{"id":22733,"date":"2022-01-19T13:10:25","date_gmt":"2022-01-19T07:40:25","guid":{"rendered":"https:\/\/infinitylearn.com\/surge\/?p=22733"},"modified":"2025-02-28T16:14:17","modified_gmt":"2025-02-28T10:44:17","slug":"hydrocarbons-class-11-notes-chemistry-chapter-13","status":"publish","type":"post","link":"https:\/\/infinitylearn.com\/surge\/study-materials\/hydrocarbons\/class-11-notes\/chemistry\/chapter-13\/","title":{"rendered":"Hydrocarbons Class 11 Notes Chemistry Chapter 13"},"content":{"rendered":"<h2>Hydrocarbons Class 11 Notes Chemistry Chapter 13<\/h2>\n<p><strong>\u2022 Hydrocarbon: <\/strong>A compound of carbon and hydrogen is known as a hydrocarbon.<br \/>\n<strong>\u2022 Saturated Hydrocarbon: <\/strong>A hydrocarbon is said to be saturated if it contains only C\u2014C single bonds. For example Ethane CH<sub>3<\/sub>\u2014CH<sub>3 <\/sub><br \/>\n<strong>\u2022 Unsaturated Hydrocarbon<\/strong><\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32798125785_898456d944_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-1\" width=\"687\" height=\"67\" \/><br \/>\n<strong>\u2022 Aromatic Hydrocarbon: <\/strong>Benzene and its derivatives are called aromatic compounds.<br \/>\nExample:<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32757902126_904f6d00a6_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-2\" width=\"216\" height=\"118\" \/><br \/>\n<strong>\u2022 Alicyclic Compounds: <\/strong>Cyclic compounds which consist only of carbon atoms are called alicyclic or carbocyclic compounds.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32798125655_89d85083fd_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-3\" width=\"367\" height=\"76\" \/><br \/>\n<strong>\u2022 Heterocyclic Compounds: <\/strong>Cyclic compounds in which the ring atoms are of carbon and some other element (For example, N, S, or O) are called heterocyclic compounds.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32798125595_1ac9c7c8b7_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-4\" width=\"230\" height=\"87\" \/><br \/>\n<strong>\u2022 Alkanes: <\/strong>Alkanes are the simplest organic compounds made of carbon and hydrogen only.<br \/>\nThey have the general formula C<sub>n<\/sub>HC<sub>2n+2<\/sub> (where n = 1, 2, 3, etc.)<br \/>\nThe carbon atoms in their molecules are bonded to each other by single covalent bonds. Since the carbon skeleton of alkanes is fully saturated\u2019 with hydrogens, they are also called saturated hydrocarbons. Alkanes contain strong C \u2014C and C \u2014H bonds. Therefore, this class of hydrocarbons are relatively chemically inert. Hence they are sometimes referred to as paraffin (Latin parum affinis = little affinity). The first three members of this class can be represented as<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016823_b882184599_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-5\" width=\"485\" height=\"119\" \/><br \/>\n<strong>Structure:<\/strong><\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32645004672_788f6a5c9a_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-6\" width=\"191\" height=\"185\" \/><br \/>\nIn methane, carbon forms single bonds with four hydrogen atoms. All H\u2014G\u2014H bond angles are 109.5\u00b0. Methane has a tetrahedral structure. C\u2014C and C\u2014H bonds are formed by head-on overlapping of sp<sup>3<\/sup> hybrid orbitals of carbon and Are orbitals of hydrogen atoms.<br \/>\n<strong>\u2022 Nomenclature Guidelines<\/strong><br \/>\nUse the following step-by-step procedure to write the IUPAC names from the structural formulas. Consider the following structural formula:<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016703_4688ea85f9_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-7\" width=\"330\" height=\"73\" \/><br \/>\n<strong>Step 1.<\/strong> Identify the longest chain: In the given example, the longest chain has seven carbons. The seven carbon chain is heptane.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32645004622_6036078367_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-8\" width=\"471\" height=\"126\" \/><br \/>\n<strong>Step 2.<\/strong> Number the chain: The chain is numbered from left to right. This gives the lowest numbers to the attached alkyl group.<br \/>\n<strong>Step 3.<\/strong> Identify the alkyl group: There are two methyl groups at C-2 and C-3, there is one ethyl group of C-4.