Structure of Benzene - Discovery, Lewis Structure, Properties, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:45 PM IST

Introduction: What is Structure of Benzene

Benzene is said to be an organic chemical compound containing carbon and hydrogen. The molecular formula of benzene is C₆H₆. This suggests that benzene is composed of six carbon atoms and six hydrogen atoms. These atoms are joined together in a planar ring and to each carbon atom, one hydrogen atom is attached. The benzene structural formula can be drawn in the following manner:

This Story also Contains

Introduction: What is Structure of Benzene
Discovery of Benzene
Properties and Occurrence of Benzene
Uses of Benzene

Structure of Benzene - Discovery, Lewis Structure, Properties, FAQs

Structure of benzene

In an alternate position, it contains double bonds; this double bond shows that benzene is unsaturated in nature. Those compounds which contain double or triple bonds are said to be unsaturated in nature while those who have only a single bond are saturated in nature. Benzene is also kept in the category of hydrocarbons, these compounds are made up of carbon and hydrogen only.

Benzene formula or benzene chemical formula is C₆H₆.

C₆H₆ the chemical name is benzene.

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Discovery of Benzene

Benzene was discovered by European pharmacists in the 16^th century and the word benzene is basically derived from the word gum benzoin or we can call it benzoin resin which is known as aromatic resin. Aromatic compounds have ring-like structures. Benzene is said to be aromatic in nature and the aromaticity concept can also be explained with the help of Huckel’s rule this rule states that a compound that contain electrons is aromatic in nature, In the case of benzene n = 1 and it contains electrons i.e. aromatic in nature.

Structure

Benzene structure contains six carbon bonds and six hydrogen bonds with alternating double bonds. According to X-ray diffraction, all the six carbon-carbon bonds are of equal length and it is measured to be 140 picometers. There is a slight difference between double and single carbon-carbon bonds. The C-C double bond is greater in length as compared to a single C-C bond this difference can be explained on the basis of delocalization as in the case of double bond electrons are equally distributed to all the six carbon atoms.

Benzene and cyclohexane almost contain similar structures, the only difference is the loss of one hydrogen per carbon in the ring of delocalized electrons which makes it a different kind of cyclohexane. The shape of the molecule is said to be of planar nature. The molecular orbital of benzene generally involves the formation of three delocalized electrons which revolves around all six carbon atoms and gives resonating structures. Resonating structures involve the revolution of double bonds and it gives two stable resonating structures. The resonating structures of benzene can be shown as follows:

The resonating structures of benzene.

It is said to be highly stable in nature and due to its chemical properties, these are aromatic in nature. The nature of the bonding of benzene is exactly described with the cyclic hexagonal shape of six carbon atoms.

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Lewis Structure of Benzene

The Lewis structure of any compound is shown by the valence shell electrons of that molecule. It generally tells us the arrangement of electrons in a molecule with the help of dot representation and can also be known as electron dot structure. In this type of structure, each bond is shown with the help of two dots between two atoms.

Lewis structure of benzene can be derived by using a number of steps given follow:

1. First step generally involves the determination of the total number of valence electrons of every atom present in benzene and it can be calculated by combining the valence electrons of carbon and hydrogen.

Valence electrons are those electrons that are present in the valence shell of that atom.

Number of carbon atoms in benzene = 6

Valence electrons in carbon = 4

Carbon has atomic number 6 so electron distribution in K, L shell is 2, 4 and in the outermost shell L shell which is its valence shell contains 4 electrons which correspond that it has valency 4.

Number of hydrogen atoms in benzene = 6

Valence electrons in hydrogen = 1

An atomic number of hydrogen is 1 so it contains valence electrons in the outermost shell and has valency 1.

Now, the Total number of the valence electrons in carbon =

Total number of the valence electrons in hydrogen =

2. Now determine the total number of valence electrons in benzene

Total number of valence electrons in benzene = Total number of valence electrons in carbon + Total number of valence electrons in hydrogen

= 24 + 6 = 30 electrons.

3. Step 3 involves the need for electrons to complete their octet

In the case of carbon 6 electrons are divided into two subshells K and L, subshell K contains 2 and electrons and L contains 4 electrons, here in this case K subshell is already filled and L have 4 electrons this corresponds that L subshell needs 4 more electrons to complete its octet. In the case of a hydrogen atom, it contains only 1 electron which is filled in K subshell and it contains at most 2 electrons so hydrogen needs only 1 electron to complete its octet. This corresponds to each carbon atom forming a single bond with one hydrogen atom.

