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Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
I
Aromatic Compound
Organic chemistry has two main divisions. One division
deals with aliphatic (fatty) compounds, the first compounds you
encountered in Organic Chemistry I. The second division includes the
aromatic (fragrant) compounds, of which benzene is a typical example.
Chemists proposed many structures for benzene. However, the facts
didnโ€™t support any of the possibilities until Kekulรฉ proposed a ring
structure in 1865. Some of the proposed structures, including Kekulรฉโ€™s
one.
I. Nomenclature of Aromatic Cpd.s
1.General rules for naming;
1. Benzene derivatives are named by pre๏ฌxing the name of the
substituent group to the word benzene, e.g. chlorobenzene and
nitrobenzene.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
II
2. Disubstituted benzene with identical groups; the relative positions
have to be identi๏ฌed.
(1,2 = o; ortho โ€“ 1,3 = m; meta โ€“ 1,4 = para)
o-dimethylbenzene m-dibromobenzene
3.Disubstituted benzene with different groups;
According to the priority, parent name is detected.
Aniline. Phenol, Benzaldehyde and benzoic acid will be considered the
parent name.
p-Chlorostyrene p-methylphenol
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
III
4. When more than two substituent,, use the no. to express the positions.
If the groups are different, then the last-named group is understood to
be in position 1.
5.Long carbon chain has the priority,,,
Unsaturated chain has the priority,,,
(that rule can be neglected)
(2E-2-phenyl-2-butane phenyldecan
*benzene as a substituent;
-Aryl group; Ar-:
Aromatic hydrocarbons are sometimes called arenes.
Ar- is the aromatic group that remains after the removal of a hydrogen
atom from an aromatic ring.
examples of aryl groups:
examples of generic aryl groups:
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
IV
-phenyl group; Ph (or โˆ… ):
The phenyl group is used in the name just like the name of an alkyl
group.
examples of phenyl groups:
-benzyl group;
The seven-carbon unit consisting of a benzene ring and a methylene
(-๐‘ช๐’‰ ๐Ÿ-) group.
examples of benzyl group:
*practical quiz;
Name the following structures:
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
V
II. Study of Benzene ring
Rx. Of benzene ring!
If benzene contains three double bonds, why, his critics asked, doesnโ€™t
it show the reactions typical of alkenes?
It is easier to break ๐… bond than breaking ๐ˆ bond but it broke ๐ˆ as the
๐… bond gains stability from benzene structure system.
1.Measurement of the benzene ring stability
Using halogenation!!! As a process used to measure the stability of
benzene in a comparison with series of related compounds that have
๐…bond giving a difference in the energy values,,, stabilization energy..
The presence of resonance in the benzene makes it harder to break the
3 double bonds and to break it, it costs high energy.
***Note;
- Def. of,,
*Stabilization energy ;
the difference between the supposed released energy and the actually
released energy.
*Entropy ; freedom of electrons.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
VI
So energetically , benzene cannot behave as an alkene,,
2. Theories of benzene stability explanation
I. Resonance Theory
*(overview)
Resonance;
the extra stabilization provided by delocalization, compared with a
localized structure.
delocalization is gained from migration of e' of ๐… bonds as the weak
overlapping or unshared e'.
Contributing Structures
๐‘บ๐‘ท ๐Ÿ
hybridization
Give reason;
Resonance increase the stability.
Resonance cause dispersion of charges (-ve charges of e')
and it's spread over the atoms so, it decreases the entropy and increase
the stability.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
VII
1. The ๐… bond = ๐† orbital + ๐† orbital ,,, that remain after hybridization
( ๐‘บ๐‘ท ๐Ÿ
).
2. Resonance forms are imaginary, not real.
3. Resonance structures differ only in the positions of their electrons.
4. Different resonance forms do not have to be equivalent.
5. The more resonance structures there are, the more stable the
molecule is.
6. Orbital;The SPACE that provide an opportunity for e' migration.
*Kekule structure & its explanation for the benzene stability;
As the approch of Kekule's structure and
the above theory, it would be a conclusion
that the stability of the benzene structure is
a result of the resonance som it's the aromaticity!
"What we need to catch a reason for it".
Unfortionately, this words fail to explain the followingโ€ฆ
Cyclobutadiene Cyclooctatraiene
Both show resonance but they are NOT show the aromaticity at all
conditions. Cyclobutadiene and cyclooctatetraene have alternating
single and double bonds similar to those of benzene. These compounds
were mistakenly expected to be aromatic.
