now the nucleophile
can attack from this side or from this
side both side so in this case you will
get the mixture of retention and
in version right because I am not able
to show you in this picture actually
this is except us carbon and this V T
this if it lacks from this side it will
form something like this let's suppose
there is a nucleophile n so it will form
C a B D and n correct and if it attacks
from this side it will form an e BN and
both are actually if you see different
Natalie both are optical isomers right
steel you Mars actually called you have
learned this in Graf 11 so in that case
we get both 50/50 so we get a mixture of
retention and inversion this is called
inversion because attacks from backside
and this is called retention because the
attack is from the front side but in
case of sn2 reaction since the attack is
only from backside we all only get
inversion understood say in case of sn1
the attack is from both side because one
the carbo cation is formed that back can
become any side right so it gives
inversion retention both but it's a
percent to the attack is overly from
backsides you always get inversion thank
you visit exam viacom to watch free
education videos try free online tests
get the best quality study materials
study from the best tutors and mentors
and much more
thanks and serene
in hilarious part 19 is brought to you
by exam flare calm no more fear from
exam let's talk about sn2 reaction let's
see the concept of us into reaction
there is a leaving group I mean there's
a compound here the leaving group air
and there is a very strong nucleophile
here this is a very strong nucleophile
this nucleophile can influence this atom
to move right in this nucleophile you
see can influence this atom to move and
this atom will have to move so in this
case the influence of this atom matters
also if you see there is no security
guards here right so no security guard
so had there been security guard this
lady would happen could not happen in to
influence this atom to go right there is
no security guard there is a strong
nucleophile this lady was strong these
things favors sn2 reaction so I have
someone who is very strong it comes it
influence kicks the person outs that is
sn2 reaction why it is sn2 reaction
because this is my mom
so the radiator manufacturers region
both to write both the strength of these
two besides what is the rate correct the
rate depends also on the reactant and
the nuclear so if you see this is a
typical example of sn2 reaction so this
was a reactant and this is my
nucleophile nucleophile is strong it
came and attack this guy from this side
see we see there was no security guard
no security hindrance now since this is
attacked this is the weak guy this is a
weak guy it left see the reaction is one
step back is all things happen one step
but the rate of the reaction depends on
two people right so it is sn2 reaction
these are the concept let's see the
reaction actually right
so in this case a lone pair of
nucleophile attacks the carbon
electrophilic carbon from the backside
please note backside is critical here
always the attack is from the backside
right and this expel another group this
is a leaving group so this nucleophile
attack this carbon this is a carbon from
the backside and like spin the living
room the blue one is the living room
right and this is one step this is one
set and thus since that is from the
backside it causes inversion will talk
about inversion in the next few slides
because see if you see is OS - hairs and
this hair if you see only one if I group
and two hydrogen so the space is there
for this - to attack right to security
goddess last only one security guard
actually so it can attack now there's a
transition stage it happens right and
then this voice - is linked and BR -
quito this is one step all one step but
sn2 why sin do because the slowest step
is my slowest step it is my slowest step
it involves two thing right this
involved two species one is the reactant
and one is a reagent so it is called sn2
it is by molecular nucleophilic
substitution reaction correct and
experimental it has been seen that the
rate of reaction depends both on the
reactant product so what they have done
is they have increase the reactants and
they have seen the rate of reaction
increase their increase the product
sorry they have increased the
nucleophile they have seen the rate of
reaction trees they have increase both
and they have seen the rate of in
reaction increases or means the rate of
reaction depends both on my reactants
and the nucleophile correct it is
attacked from back so there is something
called inversion because it's a diving
attack your back and we'll discuss more
about inversion in the next few slides
let's understand more about this
reaction
a protic solvent favors this why because
hey if this is a protic solvent coating
sulfonyl dawat if there is a halogen X
it is a halogen X let's suppose can
write this since this is a protic
solvent floating selim will try to
attract this halogen and will try to say
this halogen to leave on its own and
then it will become sn1 reaction because
if this halogen leaves on its own and
then some other Nick LaFollette is
attacking this becomes n1 reaction but
we don't want that we want someone to
attack from back for sn2 reactions so in
this case if it is a protic solvent it
is better so in that case there is no
what you call interface or there is no
disturbance or for these halogens there
is no extra reason or extra affinity of
these halogen to leave this particular
react
correct in this case there is no
intermediate form in sn1 you Eocene the
Cabo Verde Islands form in this case the
low intermediate form is all one step
process all one step process right and
in this case both subtract and attacking
legend they decide the rate of reaction
that's why it's called sn2 because there
