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Formation And Trapping Of Benzyne Biology Essay

Back ground: Benzyne (didehydrobenzene) is an example of an aryne (-yne = triple bond) ,derivative of benzene produced by abstraction of two hydrogen atoms, especially one produced by abstraction from neighbouring atoms to produce a formal triple bond. Benzyne is a reactive intermediate, which tends to undergo addition reactions.

Isolation: Benzyne is strained and highly reactive due to the nature of its triple bond. In normal acetylenic species (e.g., ethyne) the unhybridized p-orbital are parallel to one another above and below the molecular axis. This facilitates maximum orbital overlap. In benzyne, the electrons are in sp2 hybrids to accommodate the triple bond within the ring system.

Trapping: benzyne can be trapped by dienes, such as furan.

The most prominent aryne reaction is Diels-Alder reaction with dienes.

Aim: To form benzyne and then trap with a number of dienes (Diels-Alder reaction).

Diels-Alder reaction is a conjugate addition where reaction of a conjugated diene with an alkene (dienophile) produces a cyclohexene. Due to the high degree of regio- and stereo selectivity (due to the concerted mechanism), the Diels-Alder reaction is a very powerful reaction and is widely used in synthetic organic chemistry. The reaction is thermodynamically favourable due to the conversion of 2 π-bonds into 2 new stronger σ-bonds.

Procedure: Benzyne is generated by diazotization of anthranilic acid using isoamyl nitrate in 1,2-dimethoxyethane as a solvent. The intermediate compound formed will be benzenediazonium-2-carboxylate which eliminates N2 and CO2 thus producing benzyne. Benzyne (a powerful dienophile) immediately undergoes reaction with furan to give 1,4-dihydronapthalene-1,4-endoxide (Diels-Alder adduct).

1. Introduction

Benzene1,2:

Benzene is a petroleum product, originally manufactured from coal tar, which is used as a component in multiple industrial and consumer products.

Benzene is an aromatic organic chemical compound with molecular formula C6H6, discovered and isolated by Michel Faraday in 1825 from crude oil and named it as Carburetted hydrogen, which has equal number of carbons and hydrogens. August Wilhelm von Hofmann isolated benzene from coal tar and used the word aromatic to designate the benzene family, because of their characteristic smells, relatively inert. Benzene’s highly polyunsaturated structure, with one hydrogen atom for each carbon, was challenging to determine. Friedrich August Kekulé suggested that the structure of benzene was a regular hexagon with a hydrogen atom at each corner, later he changed his suggestion and treated benzene as a mixture of cyclohexatrienes in rapid equilibrium (resonance).

Finally scientists have given a best representation for the structure of benzene, that is indeed hexagonal with each C-C bond length being identical (140pm) and intermediate distance was explained by electron (p-orbital from each neighbouring C overlap) which extends around the ring giving added stability and decreased reactivity.

Structure 1: Structure of benzene

Many important chemicals are derived from benzene by replacing one or more of its hydrogen or carbon atoms with another functional group.

The compound C6H4, which is referred as 'Benzyne', is formally derived from benzene by removal of a pair of adjacent hydrogen atoms and the formation of a triple bond.

1.2 The chemistry of arynes3,4 :

In chemistry, an aryne is an uncharged reactive intermediate derived from an aromatic system (benzene) by removal of two ortho substituents leaving two orbitals with two electrons distributed between them. Benzyne is a general class of reactive intermediates known as 2arynes.

Arynes can undergo three types of mechanisms:

Nucleophilic aromatic substitution

Cyclo addition reactions

Formal [2+2] additions to alkenes

A Nucleophilic aromatic substitution:

Nucleophilic aromatic substitution is an addition-elimination reaction that requires at least one substituent which is strongly electron-withdrawing by resonance to stabilise the anionic addition intermediate.

Some reactions explained by elevating a benzyne intermediate (J.D. Roberts. 1953):

In the below reaction chlorobenzene, having an isotopic labelled carbon atom gives substitution product (aniline-labelled carbon jumbled between two isotopes) and the reaction proceeds through a symmetrical intermediate benzyne, in which two anilines were equivalent.

