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    This Is How You Tackle Organic Chemistry For JEE Main, NEET

    By Tavneet Bedi
    12 Mar'22  10 min read
    This Is How You Tackle Organic Chemistry For JEE Main, NEET
    Synopsis

    Class 12 Organic Chemistry accounts for a large chunk of questions in JEE Main and NEET exams – for BTech Engineering and Medicine. The NTA JEE Main syllabus and exam pattern have also altered since 2019, placing more emphasis on some parts than others, but broadly, the JEE Main, JEE Advanced and NEET questions from Organic Chemistry can be classified into five types, each one demanding a separate approach. Considering how overwhelming some students find it, here’s an easy way to tackle the subject.

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    This Is How You Tackle Organic Chemistry For JEE Main, NEET
    Synopsis

    Class 12 Organic Chemistry accounts for a large chunk of questions in JEE Main and NEET exams – for BTech Engineering and Medicine. The NTA JEE Main syllabus and exam pattern have also altered since 2019, placing more emphasis on some parts than others, but broadly, the JEE Main, JEE Advanced and NEET questions from Organic Chemistry can be classified into five types, each one demanding a separate approach. Considering how overwhelming some students find it, here’s an easy way to tackle the subject.

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    For many students, the most interesting subsection of Chemistry is Organic chemistry. They can visualise the molecules in action, carrying out a substitution reaction here, an elimination reaction there, and lots of rearrangements in the carbon skeleton caused by different reagents under different reaction conditions. However, not all students share the same enthusiasm and there is a significant chunk which gets confused. They usually try to memorise the products formed in the reactions and face problems because they do not get into the “why” the molecules behave the way they do. The same set of reagents can show a different type of reaction under a different set of reaction conditions and it is not possible to mug up all the reactions.

    A basic example encountered here is that of an alkyl halide with hydroxide ions. Alkyl halides react with hydroxide ions in aqueous solutions to form a substitution product which is an alcohol. The same reaction, when carried out in alcoholic solution, leads to an elimination reaction with an alkene as the end product. This fundamental difference in the behaviour of hydroxide ions can be understood if one is aware of the solvation effect of these solvents. Water causes a more effective solvation of the hydroxide ions, making them milder, while alcohol is not as effective in solvating the anions. This causes the hydroxide ions to be stronger in alcoholic conditions which explains the elimination product. Many also believe that the hydroxide ions also create some amount of alkoxide ions and it is these which cause the elimination. The paper setters for Engineering and Medical entrance exams like the Joint Entrance Examination Main (JEE Main) and National Eligibility cum Entrance Test (NEET) usually check the understanding of these subtle nuances and reaction mechanisms. A lack of understanding can lead to a lot of negative marking in the exam.

    Let us now look at the types of problems asked in the different entrance examinations. These can be classified into the following broad categories:

    1. Problems on General Organic Chemistry

    2. Mechanism-based problems

    3. Stereochemistry-related problems

    4. Name Reactions including tests of different functional groups

    5. Structure based questions

    General Organic Chemistry

    In Class 11 Chemistry, Organic Chemistry is introduced to students through the concepts of General Organic Chemistry. These consist of problems on IUPAC Nomenclature, Isomerism, Electronic Effects, Reaction Intermediates and their stability. These are the building blocks which form the foundation of Organic Chemistry. Understanding these basics is necessary for all the reactions. While there may not be direct questions on these, a student’s grasp of the basics is often tested through questions on multistep synthesis or as an indirect part of problem solving. So, understanding General Organic Chemistry becomes imperative for your preparation. Spend time on identifying the different types of electrophiles and nucleophiles involved in the different reactions, the conditions necessary for their formation, and the factors responsible for stabilising them. Problems involving comparison of Acidic and Basic strengths of different functional groups are also very important as they indirectly tell you the strengths of the different negative charges and how they affect the nucleophilicity and the basicity of the attacking anions.

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    JEE Main, NEET Syllabus: Mechanism-Based Problems

    The next type of problems typically included in JEE Main and NEET is the Mechanism based problem. If understood well, these can seem some of the most logical parts in Chemistry. If ignored, they can lead to an overwhelming feeling of “arbitrariness” in the reactions. This often results in ‘disliking’ and ignoring a section that is otherwise easy to score in.

    The approach to be followed while learning is to ask lots of questions: “What is the mechanism followed in a particular reaction? Does it involve an ionic mechanism or a non-ionic mechanism? Which intermediate is involved in a reaction? Is the intermediate a carbocation, carbanion, carbon free radical or a transition state? What electronic effects stabilise these intermediates? Which electronic effect dominates? What is the preferred solvent in the reaction? Is it a polar or a non polar solvent? What is the rate determining step in a reaction? What factors affect the rate of this rate determining step?” Asking these will help you better understand the effects of each of these parameters on the reactions.