are two species that decides the rate of
the reaction in this case a strong
nucleophile is too dry because i'm
saying to the nucleophile is attacking
right so that means the nucleophile
should be strong enough to attack to
kick this leaving rubout so if the
nucleophile is strong it is
added advantage inversion of control
takes place as I told explain what is
inversion of control in the next few
slides presence of bulky group near the
carbon atom has inhibiting effect for
example I have is carbon and I have
three bulky group here so in this case a
nucleophile will not even do a lot the
bulky there is a bulky group on this
carbon the nucleophile won't be able to
attack right so it is good that the
carbon is one degree or at the max to
the right so bulky group is not
advisable
so that's why if you see the primary
halides are more reactive because in
driving halide is no bulky group ii
really did somebody group tertiary mobic
equal H of primary halides are
prone to sn2 reaction so the reactivity
of halides as I told our IBR CLF here
also better the living-room better it is
here also in both the reactions are
cases common actually so RI is the best
living room so better the living room
that's why it is easy for this halogen
to go out right so you have RI here can
easily be kicked out even the straw is a
neat nucleophile so the better the
living group the better it is so it is
common for both so you can ignore this
when you want to compare sn1 and sn2
reaction but this plays a critical role
right the reactivity or better leaving
group now let's understand the factors
affecting sn1 and sn2 its compare these
two reactions so observation is in
essence one we have seen the nucleophile
strength is not important because
nucleophile doesn't play any rule but in
sn2 the nucleophile strength plays a
critical role both sn1 and sn2 requires
a good living room that is something we
have seen in sn1 it is okay to have a
steric hindrance because it is the
halogen that decides it has to leave or
not right the nucleophile just comes and
places take that place right there is no
attack as such so the steric hindrance
doesn't make a difference it is good to
have a steric hindrance actually by with
the steric hindrance the kabocha time
formed is really more stable but in sn2
there is a steric hindrance it is very
difficult to have us into reaction
because it happens from the backside it
has to be space for attack protic
solvent if they told favours sn1
reaction why protic solvent encourages X
here right leave leave this compound and
form HX see there is a protic solvent X
H+ it encourages X to leap so protic
solvent favours sn1 reaction but a
protic solvent
favours sn2 reaction right and since sn2
reaction proceeds from the backside is a
told it is happening from the back side
from the back side so if there is a
studio center present we get inversion
the product is inversion so we will get
the make
Sheriff but for sn1 reaction we'll get
the mixture retention and inversion we
talk about these things also later let's
understand the concept see if it is sn2
reaction what is happening is I have let
suppose X so let suppose H h h and
relate suppose this is a this is B this
is C small small small and I have X I
have attacked from here of some
nucleophile so what I get here is if you
see the intermediate will be C V and a
all one plane then I have a nucleophile
and then I have X and further the X will
go up so I'll get something like this
nucleophile and then I'll get see a so
we see this inversion now earlier it's
or it was a BNC you see the inversion
happened right so it was a B and C in
this direction it becames a BNC research
so the inversion happened nucleophile
attack and enjoy this a this is B and
since you so since this attacked this
became a planar one for a moment moment
and then since the nucleophile attack
from this side this became inversion
because if you see the thing it changed
was ABC in this session becomes CBA will
will learn more about stereochemistry
the next few slides and you'll
understand this better actually so there
is an inversion of controllers
understand in case of as in to reaction
but in case of sn1 reaction if you see
the same thing let's suppose it goes for
sn1 reaction so the intermediate form
ABC and then it will be all plane
actually be on one plane C correct
well since the carbon is already there
let me put it be correct it will be a
kabocha time you see now the nucleophile
can attack from this side or from this
side both side so in this case you will
get the mixture of retention and
in version right because I am not able
to show you in this picture actually
this is except us carbon and this V T
this if it lacks from this side it will
form something like this let's suppose
there is a nucleophile n so it will form
C a B D and n correct and if it attacks
from this side it will form an e BN and
both are actually if you see different
Natalie both are optical isomers right
steel you Mars actually called you have
learned this in Graf 11 so in that case
we get both 50/50 so we get a mixture of
retention and inversion this is called
inversion because attacks from backside
and this is called retention because the
attack is from the front side but in
case of sn2 reaction since the attack is
only from backside we all only get
inversion understood say in case of sn1
the attack is from both side because one
the carbo cation is formed that back can
become any side right so it gives
inversion retention both but it's a
percent to the attack is overly from
backsides you always get inversion thank
you visit exam viacom to watch free
education videos try free online tests
get the best quality study materials
study from the best tutors and mentors
and much more
thanks and serene
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Apr 20, 2026 Last updated
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