Reaction 1: Formation of benzyne from Chlorobenzene

Reaction 2: Formation of benzyne from Fluorobenzene.

2 Cycloaddition Reactions:

Cycloaddition reactions are those in which two or more unsaturated molecules combine with the formation of a cyclic adduct.

In the below example aryne intermediates are generated and then undergoes further reaction.

Reaction 3: Formation of benzyne from halosubstutedbenzene.

For many synthetic applications of arynes it is necessary to generate the reactable intermediate under mild conditions. These behave as intermediates in many organic syntheses.

Applications of arynes:

Synthesis of an Aporphine alkaloid

Synthesis of Ellipticene, an anti-cancer alkaloid

Synthesis of a Lysergic Acid N,N-Diethylamide (i.e. LSD) precursor etc.

1.3 Benzyne5,6,24:

Benzyne is the parent molecule of aryne (-yne = triple bond) compounds, derivative of benzene, produced by abstraction of two hydrogen atoms especially one produced by abstraction from neighbouring atoms to form a formal triple bond. Benzyne is a reactive intermediate in some reactions involving benzene compounds. More specifically, it is often found as a result of an elimination reaction with substituted aromatic compounds like halogenated or acylated benzene rings.

The lifetime of benzyne (gas phase) is 20 nanoseconds (2 x 10-8 seconds)

Benzyne is very reactive and rapidly dimerise.

Structure 2: Benzyne

Elimination of the substituent, often by nucleophilic attack, results in a carbocation. This electronic arrangement, due to its instability, causes spontaneous (or base-assisted in the case of hydrogen) elimination of adjacent substituents resulting in a benzene ring with a triple bond.

Reaction 4: Formation of benzyne from Bromobenzene

In the above mechanism benzyne can be derived from halobenzene but this reaction needs a strong base such as NaNH2, BuLi. This reagent undergoes elimination reaction to form benzyne intermediate which traps nucleophilic species.

Another possible mechanism is the abstraction of a group such as hydrogen resulting in a carbanion which causes the elimination of an adjacent group. Both mechanisms result in the formation of a benzyne intermediate.

Reaction 5: Formation of benzyne intermediate.

In the above reaction diazotization of 2–aminobenzoic acid was carried out by using nitrous acid resulting a diazonium salt, which is not isolated, but allowed to undergo loss of CO2 and N2 to generate benzyne.

1.4 Resonance structure of Benzyne 6,7,8,9:

The ability to predict and control the outcome of chemical and biological reactions frequently requires knowledge of the key reaction intermediates and aromatic biradicals.

Benzyne exists by resonance structure 1 and 2 more accurate depiction is 3.

Structure3: Resonance structures of Benzyne.

1,2-didehydrobenzyne (ortho-benzyne-1), 1,3-didehydrobenzyne ( (meta-benzyne-2), and 1,4-didehydrobenzyne ( Para-benzyne -3) are detected as reactive intermediates in full range of organic chemistry.

1.5 Structure existence:

Early investigations focused on their possible existence. O-benzyne was discovered by Roberts classic experiment in 1956 as a reactive intermediate in the ‘‘nucleophilic substitution’’ of halo benzenes. M-benzyne was discovered by Washburns while the Trapping and Para position was discovered later.

Structure 4: Ortho, Meta, Para Benzyne.

O-benzyne < M-benzyne < P-benzyne is the aromatic order and characterization is done by infrared spectroscopy.

The linear geometry of a benzyne has two sp–hybridized carbon atoms having a triple bond between them and the third bond showing side overlapping of two sp2 orbitals, which indicates it cannot be incorporated into a six-membered ring. Possible structures can exist as singlet diradical (electrons spin paired), triplet diradical (parallel spin) or a charge separated species. The presence of a week sigma bond in the structure of benzyne making it as a highly reactive intermediate.