<br \/>\nStep 4. Write the IUPAC name: In this case, the IUPAC name is 4-Ethyl-2,3-dimethyl heptane. Always keep in mind (a) Numbers are separated from each other by commas. (b) Numbers are separated from names by hyphens, (c) Prefixes di, tri is not taken into account in alphabetising substituent names.<br \/>\n<strong>\u2022 Newman Projections<\/strong><br \/>\nIn this projection, the molecule is viewed at the C\u2014C bond head-on.<br \/>\n<img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016573_b352b1963c_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-9\" width=\"396\" height=\"266\" \/><br \/>\n<strong>\u2022 Relative Stability of Conformations<\/strong><br \/>\nIn the staggered form of ethane, there are maximum repulsive forces, minimum energy and maximum stability of the molecule. On the other hand, when the staggering form changes in the eclipsed form the electron clouds of the carbon-hydrogen bonds come closer to each other increasing electron cloud repulsions, molecule have to possess more energy and thus has lower stability.<br \/>\nTorsional Angle: The magnitude of torsional strain depends upon the angle of rotation about the C\u2014C bond. This angle is also called a dihedral angle or torsional angle.<br \/>\n<strong>\u2022 Alkenes<\/strong><br \/>\nAlkenes are hydrocarbons that contain a carbon-carbon double bond (C=C) in their molecule.<br \/>\nThey have the general formula<br \/>\n<strong>Structure:<\/strong><br \/>\nLet us consider (H<sub>2<\/sub>C=CH<sub>2<\/sub>) for illustrating the orbital make-up of alkenes.<br \/>\nIn ethylene the carbon atoms are sp<sup>2<\/sup> hybridized- They are attached by a bond and a \u03c3 bond.<br \/>\nThe bond results from the overlap of two sp<sup>2<\/sup> hybrid orbitals. The \u03c0 bond is formed from the overlap of the unhybridized p-orbitals. Ethylene is a planar molecule.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32645004572_e4f753b156_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-10\" width=\"381\" height=\"237\" \/><br \/>\n<strong>Points to be noted<\/strong><br \/>\n(i) The carbon-carbon double bond in alkenes is made up of one \u03c3 and one \u03c0-bond.<br \/>\n(ii) Alkenes are more reactive than Alkanes. This is due to the availability of n electrons.<br \/>\n<strong>\u2022 Nomenclature<\/strong><br \/>\nIn IUPAC system<br \/>\n(i) The name of the hydrocarbon is based on the parent alkene having the longest \u2018 carbon chain of which double bond is apart.<br \/>\n(ii) This chain is numbered from the end near the double bond and its position is indicated by the number of the carbon atom not which the double bond originates,<br \/>\n(iii) The name of the parent alkene with the position number of the double bond is written first and then the names of other substituents are prefixed to it.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016363_ba8eda05a6_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-11\" width=\"241\" height=\"359\" \/><br \/>\n(iv) When there are two or three double bonds in a molecule, the ending-one of the corresponding alkane is replaced by-a diene to get the name.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32645004502_c46529be98_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-12\" width=\"208\" height=\"70\" \/><br \/>\n<strong>\u2022 Isomerism<\/strong><br \/>\nStructural Isomerism: Ethene and propene have no structural isomers, but there are three structures of butenes.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016173_e2f048f074_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-13\" width=\"244\" height=\"209\" \/><br \/>\nOf these, two are straight-chain structures with the difference being in the position of the double bond in the molecules.<br \/>\nThese are position isomers and the third structure is a branched-chain isomer.<br \/>\nGeometrical Isomerism: It is known that a carbon-carbon double bond is made up of one \u03c3 bond and one \u03c0-bond. The \u03c0-bond presents free rotation about the double bond.<br \/>\nThis presentation of rotation about the carbon-carbon double bond gives rise to the phenomenon of geometrical isomerism. An alkene having a formula RCH=CHR can have two stereoisomers, depending upon whether the two alkyl groups are on the same or opposite sides of the double bond. If they are on the same side, then it is called cis-isomer. If they are on opposite sides, then it is called trans-isomer.<br \/>\nDue to the different arrangements of atoms or groups in space, these isomers differ in their properties like melting point, boiling point, dipole moment, solubility, etc.