*Note: all annulenes show resonance but not aromatic.
- Annulene: these cyclic hydrocarbons with alternating single and
double bonds.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
VIII
II. Organic math โ€” Hรผckelโ€™s Rule of aromaticity
Following are the requirements for a species to be aromatic:
I. Aromatic compounds
1. The compound must contain a ring system ,, (cyclic).
2. The system must be planar (or nearly planar), p orbitals are parallel.
3. The system is unsaturated conjugated.
"each atom in the ring must have an unhybridized p-orbital
perpendicular to the plane of the ring,,," (all p orbitals are parallel).
This means that an sp3 atom cannot be part of an aromatic system.
4. The ring system must have a Hรผckel number of ฯ€-electrons
*No of ๐… electrons = 4n + 2 ,,, " N is a positive integer".
e.g. Benzene
no. of e' = 6 ,,, SO, 4n + 2 = 6
4n = 4
โˆด Benzene is AROMATIC n = 1 "+ve integer"
II. Anti-aromatic compounds
1. The compound must contain a ring system ,, (cyclic).
2. The system must be planar.
3. The system is conjugated.
4. Do NOT obey Hรผckel number of ฯ€-electrons.
*No. of ๐… electrons = 4n + 2 ,,, " n is not a positive integer".
but obey โ€ฆ
or, ๐… electrons = 4n " n is a positive integer "
e.g. cyclopentadienyl cation
no. of e' = 4 ,,, SO, 4n = 4
n = 1 "+ve integer"
โˆด cyclopentadienyl cation is ANTI-AROMATIC
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
IX
III. Non-Aromatic compounds
*the compound has not one point of the mentioned above*
- Non cyclic conjugated.
Or,
- has non planer configuration.
Or,
- no unhybridized p- orbital for an atom with non-conjugated system.
III. Molecular Orbital Theory & Frost Circle
*MOT (overview)
The key difference is that in molecular orbitals, the electrons are
allowed to interact with more than one atomic nucleus at a time. Just as
with atomic orbitals.
MOT in points;
1. MO = AO + AO So, no. of molecular orbitals = no. of atomic orbitals.
2. There are 3 types (bonding, anti-bonding, non- bonding) that differ
in:
*type of overlap.
*energy.
3. M.O. is formed according to respectable view of:
-Hund's rule.
-Aufbau principle. Just a good knowledge of them is fair.
-Pauli exclusion principle.
*Hund's rule; orbital in a subshell is singly occupied with one electron
before any one orbital is doubly occupied, and all electrons in singly
occupied orbitals have the same spin.
(No pairing even it's being a single in the required position)
*Aufbau principle; electrons orbiting one or more atoms fill the lowest
available energy levels before filling higher levels.
*Pauli exclusion principle; No two electrons in an atom
can have identical quantum numbers.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
X
principles in developing a molecular orbital representation for
benzene;
1. There are six atomic p orbitals that overlap to form the benzene ๐…
system. Therefore, there must be six molecular orbitals.
2. The lowest-energy molecular orbital is entirely bonding, with
constructive overlap between all pairs of adjacent p orbitals. There are
no vertical nodes in this lowest-lying MO.
3. The number of nodes increases as the MOs increase in energy.
4. The MOs should be evenly divided between bonding and antibonding
MOs, with the possibility of nonbonding MOs in some cases.
5. We expect that a stable system will have filled bonding MOs and
empty antibonding MOs.
Are you confused ?! let me simplify that by a simple example at first.
*Molecular Orbitals for the ๐‘ฏ ๐Ÿ Molecule
that diagram deliver the meaning of the constructive and deconstructive
wave which are formed according to the type of interaction,
*head โ€“ head interaction โ€ฆ
*side-by-side interaction โ€ฆ
If you still can't collect the fragments of that point, do not worry at all.
but you must be able to apply the following by yourself, "your hand
writing I mean"โ€ฆ
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XI
Molecular Orbital Energy-Level Diagram for ๐‘ฏ ๐Ÿ;
Now, let yourself to draw the same diagram for benzene;
Energy diagram of the molecular orbitals of benzene.
Benzeneโ€™s six electrons fill the three bonding orbitals,
leaving the antibonding orbitals vacant.
but how we can imagine that more and more
simple..