1.6 Diels alder reaction10, 11, 12, 22:

Diels-Alder reaction became a very powerful reaction since 1932 for unsaturated six-membered rings. This synthesis is widely used in synthetic organic chemistry due to the high degree of regio and stereo selectivity of benzyne and is explained by the overlap between the highest occupied molecular orbital of the diene and the lowest unoccupied molecular orbital. This reaction is thermodynamically favourable because of its conversion of 2 π-bonds into new stronger 2 σ-bonds.

GENERAL DIELS-ALDER REACTION:

A dienophile (double bond) adds to a conjugated diene to form an unsaturated six-membered ring. Nearly all conjugated dienes react with appropriate dienophiles.

Reaction 6: Diels-Alder reaction.

Mechanism

Exact mechanism of the Diels Alder reaction was unknown, however the researchers revealed three main ideas on how the mechanism occurs, which are based on the following three studies.

The mechanism is concentrated and synchronous.

2) The mechanism is concentrated and asynchronous.

This reaction is stepwise, first with the formation of a rate determining single bond, which is followed by a faster formation of a second bond.

Benzyne Formation and the Stepwise Decomposition of Benzenediazonium-2-carboxylate and trapping 12,13;

Common usage of the benzyne product involves a Diels–Alder Cyclo addition reaction. Reacting a diene with benzyne taking the place of normal alkene resulting in a bicyclic compound, one ring being benzene, the other being the product of the Diels-Alder reaction.

Diazotisation of anthranilic acid is a common method to produce benzyne and substituted benzynes after the loss of nitrogen and carbon dioxide from the neutral diazonium salt. Benzenediazonium-2-carboxylate may be generated in situ from anthranilic acid by diazotisation in an aprotic medium, or by the removal of the elements of hydrogen chloride from 2-carboxybenzenediazoniumchloride. Benzenediazonium-2-carboxylate is a violently explosive benzyne precursor.

Decomposition reactions of benzenediazonium- 2 - carboxylate by using a number of mixed nucleophilic solvents show number of pathways.

Reaction 7: Decomposition of benzyne.

Benzyne formation is favoured in halogenated solvents and occurs by the concentrated loss of nitrogen and carbon dioxide.

Reaction 8: Formation of benzyne.

2. Instrumentation:

1.7 INFRARED SPECTROSCOPY14:

Infrared spectroscopy is used for the identification and structural analysis of organic compounds. In the infrared region, absorption of electromagnetic radiation occurs due to changes in the vibrational energy of the molecules. 4000cm-1 to 200cm-1 spectra range called as mid-infrared region. The energy of infrared radiation influences on molecular vibrations and rotational transitions. A molecule can only absorb energy, if there is a change in dipole moment of the molecule and thus giving a complex absorption spectrum characteristic of the functional group (finger print) present in the molecule and it is also used for identifying impurities in the compound.

For quantitative analysis, the band intensities of the infrared spectrum are related to the concentration and path length of solution following Beer-Lamberts law.

Substance was crushed in a mortar to make a fine powder and mixed further with nujol to make a slurry. It was rubbed on glass disc and placed in a chamber for analysis.

FT-IR spectra were recorded on a PerkinElmer Paragon 1000 FT-IR and Processing software, Copyright © 2005 PerkinElmer Instruments LLC.

1.8 GAS CHROMATOGRAPHY-MASS SPECTROSCOPY (GC-MS)15:

GC-MS is an analytical method used for separation and identification of small molecules in a mixture. The GC-MS instrument consists of two parts.

Gas Chromatogram,

Mass Spectrometry.

Gas chromatography separates compounds based on their volatility and thermal stability. The temperature of GC column increases at a steady predefined rate with relatively inert gas flowing through forcing the sample along, as the sample was heated in the oven the more reactive compounds begin to vaporise. Therefore the more volatile a compound is the sooner it would elute from the GC column.

The mass analyser works by first bombarding the separated compound with electrons, thus gives the molecules a charge and create fragments, after which a quadruple mass selector maybe used to select a range of desired mass to charge ratios(m/z), or to maintain a set of default criteria. The final stage is detecting the compound using a mass analyser.