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984016063_83dfb05a4b_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-14\" width=\"305\" height=\"135\" \/><br \/>\n<strong>\u2022 Alkynes<\/strong><br \/>\nAlkynes are characterised by the presence of a triple bond in the molecule.<br \/>\nTheir general formula is C<sub>n<\/sub>H<sub>2n-2<\/sub>.<br \/>\nThe first and the most important member of this series of hydrocarbons is acetylene, HC=CH, and hence they are also called the Acetylenes.<br \/>\n<strong>Structure:<\/strong> Let us consider ethyne (HC=CH) for illustrating the orbital make-up of ethyne. In ethyne, the carbon atoms are sp hybridized. They are attached by a \u03c3-bond and two \u03c0-bonds.<br \/>\nThe \u03c3 -bond results from the overlap of two sp hybrid orbitals. The \u03c0 bonds are formed from the separate overlap of the two p-orbitals from the two adjacent carbon atoms.<br \/>\nThe other sp hybrid orbital of each carbon atom forms a \u03c3 bond with another carbon or hydrogen atom. Ethyne is a linear molecule.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32645004362_2d3ce6315a_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-15\" width=\"749\" height=\"315\" \/><br \/>\n<strong>Points to be noted:<\/strong><br \/>\n(i) The carbon-carbon triple bond in alkynes is made up of one \u03c3 and two \u03c0 bonds.<br \/>\n(ii) Like alkenes, alkynes undergo an addition reaction. These reactions are due to the availability of more exposed \u03c0 electrons.<br \/>\n<strong>\u2022 Nomenclature<\/strong><br \/>\n<strong>IUPAC System:<\/strong> The IUPAC names of alkynes are obtained by dropping the ending-ane of the parent alkane and adding the suffix-ya. The carbon chain including the triple bond is \u2013 numbered from the end nearest this bond. The position of the triple bond is indicated by prefixing the number of carbon preceding it to the name of the alkyne.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32675147031_548a3b12cc_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-16\" width=\"386\" height=\"123\" \/><br \/>\n<strong>Preparation:<\/strong><br \/>\n<strong>From calcium carbide:<\/strong> Ethyne is prepared by treating calcium carbide with water. Calcium carbide is prepared as follows:<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31955171284_59ddcfe384_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-17\" width=\"334\" height=\"91\" \/><br \/>\n<strong>From vicinal dihalides<\/strong>: When reacted with vicinal dihalides, alcoholic potassium hydroxide undergo dehydrohalogenation. One molecule of hydrogen halide is eliminated to form alkenyl halide which on treatment with sodamide gives alkyne.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32675147021_3993c532c5_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-18\" width=\"477\" height=\"185\" \/><br \/>\n<strong>\u2022 Aromatic Hydrocarbons<\/strong><br \/>\nThese hydrocarbons are also known as \u2018arenes\u2019. Most of such compounds were found to contain a benzene ring.<br \/>\nAromatic compounds containing benzene rings are known as benzenoids and those not containing a benzene ring are known as non-benzenoids. Some examples of arenes are given below.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32798125055_e310cccd7b_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-19\" width=\"271\" height=\"210\" \/><br \/>\nNomenclature and Isomerism: Benzene and its homologous are generally called by their common names which are accepted by the IUPAC system. The homologous benzene having a single alkyl group is named Alkyl benzenes.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417797430_0334af1d6a_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-20\" width=\"663\" height=\"362\" \/><br \/>\n<strong>Structure of Benzene:<\/strong> By elemental analysis, it is found that the molecular formula of benzene is C<sub>6<\/sub>H<sub>6<\/sub>. This indicates that benzene is a highly unsaturated compound. In 1865, Kekule gave the cyclic planar structure of benzene with six carbons with alternate double and single bonds.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32798124905_7dc3e62be3_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-21\" width=\"258\" height=\"125\" \/><br \/>\nThe Kekule structure indicates the possibility of two isomeric 1,2-bromobenzene. In one of the isomers, the bromine atoms are attached to the doubly bonded carbon atoms whereas in the other they are attached to the singly bonded carbon.