Download ORGANIC CHEMISTRY NOTES , 2s , 2px , 2py , 2pz , 2s , 2px , 2py

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and 2py change shape and form 3 sigma bonds
as shown in the diagram. Where as the 2pz
ORGANIC CHEMISTRY NOTES
orbital remains unchanged. These half-filled 2pz
orbitals overlap sideways and form a ring of
delocalized electrons above and below the
Interpret and Use the Nomenclature, General
hexagonal structure as shown.
Formula, Displayed Formula of the following
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Arenes
HalagenoArenes
Phenols
AcylChlorides
Amides and Amino Acids
ARENES
Arenes are derivatives of Benzene which are
Cyclic unsaturated hydrocarbons .
Physical Properties
Arenes have relatively high melting/boiling
points due to greater van der waals dispersion
forces due to delocalized electrons
Insoluble in water
IUPAC Priority Rules
Electronic configuration of Carbon in ground
2
2
1
1
0
2
1
1
1
1
state 1s , 2s , 2px , 2py , 2pz . Carbon
only has 2 half-filled outermost orbitals for
bonding. By promoting one electron from 2s
orbital to 2pz orbital and going into excited
state 1s , 2s , 2px , 2py , 2pz it can now
form 4 bonds which is more exothermic and
leads to more stability.
1- Carboxylic Acids and Derivatives (esters,
acylchlorides, amides)
2- Nitriles (prefix: cyano, suffix: nitrile)
3- Aldehyde(suffix: -al)
4- Ketone (suffix: -one)
5- Alcohols (prefix: hydroxyl, suffix:-ol)
6- Ammines (prefix:amino, suffix:amines)
7Naming Aromatic Hydrocarbons which are
derivatives of Alkenes
Multiple substituents should be named by
giving the smallest number to each substituent
in either direction of the ring
Carbon undergoes sp2 hybridization in benzene,
where 3 half-filled outermost orbitals 2s, 2px,
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Bromine and Chlorine are not electronegative
enough to attack benzene.
FeCl3 and FeBr3 form metal complexes with Cl2
and Br2. The lone pair of Cl2/Br2 is then used for
dative bonding with Fe. This increases
electronegativity of Cl2/Br2.
Benzene group as a side chain is known as
Phenyl.
Halagen Substituents
Florine, Chlorine, Bromine, Iodine have exactly
the same priority as alkyl chains. Floro-, Chloro-,
Bromo-, Iodo- prefixes are used.
Alkyl chains and halogen substituents are
written in alphabetical order.
2-4-6 Directing Groups and 3-5 Directing Groups
FeBr3 and AlCl3 act as Lewis acids (electron pair
acceptor)
-CH3, -OH, -NH2 are 2-4-6 directing
Nucleophilic Substitution Reaction in Methyl
Benzene and Chlorine
They increase electron cloud density on the 2nd,
4th and 6th C atom
Boiling MethylBenzene or Benzene with Cl2 in
the absence of catalyst and presence of UV light
-NO2, -COOH are 3-5 directing
The N and C atom are attached to an
electronegative O atom which pull electrons
away from the benzene cloud.
Electrophilic Substitution Reaction of Benzene
and Methyl Benzene with Chlorine/Bromine
Benzene is highly attracted to electrophiles due
to delocalized electrons but the delocalized
electron cloud has extra stability and the
reaction is more difficult compared to alkenes.
Catalysts are therefore required for this
reaction.
Nitration of Benzene (electrophilic substitution)
To substitute NO2 in the Benzene ring, you
would need NO2+1 (nitronium ion).
HNO3 is mixed with H2SO4 to get this
electrophile.
HNO3 + 2 H2SO4 
NO2+1 +
HSO4-1
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benzene ring to provide extra strength to the
+ H3O+1
bond.
Nucleophilic substitution (like those in
halogenoalkanes) only occurs under very severe
condition.
Physical properties: They are liquids and
insoluble in water.
