Glutathione seems to play an important role by protecting against benzene-induced DNA breaks and it is being identified as a new biomarker for exposure and effect. [99] Benzene leaked into the Songhua River, which supplies drinking water to the city, after an explosion at a China National Petroleum Corporation (CNPC) factory in the city of Jilin on 13 November 2005. It took several years to assign a structural formula to benzene because of its unusual stability and peculiar properties. According to the experiments, the single (CC) and double (C = C) covalent bonds have a bond length of 0.154 nm and 0.134 nm, respectively. Structure of benzene is a controversial topic because benzene has outstanding characteristics. In the year 1834, a German chemist naming Eilhardt Mitscherlich heated the benzoic acid with lime, which produced benzene. The purpose of establishing an IDLH value is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted [NIOSH 2004[82]]. In nitration, benzene reacts with nitronium ions (NO2+), which is a strong electrophile produced by combining sulfuric and nitric acids. Benzene is an organic chemical compound with the molecular formula C6H6. Benzene is classified as a carcinogen, which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure. Trimerization of acetylene gives benzene. Although a major industrial chemical, benzene finds limited use in consumer items because of its toxicity.[13]. Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline. The structure of benzene has been of interest since its discovery. (This estimate assumes no threshold for benzene's carcinogenic effects.) The six carbon atoms form a perfectly regular hexagon. In bacteria, dioxygenase enzyme can add an oxygen to the ring, and the unstable product is immediately reduced (by NADH) to a cyclic diol with two double bonds, breaking the aromaticity. Two sp 2 -hybrid orbitals of each C-atom overlap with two sp 2 -hybrid orbital of two other C-atoms to form sigma bonds. Benzene shows 2 resonating structures. Under these conditions, toluene undergoes dealkylation to benzene and methane: This irreversible reaction is accompanied by an equilibrium side reaction that produces Claus, Adolph K.L. As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. The inhalation of benzene vapours causes irritation to the eyes and upper respiratory tract. [20] Four years later, Mansfield began the first industrial-scale production of benzene, based on the coal-tar method. Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. Benzene. Outdoor air may contain low levels of benzene from automobile service stations, wood smoke, tobacco smoke, the transfer of gasoline, exhaust from motor vehicles, and industrial emissions. This intermediate distance is consistent with electron delocalization: the electrons for C–C bonding are distributed equally between each of the six carbon atoms. Kekulé based his postulation on the following premises: The molecular formula for benzene is C 6 H 6. Due to the chemical formula, benzene is categorized as a hydrocarbon. Benzene structure. Benzene and cyclohexane have a similar structure, only the ring (of delocalized electrons) inside Benzene distinguishes it from cyclohexane. In benzene, the atoms are hydrogens. To accurately reflect the nature of the bonding, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms. Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in the urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. In the United States, concern over its negative health effects and the possibility of benzene's entering the groundwater have led to stringent regulation of gasoline's benzene content, with limits typically around 1%. The chemical formula for benzene is C6H6, i.e it has 6 hydrogen- H atoms and six-carbon atoms and has an average mass of about 78.112. Due to its characteristic properties and unusual stability, the determination of the actual structure of benzene took many years. [100][101], This article is about the chemical compound. In 1872, Kekulé suggested that benzene had two complementary structures and that these forms rapidly interconverted, so that if there were a double bond between any pair of carbon atoms at one instant, that double bond would become a single bond at the next instant (and vice versa). Therefore, between the carbon atoms of benzene there were no fixed (i.e., constant) and distinct single or double bonds; instead, the bonds between the carbon atoms were identical. biphenyl (aka diphenyl) at higher temperature: If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen. It behaves both as saturated and unsaturated hydrocarbon. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Rover's Latest Discovery Puts It 'On the Table, "Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars", "Unicode Character 'BENZENE RING' (U+232C)", "Unicode Character 'BENZENE RING WITH CIRCLE' (U+23E3)", "Heterocyclic Chemistry: Heterocyclic Compounds", "Market Study: Benzene (2nd edition), Ceresana, August 2014", "Market Study: Toluene, Ceresana, January 2015", "Control of Hazardous Air Pollutants From Mobile Sources", "Traffic-related air pollution and the onset of myocardial infarction: disclosing benzene as a trigger? This was 7 years after he had solved the problem of how carbon atoms could bond to up to four other atoms at the same time. Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane, hexane, which has 14. In 2005, the water supply to the city of Harbin in China with a population of almost nine million people, was cut off because of a major benzene exposure. In heterocycles, carbon atoms in the benzene ring are replaced with other elements. The aromatic products of the reaction are then separated from the reaction mixture (or reformate) by extraction with any one of a number of solvents, including diethylene glycol or sulfolane, and benzene is then separated from the other aromatics by distillation. Benzene is one of the most commonly known aromatic compounds with chemical formula C6H6. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment [NIOSH 2004]. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL) is not disputed to be caused by benzene. This means that every carbon atom is capable of chemical bonds with four other atoms. Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia, bone marrow abnormalities and cardiovascular disease. Given that demand for para-xylene (p-xylene) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. Sulfonation of benzene involves the use of oleum, a mixture of sulfuric acid with sulfur trioxide. Pure benzene, for example, oxidizes in the body to produce an epoxide, benzene oxide, which is not excreted readily and can interact with DNA to produce harmful mutations. The next year he published a much longer paper in German on the same subject. These p orbitals overlap, delocalizing the six electrons and making benzene a fully conjugated system. The structural representation of benzene is as shown in the figure below. The carbon atoms are represented by a corner that is bonded to other atoms. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported. The molecular formula of benzene is C 6 H 6. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake seizing its own tail (this is a common symbol in many ancient cultures known as the Ouroboros or Endless knot). How benzene affects human health depend on how much and how long a person is exposed to it. X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). [38] If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862. very informative article of benzyne. Kekulé was the first to suggest a sensible structure for benzene. This discovery led to the production of Sanka. With the global phaseout of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. 11,960) for the fractional distillation of coal tar. [80] These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. Its … The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. [63] In many European languages, the word for petroleum or gasoline is an exact cognate of "benzene". Benzene has been recognized as a toxic substance that causes acute and chronic health problems. Das Benzol." Here Kekulé spoke of the creation of the theory. The chemical formula for benzene is C6H6, i.e it has 6 hydrogen- H atoms and six-carbon atoms and has an average mass of about 78.112. Benzene was historically used as a significant component in many consumer products such as Liquid Wrench, several paint strippers, rubber cements, spot removers, and other products. CYP2E1 is involved at multiple steps: converting benzene to oxepin (benzene oxide), phenol to hydroquinone, and hydroquinone to both benzenetriol and catechol. In the 19th and early 20th centuries, benzene was used as an after-shave lotion because of its pleasant smell. Most people in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. KEKULE STRUCTURE OF BENZENE. Benzene is an aromatic hydrocarbon with the molecular formula, C 6 H 6 {{\text{C}}_{\text{6}}}{{\text{H}}_{\text{6}}} C 6 H 6 It acts as the parent compound for the production of numerous aromatic organic compounds. [34] Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. It is a colorless liquid with a characteristic odor. Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma around petrol (gasoline) stations. Benzene have similar shape with cyclohex… Via the reaction the diazonium compound with hypophosphorus acid aniline gives benzene. The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). In catalytic reforming, a mixture of hydrocarbons with boiling points between 60–200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Benzene is made up of six atoms of carbon and six atoms of hydrogen. There are alternate single and double bonds and one hydrogen is … Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Although of no commercial significance, many other routes to benzene exist. See: Kolmetz, Gentry, Guidelines for BTX Revamps, AIChE 2007 Spring Conference. 6-membered aromatic rings with one carbon replaced by another group: This page was last edited on 4 January 2021, at 09:31. Structure of Benzene: Kekule benzene: two forms are in rapid equilibrium 154 pm 134 pm • All bonds are ~139 pm (intermediate between C-C and C=C) • Electron density is distributed evenly between the six carbons • Structure is planar, hexagonal • C–C–C bond angles are 120° • … Birch reduction, a non catalytic process, however selectively hydrogenates benzene to the diene. NQ01 mutations result in loss of function and may result in decreased detoxification. As its toxicity became obvious, benzene was supplanted by other solvents, especially toluene (methylbenzene), which has similar physical properties but is not as carcinogenic. The structure has a six-carbon ring which is represented by a hexagon and it includes 3-double bonds. [97], Under specific conditions and in the presence of other chemicals benzoic acid (a preservative) and ascorbic acid (Vitamin C) may interact to produce benzene. Benzene structure was found by Kekule in 1872. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the REL (10-hour) of 0.1 ppm. Replacement of a second CH bond with N gives, depending on the location of the second N, pyridazine, pyrimidine, or pyrazine. Agency for Toxic Substances and Disease Registry. The formulas and structure reveal benzene as a pure aromatic hydrocarbon, wherein it is also defined as a compound composing hydrogen & carbon having alternate double bonds in the form of the ring. The formation of a single product revealed a lot about the aromatic hydrocarbon; it was concluded that all the carbon and hydrogen of benzene were identical. [76], OSHA regulates levels of benzene in the workplace. Skin contact with solvents containing benzene causes dry, itching, cracked and fissured skin. One way of understanding the carcinogenic effects of benzene is by examining the products of biological oxidation. The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding the recommended (8-hour) exposure limit of 0.1 ppm.