2mg of substance was dissolved in 10ml of light petroleum and filled in a labelled vial and placed in the instrument for the analysis.

Mass spectra were recorded using a varian CP-3800 Gas Chromatography with Varian 1200L Quadrupole mass spectrometer.

1.9 NUCLEAR MAGNETIC RESONANCE SPECTROMETRY16:

NMR is a technique using for identification and structural analysis of organic compounds. Absorption of radiation in the radio frequency region of electromagnetic spectrum results in charges in the orientation of spinning nuclei in a magnetic field. Spin quantum number is allocated to all the nuclei which may be zero, half integral or integral, but NMR spectrum can only be achieved with those which contain a non zero value. Because of the charge on the nucleus, spinning about its own axis produces a magnetic moment (µ) along the axis. The frequency at which the energy can be absorbed for an isotope is determined by the relative values of µ and I (angular momentum).The value of µ also determines the sensitivity of the technique for a particular nucleus. The relative sensitivity of 1H is high when comparing to carbon and oxygen isotopes which have spin quantum numbers of zero and therefore they are inactive. For these reasons 1H magnetic resonance is very sensitive for use in analysing the structure of the decomposed products from benzyne.

3mg of substance was taken in a vial and dissolved it in CDCl3 using sonicator. 1% of tetramethyl silane (TMS) was added and made the volume up to 5cm in a nmr tube.

All NMR spectra were recorded at 400 MHz (1H) on a Jeol Eclipse+ 400 NMR spectrometer using Jeol Delta version 4.3.6 control and processing software, copyright © 1990-2006 Jeol USA, Inc. Chemical shifts are reported in ppm, downfield from chloroform-d(CDCl3) as an internal reference.

3 MATERAILS17:

The chemicals and solutions that were used in this synthesis are mostly obtained from Sigma- Aldrich. These chemicals and solvents were used without any further purification.

Name of the chemical

Batch and serial number

Manufactured by

Anthranilic acid

2-(H2N)C6H4CO2H

Mol.Wt

137.14

A1506

Sigma-Aldrich

Isoamyl nitrite

(CH3)2CHCH2CH2ONO

Mol. Wt117.15

F59160

Fluka

1,2-dimethoxyethane

CH3OCH2CH2OCH3

Mol. Wt 90.12

A259527

Sigma-Aldrich

Furan

C4H4O

Mol. Wt 68.07

F47990

Fluka

Tetraphenylcyclopentadienone

C29H20O

Mol. Wt 384.47

T25801

Sigma-Aldrich

Sodium hydroxide

S8045

Sigma-Aldrich

Petroleum ether

F24538

Fluka

Table 1: Explaining about chemicals used in the synthesis.

4 METHOD10:

Two methods were carried out to derive the benzyne. The methods are as follows:

Formation of benzyne and trapping with furan.

Formation of benzyne and trapping with tetraphenylcyclopentadienone.

A Formation of benzyne and trapping with furan19

Furan (10 ml), 1, 2-dimethoxyethane (10 ml) were taken in a 100 ml round bottomed flask, some bumping stones were added. The round bottomed flask was fitted to a reflux condenser and the solution was heated under steam. Mean while, two solutions were prepared in 25ml Erlenmeyer flasks first one containing iso-amyl nitrite (4 ml) made up to 10ml with 1,2-dimethoxyethane and second solution containing anthranilic acid (2.74 gm) with 1,2-dimethoxyethane. 2ml of each solution was added by using separate Pasteur pipettes through the condenser to the round bottom flask under steam with 8-10 min intervals. The solution turned to a dark orange colour after the solutions were fully added. Then the mixture was refluxed for 30min, on cooling this mixture to room temperature a dark brown mixture was precipitated out.