"picture is better than thousands of books"
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XII
The first MO is all-bonding and
is particularly stable. The second and third (degenerate) MOs
are still strongly bonding, and all three of these bonding
MOs delocalize the electrons over several nuclei. This configuration,
with all the bonding MOs filled (a โ€œclosed bonding shellโ€), is
energetically very favorable.
*The most important point is the conclusion that state "if the pairing
occurred in the bonding M.O. so, it's AROMATIC but the must be
completely filled with e' as bonding M.O. are at lower level; therefore,
lower energy and higher stability that means the high stable compounds
are aromatic compounds.
-Using the same concept, we can study if cyclobutadiene is aromatic or
notโ€ฆ
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XIII
*Frost Circle;
A simple method used to estimate the relative ฯ€ orbital energies of both
planar and cyclic compounds with an uninterrupted ฯ€ electron system.
Steps to draw Frost circle;
1. Draw a circle.
2. Draw the compound into the circle by touching each boundary point
by the circle circumference and starting from below.
3. Put small line at every point of intersection;
-Upper half: Antibonding M.O.
-Diameter: Nonbonding M.O.
-Lower half: Bonding M.O.
๐† ๐Ÿ ๐† ๐Ÿ ๐† ๐Ÿ‘ ๐† ๐Ÿ’ ๐† ๐Ÿ“ ๐† ๐Ÿ”
*No e' in non-bonding M.O. so, it is AROMATIC.
e.g: cycloheptatrienyl anion
*The end*
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XIV
*Exercise Sheet*
1. Draw the structure of each compound:
(a) o-nitroanisole
(b) 2,4-dimethoxyphenol
(c) p-aminobenzoic acid
(d) 4-nitroaniline
(e) m-chlorotoluene
(f) p-divinylbenzene
(g) p-bromostyrene
(h) 3,5-dimethoxybenzaldehyde
(i) tropylium chloride
(j) sodium cyclopentadienide
(k) 2-phenylpropan-1-ol
(l) benzyl methyl ether
(m) p-toluenesulfonic acid
(n) o-xylene
(o) 3-benzylpyridine
2. Name the following compounds:
3. Give Reason;
Cyclopentadiene is acidic.
(Final 2009, 2013, 2014 midterm, 2015)
4.How can you predict the aromatic, antiaromatic cycles of the
following;
*The answer must be powered by Hรผckelโ€™s criteria, MOT & the aid of
Frost circle*
I. Cyclopropenyl cation.
II. Cylopentadiene anion.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XV
III. The forced planner form of (8) annulene.
(Final 2005, 2013, 2014)
5.Write the resonance structure for the cyclopentadienyl anion.
6.Give Reason;
Cyclobytadiene is antiaromatic.
(Midterm 2010, 2013, 2014)
7.Discuss the aromaticity of Cyclopentadiene.
8.Study the aromaticity of Cyclooctatraien, Cyclopropene,
Cyclopentadiene, Cycloheptatriene.
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XVI
Helpful Sheet
Classes of Aromatic Compounds
Alkylbenzene & Alkenylbenzene;
Toluene o-xylene m-xylene p-xylene
styrene allyl benzene 2-phenyl-2-butene
vinyl benzene 3-phenylpropene
phenyl ethylene
** The simplest alkenyl benzenes are called styrenes.
Aryl Halides;
flurobenzene chlorobenzene bromobenzene Iodobenzene
Aralkyl Halides;
benzyl Chloride 1-phenyl Chloride 2-phenylethyl chloride
1-chloroethylbenzene
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XVII
Nitro-compounds;
Nitrobenzene T.N.B T.N.T
Aniline p-Toluidine m-Toluidine
Aromatic Diazonium salts;
Benzene Diazonium Chloride
Phenols;
Phenol O-cresol m-cresol p-cresol
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XVIII
catechol Resorcinol Quinol
Aromatic Alcohols;
Benzyl alcohol 2-phenylethanol 1-phenylethanol
Aromatic ethers;
Methoxybenzene Ethoxybenzene o-Anisidine o-Phenitidine
Aromatic Aldehyde & Ketones;
Benzaldehyde o-Anisaldehyde Acetylbenzene Buterylbenzene
(Acetaphenone) (Buterophenone)
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XIX
Aromatic Acids;
Benzoic acid Salicylic acid Phthalic acid
If you can't explain it simply, you don't
understand it well enough.