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417796970_11f4ee456c_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-22\" width=\"223\" height=\"93\" \/><br \/>\nOnly one ortho-bromobenzene could be prepared.<br \/>\nTo overcome this problem Kekule suggested that benzene was a mixture of two forms.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31955170444_11f4ee456c_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-23\" width=\"205\" height=\"82\" \/><br \/>\n<strong>Failure of Kekule\u2019s structure:<\/strong> Kekule structure of benzene failed to explain the unique stability and its preference to substitution reaction than addition reactions.<br \/>\n<strong>Resonance Structure of Benzene:<\/strong> The phenomenon in which two or more structures can be written for a substance that involves identical positions of atoms is called resonance. In benzene\u2019s, Kekule\u2019s structures (1) and (2) represent the resonance structures. The actual structure \u2013 of the molecule is represented by a hybrid of these two structures.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417796560_63e594d730_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-24\" width=\"328\" height=\"81\" \/><br \/>\n<strong> Orbital structure of benzene:<\/strong> All six carbon atoms in benzene are sp<sup>2<\/sup> hybridized. The sp<sup>2<\/sup> hybrid orbitals overlap with each other and with s orbitals of the six hydrogen atoms forming C\u2014C and C\u2014H \u03c3-bonds.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31955170284_dc678b8e77_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-25\" width=\"266\" height=\"254\" \/><br \/>\nX-ray diffraction data indicate that benzene is a planar molecule. The data indicate that all the six C\u2014C bond lengths are of the same order (139 pm) which is intermediate between (C\u2014C) single bond (154 pm) and C\u2014C double bond (133 pm). Thus the presence of pure double bond in benzene gives the idea of the reluctance of benzene to show addition reaction under normal conditions. The is, It explains the unusual behaviour of benzene.<br \/>\n<strong>Aromaticity:<\/strong> It is a property of the sp<sup>2<\/sup> hybridized planar rings in which the p orbitals allow cyclic delocalization of \u03c0 electrons.<br \/>\n<strong>Conditions for Aromaticity:<\/strong><br \/>\n(i) An aromatic compound is cyclic and planar.<br \/>\n(ii) Each atom in an aromatic ring has a p orbital. These p orbitals must be parallel so that a continuous overlap is possible around the ring.<br \/>\n(iii) The cyclic \u03c0 molecular orbital (electron cloud) formed by the overlap of p orbitals must contain (4n + 2) \u03c0 electrons. Where n = integer (0, 1, 2, 3, etc.). This is known as the Huckel rule.<br \/>\nSome Examples of Atomic Compounds are given below:<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417796160_d7181c247a_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-26\" width=\"495\" height=\"134\" \/><br \/>\n<img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417796000_abd2ca8c12_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-27\" width=\"308\" height=\"267\" \/><br \/>\n<strong>Preparation of Benzene:<\/strong> Benzene is commercially isolated from coal tar. However, some synthetic methods are applied in the laboratory for the preparation of benzene.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31955170024_8dba47df6d_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-28\" width=\"685\" height=\"384\" \/><br \/>\n<strong>Physical Properties of Benzene:<\/strong><br \/>\n(i) Benzene is a colourless liquid.<br \/>\n(ii) It is\u2019 insoluble in water. It is soluble in alcohol, ether, chloroform etc.<br \/>\n(iii) Benzene itself is a good solvent for many organic and inorganic substances e.g., fat, resins, sulphur and iodine.<br \/>\n(iv) It bums with a luminous, sooty flame in contrast to alkanes and alkenes which usually bum with a bluish flame.<br \/>\n<strong>Chemical Properties:<\/strong><br \/>\nBenzene undergoes the following types of chemical reactions.