In the mean time NaOH (0.1 M) solution was prepared and added to dark brown mixture. The mixture was then transferred to 100ml separating funnel, organic layer was separated by extracting the product with 15ml petroleum ether. This procedure was repeated for three times to get efficient organic solution. The organic mixture was washed with 6×15ml of distilled water. Then the organic solution was dried over magnesium sulphate (drying agent) and it was removed by suction. Finally the solution was decolourized with active charcoal powder, the solution was taken into rotatory-evaporator to obtain colour less crystalline slurry by applying room temperature and pressure. Crystalline slurry obtained was repurified by sublimation using ice cold petroleum ether.

The melting point of the crystalline compound was determined and the compound was analysed by IR (Nujol), GC-MS, NMR (1H).

Optional step19:

Treatment of 1, 4-dihydronaphthalene-1, 4-endoxide with acid:

1,4-dihydronaphthalene-1,4-endoxide (432 gm) was placed in 25ml Erlenmeyer flask and dissolved in ethanol (10 ml), concentrated HCl (5 ml) was added to the solution and placed at room temperature for one hour. After one hour the mixture was poured into 100ml separating funnel, by adding diethyl ether (20 ml). Extraction of the organic layer was carried out by shaking the separating funnel. Then the organic mixture was washed with 2×15 ml of distilled water. Then the organic solution was dried over magnesium sulphate (drying agent), the drying agent was removed by suction. Finally the solution was decolourized with active charcoal powder. Then the colourless solution was put into rotatory-evaporator to obtain crystalline slurry by applying room temperature and pressure. Crystalline slurry obtained was repurified by sublimation using ice cold petroleum ether.

The melting point of the crystalline compound was determined and the compound was analysed by IR (Nujol), GC-MS.

B Formation of benzene and trapping with tetracyclopentadienone10:

Tetraphenylcyclopentadienone (0.3 M), 1, 2-dimethoxyethane (DME) were placed in 100ml round bottom flask fitted with an efficient reflux condenser and the solution was heated further under steam. On the other hand two solutions were prepared in 25ml Erlenmeyer flasks first one containing iso-amyl nitrite (4 ml)made up to 10ml with 1,2-dimethoxyethane and second solution containing anthranilic acid (2.74 gm) with 1,2-dimethoxyethane. 2 ml of each solution were added by using separate Pasteur pipettes through the condenser to the round bottom flask under steam with 8-10 min intervals. The solution turned in to a dark orange colour after the solutions were fully added. Then the mixture was refluxed for 30 min, on cooling the mixture to room temperature a dark brown mixture was precipitated out.

In the Mean time NaOH (0.1 M) solution was prepared and added to dark brown mixture. And the mixture was transferred to 100 ml separating funnel, organic layer was separated by extracting the product with petroleum ether (15 ml). This procedure was repeated for three times to get efficient organic solution. Again the organic mixture was washed with 6 x 15 ml distilled water. Then the organic solution was dried over magnesium sulphate (drying agent) and it is removed by suction. Finally the solution was decolourized with active charcoal powder. Then the colourless solution was put into rotatory-evaporator to obtain yellow crystalline slurry by applying room temperature and pressure. Crystalline slurry obtained was repurified by sublimation using ice cold petroleum ether.

The melting point of the crystalline compound was determined and the compound was analysed by IR (Nujol), GC-MS.

5 RESULTS AND DISCUSSION:

The obtained solid products from the above three procedures were analysed to know whether the desired compound was formed or not by various analytical techniques.

And these results are compared with that of the literature reference.

Melting point19;

Products

Melting points range(in 0C)

1,4-dihydro-1,4-epoxynaphthalene

53.5-55.5

1-naphthalenol

94-95

1,2,3,4-tetraphenylnaphthalene

200-201

Table 2: Explain about the products melting point range

Melting point literature value of 1, 4-dihydro-1,4-epoxynaphthalene is 54- 570C

Melting point literature value of 1-naphthalenol is 94-960C

Melting point literature value of 1, 2, 3, 4-tetraphenylnaphthalene is 202-2040C

Yield Calculations

1,4-dihydronaphthalene-1,4-endoxide:

Practical percentage yield = (Mass obtained /Theoretical mass) x 100

= (0.932 / 2.88) x 100

= 32.4 %

1,2,3,4-tetraphenyl naphthalene:

Practical percentage yield = (Mass obtained /Theoretical mass) x 100

= (2.15 / 3.03) x 100

= 71.0 %

IR SPECTRA OF THE PRODUCTS14

Infrared spectroscopy is a reliable means of identifying different functional groups present on the product by their characteristic vibration frequency and comparing it with the groups present in the starting material.