PHENOLS
Position of Substituent in the product
Nitro substituent is 3-5 directing
Methyl substituent is 2-4 directing
Phenols are way more acidic than alcohols, and
its delocalized ring is more reactive than
benzene.
The Lone pair on the oxygen
atom, starts to overlap with
the delocalized electron cloud
on the benzene. The makes
the oxygen-benzene bond
even stronger and more stable. Hence
nucleophilic substitution, similar to aliphatic
alcohols is not possible in Phenol
It also reduces the strength of the O-H bond
which make it easier for H+1 to ionize.
Oxidation of Arenes
ARYL HALIDES
Chloro benzene is highly unreactive. The extra
lone pairs on the Cl atom overlap with
the delocalized electrons in the
The phenoxide ion formed above, when phenol
loses an H+1 is very stable as the negative charge
on “O” gets delocalized over the entire benzene
ring. The extra stability of the phenoxide ion
shifts the equilibrium towards right and makes
phenol more acidic
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-OH group is 2-4-6 directing
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a) Reactions with Dilute Nitric Acid at
Phenols are stronger acids compared to
R.T.P gives 2-nitrophenol and 4aliphatic alcohols
nitrophenol
(Phenols>water>aliphatic alcohols)
Phenols Neutralize Strong Bases
Due to their weak acidity.
b) Reactions with Concentration Nitric
Acid leads to more than one
electrophilic substitutions due to
activated benzene ring
Addition of a strong acid to sodium phenoxide
recovers phenol
c) Aqueous Bromine gets decolorized at
room temperature when mixed with
aqueous Phenol. White precipitate of
2,4,6-tribromophenol is produced.
Reactions with Sodium
Phenol reacts vigorously with Sodium, greater
reactivity compared to reactions with Aliphatic
alcohols.
IodoForm Reaction and Identification of
CH3CHOH- Group or CH3CO- Group
Reagents: Iodine mixed in NaOH and gentle or
no heat
Electrophilic Substitution Reactions for Phenol
(Nitration and Bromination of Phenol)
Delocalized Electron cloud in Phenols is way
more active compared to benzene due to
increased electron charge density.
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A pale yellow precipitate of tri-iodo methane,
–COOH group would therefore make the acid
CHI3, is obtained which gives evidence of the
even less acidic, and would not favor
presence of CH3CHOH- group
dissociation.
In the above diagram, Notice the formation of
an Aldehyde in Step (2). The “H” present in (2)
can also be an Alkyl Chain. The same test would
also be useful in identifying CH3CO- group as
aldehydes/ketones are already being produced
as intermediates in the reaction with alcohols.
If an “H” atom in the alkyl chain is substituted
by an electronegative specie like “Cl” then a
negative inductive effect would take place
which would pull the electron density away
from the –COO-1 atoms and making the ion
more stable
ACYL CHLORIDES
Strength of Organic Acids
CH3ClCOOH ↔ CH3ClCOO-1 + H+1
(higher pKa value means lower
dissociation/weaker acid)
CH3COOH ↔ CH3COO-1 + H+1
pKa=2.86
Hence a stronger acid is formed when
compared its counterpart CH3COOH.
pKa = 3.75
CH3CH2COOH ↔ CH3CH2COO-1 + H+1 pKa=4.76
The strength of an acid depends on the stability
of the ethanoate ion R-COO-1.
When –COOH dissociates, the negative charge
on –COO-1 spreads over the two oxygen atoms.
More negative charge on these two oxygen
atoms makes this ion unstable and this favors
the reverse reaction making the acid less acidic.
Alky groups have a positive inductive effect and
increase the electron density on the two oxygen
atoms which increases the negative charge on
these atoms. Bigger alkyl chains attached to the
FORMATION OF ACYL CHLORIDES
Carboxylic acids undergo nucleophilic
substitution reactions to produce the
corresponding acyl chloride.