[78]. Structure of the benzene molecule. Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to the relatively rapid removal of the chemical by exhalation or biotransformation. [75], Exposure to benzene may lead progressively to aplastic anemia, leukaemia, and multiple myeloma. In this process, the xylene stream exiting the TDP unit is approximately 90% p-xylene. Structure of benzene Kekulé ModelConsists of a ring of carbon atoms containing alternating single and double bonds (3 double bonds and 3 single bonds). The chemical formula for benzene is. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. A circle is used as an alternative symbol inside the hexagon that is used to represent six pi electrons. [39], The cyclic nature of benzene was finally confirmed by the crystallographer Kathleen Lonsdale in 1929. Benzene is a naturally occurring substance produced by volcanoes and forest fires and present in many plants and animals, but benzene is also a major industrial chemical made from coal and oil. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency. The short term exposure limit for airborne benzene is 5 ppm for 15 minutes. It is said to be highly toxic in nature and is also known as a carcinogen; which exposure to this may lead to leukemia. The pathway for the metabolism of benzene is complex and begins in the liver. Toluene disproportionation (TDP) is the conversion of toluene to benzene and xylene. [79] This regulation is based on preventing benzene leukemogenesis. This process was later discontinued. [96], Inhaled benzene is primarily expelled unchanged through exhalation. Its structure and some of the properties are as follows. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. [18] In 1836, the French chemist Auguste Laurent named the substance "phène";[19] this word has become the root of the English word "phenol", which is hydroxylated benzene, and "phenyl", the radical formed by abstraction of a hydrogen atom (free radical H•) from benzene. (1867) "Theoretische Betrachtungen und deren Anwendungen zur Systematik der organischen Chemie" (Theoretical considerations and their applications to the classification scheme of organic chemistry). [12], Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. In 2013, the biggest consumer country of benzene was China, followed by the USA. Eventually, the presently accepted structure of a regular-hexagonal, planar ring of carbons was adopted, and the exceptional thermodynamic and chemical stability of this system was attributed to resonance stabilization of a conjugated cyclic triene. A typical reaction yield exceeds 95%. Benzene has 2 resonance structures but taken individually none show the delocalisation of electrons and they can exist at the same time as electrons are delocalised. The affected batches were removed from sale. The American Petroleum Institute (API) stated in 1948 that "it is generally considered that the only absolutely safe concentration for benzene is zero". Nitrobenzene is the precursor to aniline. Benzoic acid and its salts undergo decarboxylation to benzene. [69][89], Genetic polymorphisms in these enzymes may induce loss of function or gain of function. Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon. [21][22] Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. [46], Trace amounts of benzene are found in petroleum and coal. The solvent-properties of the two are similar, but toluene is less toxic and has a wider liquid range. The double bonds within this structure are mainly separated by a single bond, hen… In the case of benzene, the hybrid structure is the one below (the one you learn at school): The formulas and structure reveal benzene as a pure. The Kekulé structure for benzene, C 6 H 6. This intermediate distance is caused by electron delocalization: the electrons for C=C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms – fewer than the corresponding parent alkane, hexane. Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. According to this theory, all the C-atoms in benzene are sp 2 -hybridized. The limit of the fusion process is the hydrogen-free allotrope of carbon, graphite. Your email address will not be published. [71] The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. The double bonds within this structure are mainly separated by a single bond, hence this arrangement is recognized to have conjugated double bonds. From p. 102: " … benzene, according to this view, may be represented by a double ring, in fact." The ratio of carbon to hydrogen in Benzene is the same. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Resonance forms or resonating structures only differ in arrangement of electrons. [52] The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures. The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating the twenty-fifth anniversary of his first benzene paper. Benzene, also known as benzol, is an organic chemical compound with the formula C 6 H 6.It is a colorless and flammable liquid with a sweet smell. Die aromatischen Verbindungen. Thiele, Johannes (1899) "Zur Kenntnis der ungesättigten Verbindungen" (On our knowledge of unsaturated compounds). The aromatic compounds. The real structure is an intermediate of these structures represented by a resonance hybrid. Chlorination is achieved with chlorine to give chlorobenzene in the presence of a Lewis acid catalyst such as aluminium tri-chloride. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium, molybdenum, or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. The carbon atoms are represented by a corner that is bonded to other atoms. Benzene (C₆H₆) was first isolated by Michael Faraday in 1825. Benzene is harmful especially to the tissues that form blood cells. In fact, when benzene is reacted to produce different derivatives, it ceases to be the compound benzene, and the chemical properties of the products can often be completely different. [65] Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in the presence of a strong Lewis acid catalyst. Via hydrogenation, benzene and its derivatives convert to cyclohexane and derivatives. ), pp. Benzene was discovered in the year 1825 by Michael Faraday in illuminating gas. [16][17] In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin) and lime. Benzene causes cancer in animals including humans. As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. In 1855, Hofmann used the word "aromatic" to designate this family relationship, after a characteristic property of many of its members. Toluene hydrodealkylation converts toluene to benzene. Benzene is used mainly as an intermediate to make other chemicals, above all ethylbenzene, cumene, cyclohexane, nitrobenzene, and alkylbenzene. So, resonance structure of benzene differs only in arrangement of electrons, number of carbon atoms and hydrogen atoms in benzene remain same. NQ01 metabolizes benzoquinone toward polyphenols (counteracting the effect of MPO). All the carbons have … Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps. The Nazis used benzene administered via injection as one of their many methods of killing. Approximately 24,700,000 tons were produced in 1999. Today, most benzene comes from the petrochemical industry, with only a small fraction being produced from coal. Because of its chemical formula, C 6 H 6, benzene is classified as a hydrocarbon, which is a compound that consists of only carbon and hydrogen atoms. What is the Kekulé structure? [92] Benzene metabolism involves enzymes coded for by polymorphic genes. In 1845, Charles Mansfield, working under August Wilhelm von Hofmann, isolated benzene from coal tar. This reaction is practiced on a large scale industrially. COVID-19 is an emerging, rapidly evolving situation. Benzene shows resonance as it has more than one way to place double bonds in the ring. GSH is involved with the formation of phenylmercapturic acid. I have learned a lot. It contains eight hydrogen atoms less than the corresponding parent hydrocarbon, i.e., hexane (C 6 H 14 ). This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts, such as finely divided nickel. This structure was accepted for many years however during this period many new pieces of evidence arose questioning Kekulé’s model of Benzene leading to the eventual proposal of a new model regarding the structure of Benzene. Benzene (C6H6), simplest organic, aromatic hydrocarbon and parent compound of numerous important aromatic compounds. Required fields are marked *, Benzene is one of the most commonly known aromatic compounds with chemical formula, The structural representation of benzene is as shown in the figure below. After exposure to 63 to 405 mg/m3 of benzene for 1 to 5 hours, 51 to 87% was excreted in the urine as phenol over a period of 23 to 50 hours. The word "benzene" derives from "gum benzoin" (benzoin resin), an aromatic resin known to European pharmacists and perfumers since the 16th century as a product of southeast Asia. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated the production of benzene from petroleum. In March 2006, the official Food Standards Agency in Britain conducted a survey of 150 brands of soft drinks. Benzene is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives. The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee. The compound appears like a colourless liquid having a characteristic odour. When benzene was discovered, it was found to yield only a single monosubstituted product. ChEBI CHEBI:16716 A six-carbon aromatic annulene in which each carbon atom donates one of its two 2p electrons into a delocalised pi system. Derivatives of benzene occur sufficiently often as a component of organic molecules that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds,[57] and U+23E3 (⏣) for a delocalized version.[58]. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating. Benzene is one of the organic and simplest aromatic hydrocarbon and the parent compound of which has about a numerous number of important aromatic compounds. In benzene, the atoms are hydrogens. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. Structure of the Benzene Molecule. It found that four contained benzene levels above World Health Organization limits. Benzene | C6H6 | CID 241 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety/hazards/toxicity information, supplier lists, and more. [36] Some historians have suggested that the parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. In a human study 16.4 to 41.6% of retained benzene was eliminated through the lungs within five to seven hours after a two- to three-hour exposure to 47 to 110 ppm and only 0.07 to 0.2% of the remaining benzene was excreted unchanged in the urine. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes. Even if it is not a common substrate for metabolism, benzene can be oxidized by both bacteria and eukaryotes. It is a compound consisting of only hydrogen and carbon atoms. The geometry of each carbon is trigonal planar: (2007). Delocalised ModelConsists of the sideways overlap of p-orbitals of all six of the carbon atoms forming π-bonds (rings of delocalised electrons) above and below the plane of carbon atoms. Benzene is hepatically metabolized and excreted in the urine. According to molecular orbital theory, benzene ring involves the formation of three delocalized π – orbitals spanning all six carbon atoms, while the valence bond theory describes two stable resonance structures for the ring. Benzene is a colourless liquid with a characteristic odour and is primarily used in the production of polystyrene. Benzene is a carcinogen that also damages bone marrow and the central nervous system. The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. Benzene is widely utilized chemicals that are involved in various manufacturing products that we use daily such as plastics, detergents, and rubber. The Structure and Geometry of Benzene All the carbon atoms in benzene are sp 2 hybridized connected by sp2 – sp2 single bonds and each has a p orbital perpendicular to the plane of the atoms.