1,4-dihydronaphthalene-1,4-endoxide:

Figure 1: IR Spectra of 1,4-dihydronaphthalene-1,4-endoxide.

The FT-IR spectrum obtained for the compound showed the peak at 2923.8cm-1 which was due to Nujol. This was further confirmed from the peaks 1462.8 cm-1 and 1377 cm-1. The peak 1729.7cm-1 might be due to carbonyl group present in the compound.

There are other peaks obtained which may be due to the presence of impurities or solvent.

1-Naphthalenol:

Figure 2: IR Spectra of 1-Naphthalenol.

The FT-IR spectrum of the compound was obtained. The peak at 3417.5 cm-1 clearly showed ‘OH’ stretch. The peak was strong and broad. The peak at 2359.7cm-1 may be due to atmospheric carbon dioxide. Prominent peaks were obtained for Nujol at 2925.7 cm-1, 2853 cm-1, 1482.8 cm-1 and 1377 cm-1.

1,2,3,4-tetraphenyl naphthalene:

Figure 3: IR Spectra of 1,2,3,4-tetraphenylnaphthalene.

According to the FT-IR spectrum of the compound the peaks obtained clearly showed aromatic C-C at 1688.6 cm-1 and 1597.1 cm-1. The peaks at 2957.3cm-1, 1453.4 cm-1 and 1377.1 cm-1 were due of Nujol.

GC-MS SPECTRA OF THE PRODUCTS20

The gas chromatography-mass spectrometry is a combination of two techniques, where gas chromatography separates different components in the sample and mass spectra provides the structural details by fragmentation of the sample.

1,4-dihydronaphthalene-1,4-endoxide

Figure 4: GC-MS Spectra of 1,4-dihydronaphthalene-1,4-endoxide.

Structure 5: Fragmentation of 1,4-dihydronaphthalene-1,4-endoxide.

Fragment

mass-to-charge ratio(m/z)

C10H8 (M+)

144

C10H8+

128

C8H6O+

118

C9H7+

115

C7H5+

89

Table 3: Interpretation of GC-MS results Of 1,4-dihydro-1,4-epoxynaphthalene.

The full scan default mode with selected ions at m/z 89,115,118,128and 144, was shown in above graph. As it can be seen in the figure, sample was well separated in a run time of 7-7.5 min, and the spectra showing last peak at 144 (m/z)..

From the spectra, if we observe the molecular peak at 144 m/z (last peak) and comparing it with the molecular weight of the desired product, and also verifying it with reference library search ensured that this spectra of the compound is almost nearer to reference spectra.

Hence I conclude that the product is reliable with the desired product.

1,2,,3,4-Tetraphenylnaphthalene

Figure 5: GC-MS Spectra of 1,2,3,4-Tetraphenylnaphthalene.

Structure 6: Fragmentation of 1,2,3,4-Tetraphenylnaphthalene.

Fragment

mass-to-charge ratio(m/z)

C34H24 (M+)

432

C28H19+

355

C12H24+

156

C6H5+

77

Table 4: Interpretation of GC-MS results of the 1,2,3,4-Tetraphenylnaphthalene.

The full scan default mode with selected ions at m/z 77,156,355and 432, was shown in above graph. As it can be seen in the figure, sample was well separated in a run time of 25.5-26.5 min, and the spectra showing most abundant peak at 432 (m/z) following 26 min retention time. But between 20-26min of retention time so many other benzene compounds were eluted which may be due to the reaction mixture or handling procedures.