Electron Dot structure of benzene can be shown as:

Lewis dot structure of benzene

In this case, hydrogen atoms are paired but each carbon atom will need 3 more electrons for its outermost shell.

4. Number of electrons needed to acquire stable configuration

Now, according to the structure given in point 3, it is clear that each carbon atom needs 3 more electrons to complete its octet and there are 6 carbon atoms in benzene so as to total it needs 18 electrons to attain a stable configuration. This corresponds to the remaining electrons being placed in such a manner that it completes the octet of a carbon atom. The final dot structure of benzene can be shown in the following manner:

Dot structure of benzene representing the valence electron.

Like in this case 2 dots correspond to a single bond while 4 dots correspond to double bond atoms. This gives us the true structure of the benzene atom which contains alternative double bonds.

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5. Lewis structure of benzene

This information tells us that benzene contains six carbon atoms attached in a planar ring with alternate double and single bonds and each carbon is attached to one hydrogen atom with the help of a single bond. structure of benzene can be shown as:

Lewis structure of benzene.

We can also show this structure in three-dimensional form which can be shown as:

Three dimensional structure of benzene.

This can also be shown as a normal aromatic ring or like cyclohexane structure with the presence of double bonds this can be shown as:

Benzene structure

Properties and Occurrence of Benzene

Benzene is said to be highly flammable in nature. It is said to be a volatile compound and has a gasoline-like smell. It can be found in the oil-refining process as a side product along with crude oil. It can also be found by naturally occurring substances like a forest fire which is present in plants and animals. It is a clear and colorless liquid. The molar mass of benzene is 78.11 g/mol and slightly soluble in water but easily soluble in organic solvents. Its density is less than water.

Uses of Benzene

Benzene has a number of industrial uses like it is used in the preparation of phenol, aniline which is further used in dyes, and dodecylbenzene in detergents. In the preparation of other chemicals like ethylbenzene, cyclohexane, alkylbenzene, nitrobenzene etc. It can also use in the manufacturing of nylon fibers.

Benzyne

Benzyne is the main substituent derived from benzene; it is said to be a highly reactive species that are derived from the aromatic ring by removal of two substituents and it contains a triple bond. The structure of the benzyne atom can be shown as follows:

Benzyne structure

The molecular formula of benzyne is .

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Frequently Asked Questions (FAQs)

1. Who explain the structure of benzene?

The structure of benzene has been explained by Joseph Loschmidt (in 1861) and August Kekule von Stradonitz (in 1866). They independently proposed a cyclic arrangement of six carbons with alternating single and double bonds.

2. Benzene is said to be saturated or unsaturated in nature?

Benzene is said to be unsaturated in nature as it contains double bond in it.

3. What is the difference between cyclohexane and benzene?

Benzene is said to be an organic compound represented by the chemical formula C₆H₆and have a planar structure whereas cyclohexane is a cyclic molecule having molecular formula C₆H₁₂. Benzene is an aromatic compound and shows the aromatic character as it has a conjugated pi-electron system and follows Huckel’s rule. It is a cyclic conjugated compound. Resonance delocalization of ? electrons caused stability of the compound. Cyclohexane is a non-aromatic compound as it does not have a conjugated pi-electron system. It doesn’t obey 4n+2? electron rule.

4. Define benzyne.

Benzyne is the main substituent derived from benzene. It is said to be highly reactive species which is derived from the aromatic ring by removal of two substituents and it contains a triple bond.

5. What is the valency of carbon?

Carbon has atomic number 6 which is divided into two shells called K and L where K contains 2 electrons and L have 4 electrons but it can attain 8 electrons so the valency of carbon is said to be 4 as it needs 4 electrons to fulfill the need of electrons in its outermost shell.

6. What is the shape of benzene ?

The shape of benzene is a planar regular hexagon having a bond angles of 120°. Benzene is a regular hexagon because all the bonds are identical. The delocalization of the electrons means that there aren't alternating double and single bonds.

7. How benzene is formed?

Benzene is formed from ethyne by the process known as cyclic polymerization. In the benzene formation process, Ethyne is passed through a red-hot iron tube at 873 K. The ethyne molecule then undergoes cyclic polymerization to form benzene.