- Albert Einstein
Dr.M_T The 3rd Vision Academy 01156281369
ASU 1 ๐‘ ๐‘ก
year 2016
XX
*Table of Functional Group Priorities For Nomenclature;

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Aromatic Comp. Lec.1

  • 1. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 I Aromatic Compound Organic chemistry has two main divisions. One division deals with aliphatic (fatty) compounds, the first compounds you encountered in Organic Chemistry I. The second division includes the aromatic (fragrant) compounds, of which benzene is a typical example. Chemists proposed many structures for benzene. However, the facts didnโ€™t support any of the possibilities until Kekulรฉ proposed a ring structure in 1865. Some of the proposed structures, including Kekulรฉโ€™s one. I. Nomenclature of Aromatic Cpd.s 1.General rules for naming; 1. Benzene derivatives are named by pre๏ฌxing the name of the substituent group to the word benzene, e.g. chlorobenzene and nitrobenzene.
  • 2. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 II 2. Disubstituted benzene with identical groups; the relative positions have to be identi๏ฌed. (1,2 = o; ortho โ€“ 1,3 = m; meta โ€“ 1,4 = para) o-dimethylbenzene m-dibromobenzene 3.Disubstituted benzene with different groups; According to the priority, parent name is detected. Aniline. Phenol, Benzaldehyde and benzoic acid will be considered the parent name. p-Chlorostyrene p-methylphenol
  • 3. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 III 4. When more than two substituent,, use the no. to express the positions. If the groups are different, then the last-named group is understood to be in position 1. 5.Long carbon chain has the priority,,, Unsaturated chain has the priority,,, (that rule can be neglected) (2E-2-phenyl-2-butane phenyldecan *benzene as a substituent; -Aryl group; Ar-: Aromatic hydrocarbons are sometimes called arenes. Ar- is the aromatic group that remains after the removal of a hydrogen atom from an aromatic ring. examples of aryl groups: examples of generic aryl groups:
  • 4. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 IV -phenyl group; Ph (or โˆ… ): The phenyl group is used in the name just like the name of an alkyl group. examples of phenyl groups: -benzyl group; The seven-carbon unit consisting of a benzene ring and a methylene (-๐‘ช๐’‰ ๐Ÿ-) group. examples of benzyl group: *practical quiz; Name the following structures:
  • 5. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 V II. Study of Benzene ring Rx. Of benzene ring! If benzene contains three double bonds, why, his critics asked, doesnโ€™t it show the reactions typical of alkenes? It is easier to break ๐… bond than breaking ๐ˆ bond but it broke ๐ˆ as the ๐… bond gains stability from benzene structure system. 1.Measurement of the benzene ring stability Using halogenation!!! As a process used to measure the stability of benzene in a comparison with series of related compounds that have ๐…bond giving a difference in the energy values,,, stabilization energy.. The presence of resonance in the benzene makes it harder to break the 3 double bonds and to break it, it costs high energy. ***Note; - Def. of,, *Stabilization energy ; the difference between the supposed released energy and the actually released energy. *Entropy ; freedom of electrons.
  • 6. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 VI So energetically , benzene cannot behave as an alkene,, 2. Theories of benzene stability explanation I. Resonance Theory *(overview) Resonance; the extra stabilization provided by delocalization, compared with a localized structure. delocalization is gained from migration of e' of ๐… bonds as the weak overlapping or unshared e'. Contributing Structures ๐‘บ๐‘ท ๐Ÿ hybridization Give reason; Resonance increase the stability. Resonance cause dispersion of charges (-ve charges of e') and it's spread over the atoms so, it decreases the entropy and increase the stability.
  • 7. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 VII 1. The ๐… bond = ๐† orbital + ๐† orbital ,,, that remain after hybridization ( ๐‘บ๐‘ท ๐Ÿ ). 2. Resonance forms are imaginary, not real. 3. Resonance structures differ only in the positions of their electrons. 4. Different resonance forms do not have to be equivalent. 5. The more resonance structures there are, the more stable the molecule is. 6. Orbital;The SPACE that provide an opportunity for e' migration. *Kekule structure & its explanation for the benzene stability; As the approch of Kekule's structure and the above theory, it would be a conclusion that the stability of the benzene structure is a result of the resonance som it's the aromaticity! "What we need to catch a reason for it". Unfortionately, this words fail to explain the followingโ€ฆ Cyclobutadiene Cyclooctatraiene Both show resonance but they are NOT show the aromaticity at all conditions. Cyclobutadiene and cyclooctatetraene have alternating single and double bonds similar to those of benzene. These compounds were mistakenly expected to be aromatic. *Note: all annulenes show resonance but not aromatic. - Annulene: these cyclic hydrocarbons with alternating single and double bonds.