<br \/>\n(i) Electrophillic Substitution Reaction<br \/>\n(ii) Addition Reaction<br \/>\n<strong>Electrophillic Substitution Reactions:<\/strong><\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32417795690_3a4cf6eba9_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-29\" width=\"600\" height=\"456\" \/><\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32675146621_877b939407_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-30\" width=\"564\" height=\"511\" \/><br \/>\nBenzene on treatment with an excess of chlorine in the presence of anhydrous AlCl<sub>3<\/sub> can be chlorinated to hexachlorobenzene (C<sub>6<\/sub>Cl<sub>6<\/sub>)<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984014993_8f6c15fe19_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-31\" width=\"428\" height=\"178\" \/><br \/>\n<strong> Mechanism of electrophilic substitution reactions:<\/strong><br \/>\nAll electrophilic substitution reactions follow the same three-step mechanism.<\/p>\n<p><strong>Step 1.<\/strong> Formation of an electrophile:<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32675146571_dc5201528a_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-32\" width=\"411\" height=\"250\" \/><br \/>\n<strong>Step 2.<\/strong> The electrophile attacks the aromatic ring to form a carbonium ion.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/32675146541_57ed010bfc_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-33\" width=\"567\" height=\"356\" \/><br \/>\n<strong>Step 3.<\/strong> Loss of proton gives the substitution product.<\/p>\n<p><strong>Activating groups:<\/strong> This group activates the benzene ring for the attack by an electrophile. Example, \u2014OH; \u2014NH<sub>2<\/sub>, \u2014NHR, \u2014NHCOCH<sub>3<\/sub>, \u2014OCH<sub>3<\/sub> \u2014CH<sub>3<\/sub> \u2014C<sub>2<\/sub>H<sub>5<\/sub> etc.<\/p>\n<p><strong>Deactivating groups:<\/strong> Due to deactivating group because of the strong \u2014I effect, overall electron density on benzene ring decreases. It makes further substitution difficult.<\/p>\n<p><strong>Metadirecting group:<\/strong> The groups which direct the incoming group to meta position are called meta directing groups. Some examples of meta directing groups are \u2014N0<sub>2<\/sub>, \u2014CN, \u2014CHO, \u2014COR, \u2014COOH, \u2014COOR, -S0<sub>3<\/sub>H etc.<\/p>\n<p>Let us consider the example of the nitro group: Since the Nitro group due to its strong -I effect reduces the electron density in the benzene ring. Nitrobenzene is a resonance hybrid of the following structures.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31984014833_2917a6b328_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-34\" width=\"591\" height=\"157\" \/><br \/>\n<strong>Carcinogenicity and Toxicity:<\/strong> Some polynuclear hydrocarbons containing more than two benzene rings fused become toxic and they are having cancer-producing properties. They are formed due to incomplete combustion of some organic materials like tobacco, coal and petroleum, etc.<br \/>\nSome of the carcinogenic hydrocarbons are given below.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter\" src=\"https:\/\/infinitylearn.com\/surge\/wp-content\/uploads\/2021\/12\/31955169264_1edbf1843b_o.png\" alt=\"hydrocarbons-cbse-notes-for-class-11-chemistry-35\" width=\"493\" height=\"465\" \/><br \/>\n<strong>\u2022 Hydrocarbons:<\/strong> They are compounds of carbon and hydrogen only.<br \/>\nOpen Chain saturated compound\u2014Alkane<br \/>\nUnsaturated Compound\u2014Alkenes and Alkynes Aromatic Compound\u2014Benzene and its derivatives Terminal alkynes are weakly acidic.<\/p>\n<p><strong>\u2022 Conformation:<\/strong> Spatial arrangements obtained by rotation around sigma bonds.<\/p>\n<p><strong>\u2022 Eclipsed Conformation:<\/strong> Less stable because of more repulsion between bond pairs of electrons.<\/p>\n<p><strong>\u2022 Staggered:<\/strong> It is more stable since there is less repulsion between bond pairs of electrons.<\/p>\n<p><strong>\u2022 Geometrical isomerism:<\/strong> Observed only in compounds containing a double bond.<\/p>\n<p><strong>\u2022 Stability of benzene.<\/strong> This is explained based on resonance hybrid.<\/p>\n<p><strong>\u2022 Arenes:<\/strong> Take part in an electrophilic substitution reaction.<br \/>\nAromaticity is determined by Huckle\u2019s rule (4n + 2) rule.]\n<p>For more visit <a href=\"https:\/\/infinitylearn.com\/surge\/chsmistry\/notes\/surface-chemistry-class-12-notes-chemistry-chapter-5\/\">Surface Chemistry Class 12 Notes Chemistry Chapter 5<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Hydrocarbons Class 11 Notes Chemistry Chapter 13 \u2022 Hydrocarbon: A compound of carbon and hydrogen is known as a hydrocarbon. 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