8. What is the historical significance of benzene's discovery?

Benzene's discovery in 1825 by Michael Faraday was significant because it challenged existing theories about organic compounds. Its unique structure and properties led to the development of aromatic chemistry, revolutionizing our understanding of carbon-based molecules.

9. Why was benzene's structure initially puzzling to chemists?

Benzene's structure was puzzling because its empirical formula (CH) suggested it should be highly unsaturated and reactive. However, it displayed unusual stability and didn't behave like typical unsaturated compounds, leading to confusion about its true structure.

10. How did Kekulé's dream contribute to understanding benzene's structure?

August Kekulé reportedly had a dream of a snake biting its own tail, which inspired him to propose the cyclic structure of benzene. This dream led to the concept of a hexagonal ring of carbon atoms, a breakthrough in understanding benzene's structure.

11. What is the significance of the 4n+2 rule in determining aromaticity?

The 4n+2 rule (Hückel's rule) predicts that cyclic, planar molecules with 4n+2 π electrons will be aromatic and thus unusually stable. It explains why benzene (6 π electrons) is aromatic, while cyclobutadiene (4 π electrons) is not.

12. What is the relationship between benzene's structure and its role as a precursor in industrial chemistry?

Benzene's unique structure makes it a versatile starting material in industrial chemistry. Its aromatic character and ability to undergo various substitution reactions make it a key precursor for pharmaceuticals, plastics, dyes, and other materials.

13. What is the significance of the circle inside the hexagon in benzene's structural representation?

The circle inside the hexagon represents the delocalized π electron cloud in benzene. It's a shorthand way to show that the electrons are spread evenly around the ring, rather than fixed in specific double bonds.

14. How does benzene's structure contribute to its planar shape?

Benzene's planar shape results from the sp² hybridization of its carbon atoms. This hybridization creates a flat hexagonal ring with 120° bond angles, allowing maximum overlap of p orbitals for π bond formation.

15. What is the hybridization state of carbon atoms in benzene?

Carbon atoms in benzene are sp² hybridized. This means each carbon has three sp² orbitals in a trigonal planar arrangement and one unhybridized p orbital perpendicular to this plane.

16. How does the Lewis structure of benzene differ from its actual electron distribution?

The Lewis structure shows alternating single and double bonds, but in reality, benzene has six equivalent carbon-carbon bonds. The actual electron distribution is a continuous ring of delocalized π electrons above and below the plane of the molecule.

17. What is meant by the term "delocalized electrons" in the context of benzene?

Delocalized electrons in benzene refer to the π electrons that are not confined to specific carbon-carbon bonds but are instead spread out (or delocalized) over the entire ring structure.

18. Why is benzene more stable than predicted by its Lewis structure?

Benzene is more stable due to resonance stabilization. The delocalization of π electrons across all six carbon atoms lowers the overall energy of the molecule, making it more stable than a hypothetical cyclohexatriene structure.

19. What is aromaticity, and how does benzene exemplify this concept?

Aromaticity is a property of cyclic, planar molecules with delocalized π electrons. Benzene is the quintessential aromatic compound, exhibiting enhanced stability, a planar structure, and following Hückel's rule (4n+2 π electrons).

20. How does the bond length in benzene compare to typical single and double carbon-carbon bonds?

Benzene's C-C bond length (1.39 Å) is intermediate between typical single (1.54 Å) and double (1.34 Å) bonds. This uniformity in bond length is evidence of electron delocalization and equivalent bonds in the ring.

21. What is the significance of benzene's resonance structure?

Benzene's resonance structure, represented by two alternating forms with double bonds, explains its enhanced stability. This concept of electron delocalization is crucial in understanding aromatic compounds and their unique properties.

22. What is Hückel's rule, and how does it apply to benzene?

Hückel's rule states that planar, cyclic molecules with 4n+2 π electrons (where n is a non-negative integer) are aromatic. Benzene, with 6 π electrons (n=1), satisfies this rule and is therefore aromatic.

23. Why is benzene considered the parent compound of aromatic hydrocarbons?

Benzene is considered the parent compound of aromatic hydrocarbons because it is the simplest aromatic ring system. Many other aromatic compounds can be derived by substituting one or more hydrogen atoms on the benzene ring.

24. How does the reactivity of benzene's substituents compare to those on non-aromatic rings?

Substituents on benzene often show different reactivity compared to those on non-aromatic rings. For example, the -OH group in phenol is more acidic than in cyclohexanol due to resonance stabilization of the phenoxide ion.