  • 8. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 VIII II. Organic math โ€” Hรผckelโ€™s Rule of aromaticity Following are the requirements for a species to be aromatic: I. Aromatic compounds 1. The compound must contain a ring system ,, (cyclic). 2. The system must be planar (or nearly planar), p orbitals are parallel. 3. The system is unsaturated conjugated. "each atom in the ring must have an unhybridized p-orbital perpendicular to the plane of the ring,,," (all p orbitals are parallel). This means that an sp3 atom cannot be part of an aromatic system. 4. The ring system must have a Hรผckel number of ฯ€-electrons *No of ๐… electrons = 4n + 2 ,,, " N is a positive integer". e.g. Benzene no. of e' = 6 ,,, SO, 4n + 2 = 6 4n = 4 โˆด Benzene is AROMATIC n = 1 "+ve integer" II. Anti-aromatic compounds 1. The compound must contain a ring system ,, (cyclic). 2. The system must be planar. 3. The system is conjugated. 4. Do NOT obey Hรผckel number of ฯ€-electrons. *No. of ๐… electrons = 4n + 2 ,,, " n is not a positive integer". but obey โ€ฆ or, ๐… electrons = 4n " n is a positive integer " e.g. cyclopentadienyl cation no. of e' = 4 ,,, SO, 4n = 4 n = 1 "+ve integer" โˆด cyclopentadienyl cation is ANTI-AROMATIC
  • 9. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 IX III. Non-Aromatic compounds *the compound has not one point of the mentioned above* - Non cyclic conjugated. Or, - has non planer configuration. Or, - no unhybridized p- orbital for an atom with non-conjugated system. III. Molecular Orbital Theory & Frost Circle *MOT (overview) The key difference is that in molecular orbitals, the electrons are allowed to interact with more than one atomic nucleus at a time. Just as with atomic orbitals. MOT in points; 1. MO = AO + AO So, no. of molecular orbitals = no. of atomic orbitals. 2. There are 3 types (bonding, anti-bonding, non- bonding) that differ in: *type of overlap. *energy. 3. M.O. is formed according to respectable view of: -Hund's rule. -Aufbau principle. Just a good knowledge of them is fair. -Pauli exclusion principle. *Hund's rule; orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. (No pairing even it's being a single in the required position) *Aufbau principle; electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels. *Pauli exclusion principle; No two electrons in an atom can have identical quantum numbers.
  • 10. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 X principles in developing a molecular orbital representation for benzene; 1. There are six atomic p orbitals that overlap to form the benzene ๐… system. Therefore, there must be six molecular orbitals. 2. The lowest-energy molecular orbital is entirely bonding, with constructive overlap between all pairs of adjacent p orbitals. There are no vertical nodes in this lowest-lying MO. 3. The number of nodes increases as the MOs increase in energy. 4. The MOs should be evenly divided between bonding and antibonding MOs, with the possibility of nonbonding MOs in some cases. 5. We expect that a stable system will have filled bonding MOs and empty antibonding MOs. Are you confused ?! let me simplify that by a simple example at first. *Molecular Orbitals for the ๐‘ฏ ๐Ÿ Molecule that diagram deliver the meaning of the constructive and deconstructive wave which are formed according to the type of interaction, *head โ€“ head interaction โ€ฆ *side-by-side interaction โ€ฆ If you still can't collect the fragments of that point, do not worry at all. but you must be able to apply the following by yourself, "your hand writing I mean"โ€ฆ
  • 11. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XI Molecular Orbital Energy-Level Diagram for ๐‘ฏ ๐Ÿ; Now, let yourself to draw the same diagram for benzene; Energy diagram of the molecular orbitals of benzene. Benzeneโ€™s six electrons fill the three bonding orbitals, leaving the antibonding orbitals vacant. but how we can imagine that more and more simple.. "picture is better than thousands of books"