PCl3 and SOCl2 are heated with carboxylic acid:
3 RCOOH + PCl3  3 RCOCl + H3PO4
RCOOH + SOCl2  RCOCl + SO2 + HCl
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HYDROLYSIS OF ACYL CHLORIDES
Acyl chlorides are more susceptible to
nucleophilic attacks due to the presences of
partial positive C atom which is bonded to “O”
and “Cl” which are extremely electronegative.
This was not the case in –COOH, where the
attached OH group had an electron pushing
effect, unlike Cl.
React vigorously with water
Carbon in Acyl Chlorides is bonded to two
electronegative elements, which gives it a large
partial positive charge and susceptible to
nucleophilic attack.
Carbon in Alkyl Chlorides (or halagenoalkanes)
is also partial positive but the charge is not as
high compared to acyl chlorides.
Carbon in Aryl Chlorides is surrounded by
delocalized electrons which hide the partial
positive charge making it the least susceptible
to a nucleophilic attack
React vigorously with Alcohols to form Esters
Reaction mechanism given below(not required)
Reaction mechanism given below (not required)
Ease of Hydrolysis of Acyl Chlorides, Aryl
Chlorides, Alkyl Chlorides
Acyl Chloride > Alkyl Chloride > Aryl Chloride
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React Readily with Phenols on Warming
Basic Nature of Ammines
Phenyl ethanoate is formed in the above
reaction.
Phenol is dissolved in NaOH (aq) and warmed
with ethanoyl chloride.
Nitrogen has one lone pair which can accept a
proton and form a dative bond.
Reaction with Ammonia and Primary Ammines
Another example of a vigorous nucleophilic
substitution
Excess ammonia produced reacts with HCl,
which produces NH4Cl
Primary Ammines react in a similar manner;
The ability of the nitrogen atom to accept a
proton depends on the strength of the negative
charge on the lone pair
i)
ii)
NITROGEN
COMPOUNDS
Formation of Ethyl Ammine and Phenyl
Ammine through reduction
Where [H] is a reducing agent LiAlH4 (lithium
tetra hydrido borate).
or
Where nitrile is heated with H2 gas and a nickel
or palladium catalyst.
Primary ammines are most basic as
alkyl groups have an electron
pushing effect (positive inductive
effect) which increases the charge
on Nitrogen atom’s lone pair
Phenyl ammine is the least basic as
the lone pair gets delocalized over
the entire benzene ring and then
negative charge gets spread out
and less intense, which therefore
doesn’t accept H+1 that easily.
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First step: Dissolve Phenol in NaOH
Reaction of Phenyl Ammine with Br2(aq)
Ammine is 2,4,6 directing and increases the
negative charge on the benzene ring,
activating it and making it susceptible to
electrophilic attack
Then add the mixture to a diazonium salt,
reaction takes place < 10C. A bright yellow
precipitate is obtained in the following reaction.
(diazonium ion acts as an electrophile)
The “–N=N -“ group in the compound is known
as the Azo group.
This is one method of producing very intense
and stable dyes which do not fade easily.
Other examples of Azo Dyes:
Methyl Orange:
Bromine water gets decolorized and white ppt
of 2,4,6-tribromophenylammine is obtained
Phenylamine and Diazonium Salt
Ionic Eq:
Temperature has to be kept below 10 C.
Reagents: Phenyl amine and HCl, below 10 C are
mixed with NaNO3.
AMINO ACIDS as ZWITTER IONS
Formation of Azodyes
An Amino Acid:
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Proteins are one form of Polypeptides. The
presence of N-H in polypeptides causes
hydrogen bonds to be formed.
Hydrolysis of Proteins
A zwitter ion has no overall electrical charge but
contains separate parts which are positively and
negatively charged.
Adding an Alkali:
Proteins are heated with 6 mol/dm3 Hydrogen
for 24 hours at 1100C.
Adding an Acid:
Formation of Peptides from Amino Acids
Amides have this link (Peptide
Linkage)
Polypeptides will have multiple amino acids
joined together through condensation
polymerization