25. What is the relationship between benzene's structure and its UV-Vis absorption spectrum?

Benzene's UV-Vis spectrum shows strong absorption bands due to its conjugated π electron system. The delocalized electrons can be excited by UV light, resulting in characteristic absorption peaks that reflect its electronic structure.

26. What is the relationship between benzene's structure and its resistance to oxidation?

Benzene's resistance to oxidation is a direct result of its aromatic stability. The delocalized π electron system is energetically favorable, making it difficult for oxidizing agents to disrupt the ring structure.

27. How does the concept of resonance apply to substituted benzene rings?

In substituted benzene rings, resonance structures can show the delocalization of electrons from electron-donating groups into the ring or from the ring into electron-withdrawing groups, affecting the reactivity and properties of the compound.

28. How does the concept of aromaticity in benzene extend to heterocyclic compounds?

The concept of aromaticity extends to heterocyclic compounds that have a cyclic, planar structure with delocalized π electrons. Examples include pyridine and furan, which follow the 4n+2 rule and exhibit aromatic properties similar to benzene.

29. Why does benzene undergo substitution reactions rather than addition reactions?

Benzene prefers substitution reactions because they maintain its aromatic stability. Addition reactions would disrupt the π electron system, leading to a loss of aromaticity and the associated stability.

30. How does the reactivity of benzene compare to that of alkenes?

Benzene is less reactive than alkenes towards addition reactions due to its aromatic stability. While alkenes readily undergo addition, benzene typically undergoes substitution reactions to maintain its aromatic character.

31. How does the heat of hydrogenation of benzene compare to that of cyclohexene?

The heat of hydrogenation of benzene is significantly less than that of cyclohexene. This difference, known as the resonance energy, quantifies benzene's extra stability due to aromaticity.

32. How does the boiling point of benzene compare to alkanes with similar molecular mass?

Benzene has a higher boiling point than alkanes of similar molecular mass. This is due to the planar structure of benzene, which allows for stronger intermolecular π-π stacking interactions.

33. How does the dipole moment of benzene compare to other six-membered ring compounds?

Benzene has a dipole moment of zero due to its symmetrical structure. This is in contrast to other six-membered rings like cyclohexane derivatives, which may have non-zero dipole moments due to uneven electron distribution.

34. How does the acidity of benzene compare to that of alkynes?

Benzene is much less acidic than terminal alkynes. While alkynes can be deprotonated by strong bases, benzene requires extremely strong bases (like organolithium compounds) to remove a proton, due to its aromatic stability.

35. What is the significance of benzene's D6h symmetry?

Benzene's D6h symmetry (6-fold rotational symmetry and 6 mirror planes) reflects its high degree of symmetry. This symmetry is crucial for its properties, including its lack of dipole moment and the equivalence of all carbon-carbon bonds.

36. How does the aromaticity of benzene affect its heat capacity?

The aromaticity of benzene contributes to a higher heat capacity compared to non-aromatic hydrocarbons of similar mass. This is due to the additional energy required to disrupt the delocalized π electron system.

37. What is the relationship between benzene's structure and its ability to conduct electricity?

While benzene itself is not a good conductor, its delocalized π electron system makes it more conductive than saturated hydrocarbons. This property is the basis for the development of conductive polymers based on aromatic systems.

38. How does the presence of substituents affect the aromaticity of benzene?

Most substituents do not significantly affect benzene's aromaticity as long as the cyclic conjugation is maintained. However, some groups can enhance or diminish aromatic character by donating or withdrawing electrons from the ring.

39. What is the significance of benzene's high C:H ratio in its combustion properties?

Benzene's high C:H ratio (1:1) compared to alkanes results in a sooty flame when burned. This is because there's insufficient hydrogen to combine with all the carbon, leading to the formation of carbon particles (soot) during combustion.

40. What is the relationship between benzene's structure and its ability to form charge-transfer complexes?

Benzene's π electron-rich system allows it to form charge-transfer complexes with electron-deficient species. This property is due to the ability of the delocalized π electrons to interact with electron acceptors.

41. How does the reactivity of benzene compare in electrophilic vs. nucleophilic reactions?

Benzene is more reactive towards electrophilic substitution reactions than nucleophilic ones. This is because the π electron cloud is electron-rich and can attack electrophiles, while nucleophiles are repelled by this electron density.