The fragmentation of 1,2,3,4-tetraphenylnaphthalene, it showed loss of phenyl rings from the attached naphthalene ring, simultaneously spectra showing peaks at m/z 355,156,77 respectively.

From the spectra, if we observe the molecular peak at 432 m/z, comparing it with the molecular weight of the desired product, and also verifying it with reference library search ensured that this spectra of the compound is almost nearer to reference spectra

Hence I conclude that the product is reliable with the desired product.

Nuclear magnetic resonance –proton spectroscopy21:

Figure 6: NMR spectrum of 1,4-dihydronaphthalene-1,4-endoxide.

Structure 7: Symmetric structure of 1,4-dihydronaphthalene-1,4-endoxide.

δ (ppm)

Multiplicity

Coupling constant J in (hertz)

Integrals

7.26

Doublet of doublet

5.03,3.3

2H

7.0234

Doublet of doublet

1.10,0.92

2H

6.97

Doublet of doublet

5.13,2.93

2H

5.7094

Doublet of doblet

-

2H

Table 5: Interpretation of NMR results of the 1,4-dihydronaphthalene-1,4-endoxide.

The 'H NMR spectra was obtained by using CDCl3 as solvent and spectra can explain the structure of the compound by showing chemical shift of functional groups.

From the above structure of 1,4-dihydro-1,4-epoxynaphthalene contains symmetrical structure and showing four different types of doublet protons which are indicated as Ha, Ha, Hb , Hb, Hc, Hc, Hd, Hd, and having equal integration ratio, The spectra of 1,4-dihydro-1,4-epoxynaphthalene showing that all the four protons are attached to the epoxy naphthalene base and located in same environment and strongly deshielded by the π orbitals of the ring and absorbed in the low field, ranging from 5.7094ppm-7.2695ppm. While, the protons Ha, Hb, Hc, Hd showing the multiplication at 6.9439-6.9874, 7.2260-7.2695, 5.7094, 7.0103-7.0332 respectively. And all these doublets are having one neighbouring protons. Ha, Hb, Hc, Hd are respective of neighbouring protons Hb, Hc, Hd, Ha and showed a signal that split into a doublet. Each proton on the structure had two neighbouring protons which indicates one proton is non-equivalent and the other is equivalent and gives a signal that is split into a doublet of doublet.

All the peaks in Ha, Hb, Hc, Hd mostly similar and remaining peaks were found between 1.219ppm-5.2038ppm which may be due to the impurities or the small changes in the local shielding environment of the CHCl3 induced by the solute via intermolecular interactions.

6 Conclusion:

Formation and trapping of benzene has been successfully done by using two different trapping agents which are Furan and tetraphenyl cyclopentadienone with significant results.

In the first experiment, benzyne was trapped by furan and the adduct obtained was 1,4-dihydronaphthalene-1,4-endoxide. The yield obtained in the first experiment was low when compare to the second experiment. The compound synthesised was crystalline in nature and yellow orange in colour. The compound was confirmed by its melting point, Infrared, GC-MS and NMR Spectra compared with that of the literature values.

Similarly the benzene was also trapped by using 1, 2, 3, 4-tetraphenylcyclopentadienone. Here, the adduct obtained was 1, 2, 3, 4-tetraphenylnaphthalene. The compound was dark brown in colour and crystalline in nature. It was also confirmed by comparing the obtained melting point values with the literature values.

7 Further work:

Even though the positive results were achieved in both methods, but that may not be enough to describe or explore the formation and trapping of benzyne with dienes. In my view the formation and trapping of benzyne can also be done by using anthracene by following the Diels-Alder reaction.

The cycloaddition of substituted furans to the diterpenoid aryne, generates by in situ diazotization of the anthranilic acid. The product characterization is done by GC-MS, IR, and NMR etc.

Future work: Thus by following the above procedure benzyne can be formed by trapping with a number of dienes (eg; Tetracyclene, Anthracene) by Diels-Alder reaction.


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