  • 12. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XII The first MO is all-bonding and is particularly stable. The second and third (degenerate) MOs are still strongly bonding, and all three of these bonding MOs delocalize the electrons over several nuclei. This configuration, with all the bonding MOs filled (a โ€œclosed bonding shellโ€), is energetically very favorable. *The most important point is the conclusion that state "if the pairing occurred in the bonding M.O. so, it's AROMATIC but the must be completely filled with e' as bonding M.O. are at lower level; therefore, lower energy and higher stability that means the high stable compounds are aromatic compounds. -Using the same concept, we can study if cyclobutadiene is aromatic or notโ€ฆ
  • 13. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XIII *Frost Circle; A simple method used to estimate the relative ฯ€ orbital energies of both planar and cyclic compounds with an uninterrupted ฯ€ electron system. Steps to draw Frost circle; 1. Draw a circle. 2. Draw the compound into the circle by touching each boundary point by the circle circumference and starting from below. 3. Put small line at every point of intersection; -Upper half: Antibonding M.O. -Diameter: Nonbonding M.O. -Lower half: Bonding M.O. ๐† ๐Ÿ ๐† ๐Ÿ ๐† ๐Ÿ‘ ๐† ๐Ÿ’ ๐† ๐Ÿ“ ๐† ๐Ÿ” *No e' in non-bonding M.O. so, it is AROMATIC. e.g: cycloheptatrienyl anion *The end*
  • 14. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XIV *Exercise Sheet* 1. Draw the structure of each compound: (a) o-nitroanisole (b) 2,4-dimethoxyphenol (c) p-aminobenzoic acid (d) 4-nitroaniline (e) m-chlorotoluene (f) p-divinylbenzene (g) p-bromostyrene (h) 3,5-dimethoxybenzaldehyde (i) tropylium chloride (j) sodium cyclopentadienide (k) 2-phenylpropan-1-ol (l) benzyl methyl ether (m) p-toluenesulfonic acid (n) o-xylene (o) 3-benzylpyridine 2. Name the following compounds: 3. Give Reason; Cyclopentadiene is acidic. (Final 2009, 2013, 2014 midterm, 2015) 4.How can you predict the aromatic, antiaromatic cycles of the following; *The answer must be powered by Hรผckelโ€™s criteria, MOT & the aid of Frost circle* I. Cyclopropenyl cation. II. Cylopentadiene anion.
  • 15. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XV III. The forced planner form of (8) annulene. (Final 2005, 2013, 2014) 5.Write the resonance structure for the cyclopentadienyl anion. 6.Give Reason; Cyclobytadiene is antiaromatic. (Midterm 2010, 2013, 2014) 7.Discuss the aromaticity of Cyclopentadiene. 8.Study the aromaticity of Cyclooctatraien, Cyclopropene, Cyclopentadiene, Cycloheptatriene.
  • 16. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XVI Helpful Sheet Classes of Aromatic Compounds Alkylbenzene & Alkenylbenzene; Toluene o-xylene m-xylene p-xylene styrene allyl benzene 2-phenyl-2-butene vinyl benzene 3-phenylpropene phenyl ethylene ** The simplest alkenyl benzenes are called styrenes. Aryl Halides; flurobenzene chlorobenzene bromobenzene Iodobenzene Aralkyl Halides; benzyl Chloride 1-phenyl Chloride 2-phenylethyl chloride 1-chloroethylbenzene
  • 17. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XVII Nitro-compounds; Nitrobenzene T.N.B T.N.T Aniline p-Toluidine m-Toluidine Aromatic Diazonium salts; Benzene Diazonium Chloride Phenols; Phenol O-cresol m-cresol p-cresol
  • 18. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XVIII catechol Resorcinol Quinol Aromatic Alcohols; Benzyl alcohol 2-phenylethanol 1-phenylethanol Aromatic ethers; Methoxybenzene Ethoxybenzene o-Anisidine o-Phenitidine Aromatic Aldehyde & Ketones; Benzaldehyde o-Anisaldehyde Acetylbenzene Buterylbenzene (Acetaphenone) (Buterophenone)
  • 19. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XIX Aromatic Acids; Benzoic acid Salicylic acid Phthalic acid If you can't explain it simply, you don't understand it well enough. - Albert Einstein
  • 20. Dr.M_T The 3rd Vision Academy 01156281369 ASU 1 ๐‘ ๐‘ก year 2016 XX *Table of Functional Group Priorities For Nomenclature;