42. What is the significance of benzene's resonance energy in chemical reactions?

Benzene's resonance energy (about 36 kcal/mol) represents the extra stability of the aromatic system. This energy must be overcome for reactions that disrupt aromaticity, explaining benzene's preference for substitution over addition reactions.

43. How does the concept of hyperconjugation apply to substituted benzene rings?

Hyperconjugation in substituted benzenes involves the interaction of σ-bonding electrons (usually from alkyl groups) with the π system of the ring. This can affect the electron distribution and reactivity of the aromatic system.

44. What is the relationship between benzene's structure and its ability to participate in π-π stacking interactions?

Benzene's planar structure and delocalized π electrons allow for π-π stacking interactions between benzene rings. These non-covalent interactions play crucial roles in molecular recognition, crystal packing, and biological processes.

45. How does the aromaticity of benzene influence its magnetic properties?

The ring current in benzene, caused by the circulation of π electrons, generates a magnetic field. This results in anisotropic magnetic effects observable in NMR spectroscopy, where protons inside the ring are shielded and those outside are deshielded.

46. What is the significance of benzene's ability to undergo electrophilic aromatic substitution?

Electrophilic aromatic substitution is a key reaction type for benzene, allowing for the introduction of various functional groups while maintaining aromaticity. This reactivity is fundamental to the synthesis of many aromatic compounds.

47. How does the concept of aromaticity in benzene relate to Frost circles?

Frost circles are a graphical method to predict the stability of cyclic conjugated systems. For benzene, the Frost circle shows that all six π electrons occupy bonding orbitals, confirming its aromatic stability as predicted by Hückel's rule.

48. What is the relationship between benzene's structure and its photochemical properties?

Benzene's conjugated π system allows for electronic transitions upon absorption of UV light. This leads to characteristic photochemical reactions, such as photocyclization, which can be used in organic synthesis and materials science.

49. How does the concept of antiaromaticity relate to benzene's structure?

Antiaromaticity is the opposite of aromaticity, occurring in cyclic compounds with 4n π electrons. While benzene is aromatic and stable, antiaromatic compounds like cyclobutadiene are highly unstable due to their electron configuration.

50. What is the significance of benzene's ability to form metal complexes?

Benzene can form complexes with metals (e.g., chromium tricarbonyl complexes) due to its π electron system. These complexes are important in organometallic chemistry and have applications in catalysis and materials science.

51. How does the aromaticity of benzene affect its reactivity in pericyclic reactions?

The aromaticity of benzene generally makes it less reactive in pericyclic reactions compared to non-aromatic dienes. However, under certain conditions, benzene can participate in reactions like Diels-Alder cycloadditions, often requiring harsh conditions.

52. What is the relationship between benzene's structure and its ability to act as a ligand in organometallic chemistry?

Benzene's delocalized π electron system allows it to act as a ligand in organometallic complexes. It can coordinate to metals in a η6 (eta-6) fashion, where all six carbon atoms interact with the metal center.

53. How does the concept of ring current in benzene relate to its NMR spectroscopy?

The ring current in benzene, caused by the circulation of π electrons, creates a local magnetic field. This field opposes the external field above and below the ring plane, resulting in the characteristic downfield shift of benzene protons in NMR spectroscopy.

54. What is the significance of benzene's ability to undergo radical substitution reactions?

While less common than electrophilic substitution, benzene can undergo radical substitution reactions. This reactivity is important in certain industrial processes and provides an alternative method for functionalizing the benzene ring.

55. How does the concept of aromaticity in benzene extend to polycyclic aromatic hydrocarbons (PAHs)?

The concept of aromaticity extends to PAHs, which consist of fused benzene rings. These compounds exhibit enhanced stability due to extended π electron delocalization across multiple rings, influencing their chemical and physical properties.

56. How does the concept of induced ring current in benzene relate to its diamagnetic anisotropy?

The induced ring current in benzene creates a diamagnetic anisotropy. This means that benzene's magnetic susceptibility is different parallel and perpendicular to the ring plane, a property that can be observed in various spectroscopic techniques.

57. What is the significance of understanding benzene's structure in the context of drug design and medicinal chemistry?

Understanding benzene's structure is crucial in drug design and medicinal chemistry because many drugs contain aromatic rings. The electronic properties, reactivity, and metabolic stability of these aromatic moieties significantly influence a drug's efficacy and pharmacokinetics.