    A major problem faced by students is figuring out which substitution or elimination would be preferred and whether it would follow the unimolecular or the bimolecular path, the classic “tetralemma” between SN1, SN2, E1 and E2 reactions. Unimolecular Reactions (SN1 and E1) are carried out in polar protic solvents with the tertiary halides. Bimolecular reactions (SN2 and E2) are carried out preferably in Polar aprotic solvents. Primary halides undergo bimolecular substitution while secondary and tertiary halides undergo elimination under these reaction conditions. Increasing the strength of the attacking negative charges or an increase in the temperature would lead to an increase in the percentage of elimination products. This would, however, be an oversimplification and a variety of other factors also influence the reactions which must be understood to correctly predict the course of the reaction.

    Another important point to understand is whether the reaction is thermodynamically-controlled or kinetically-controlled. Thermodynamics deals with the stability of the products formed and kinetics deals with the ease of the reaction through an easier and sometimes a less favourable path thermodynamically. Usually the two align but at other times they act in opposite directions and it is usually here when the so-called “exceptions” in Organic Chemistry appear.

    JEE Advanced: Stereochemistry Problems

    Stereochemistry is another important concept which needs to be understood to score well in the Organic Chemistry parts of the JEE Main syllabus and NEET syllabus. This deals with the different spatial arrangements of the groups attached at the chiral centres and also how a different orientation can lead to products having different chemical and physical properties. The first step in dealing with Stereochemistry usually lies in understanding the different methods of projecting the 3D orientations of molecules into 2D (Wedge dash, Sawhorse, Newman, and Fisher projections) and their conversions into one another. There are direct questions on the relative (D/L) and absolute configurations (R/S) which can be answered from these projections. Indirect questions would be on the various stereoselective and stereospecific reactions.

    Some reactions are Stereoselective, meaning a particular stereoisomer having a particular orientation is selectively formed as a major product and the other isomer is formed as a minor product. Some reactions are Stereospecific, meaning only a single specific type of stereochemically active (or inactive) product is obtained. This constitutes a very major chunk of the difficult problems in the JEE Advanced examination, the entrance test for BTech programmes at the Indian Institutes of Technology (IITs). In the exam, understanding of this concept is clubbed with the different reaction mechanisms.

    Some examples can be addition of different reagents to an alkene leading to generation of new chiral centres in products. The alkene can be symmetric or asymmetric, cis or trans. There can be a syn addition, anti addition or addition through the formation of a Carbocation depending upon the type of the reagents used. These, in turn, could lead to an optically active or inactive product mixture. There can be formation of meso compounds or racemic mixtures with symmetric alkenes. Asymmetric alkenes usually form racemic mixtures containing equal amounts of two enantiomeric forms. Enantiomers are optically active individually but an equimolar mixture of two enantiomers causes an equal rotation of the plane polarised light in opposite directions effectively cancelling each other’s effect. These reactions represent a significant chunk of questions asked in the JEE Advanced examination and are quite simple if you understand their mechanisms.

    Name Reactions

    Another significant set of problems in Organic Chemistry are on the Name Reactions. A list of important reactions according to the different substrates is compiled below :

    • Hydrocarbons: Friedel Crafts Alkylation and Acylation, Diel Alder reaction

    • Alkyl Halides: Wurtz Reaction, Fittig reaction, Wurtz Fittig reaction, Corey House synthesis, Finkelstein reaction, Swarts reaction

    • Alcohols, Phenols and Ethers: Riemer Tiemann reaction, Kolbe’s Reaction, Pinacol Pinacolone rearrangement

    • Carbonyl Compounds, Carboxylic Acid and Derivatives: Aldol Condensation, Cannizzaro Reaction, Etard Reaction, Clemmenson’s and Wolf Kishner reductions, Benzillic acid rearrangement, Benzoin Condensation, Beckmann’s rearrangement, Haloform reaction, Claisen condensation, Perkin condensation, Rosenmund reduction

    Reactions of Amines: Hoffman Bromamide degradation reaction, Curtius Rearrangement, Schmidt rearrangement, Gabriel Phthalimide synthesis, Sandmeyer reaction, Gatterman reaction

    Another significant set of Name Reactions include the tests for identification of different functional groups. The tests include Baeyer’s Reagent test, Lucas Reagent test, Victor Meyer’s test, Tollen’s test, Fehling’s test, Benedict’s Test, Hinsberg’s test, Carbylamine test, to name a few.

    These reactions are important as these are asked about directly in the exams and many of them are fairly straightforward. However some of these are also mechanism-based and it is these mechanisms that you should be particularly careful with while preparing for entrance exams. Identifying markers because of which the organic compounds respond to a particular test is a good way of learning them.

    Structure-Based Questions

    These questions mainly focus on the structures of organic compounds, like Polymers, Biomolecules, and the collection of different drugs in one of the Organic Chemistry chapters of Class 12 – “ Chemistry in Everyday Life”. These problems require some level of thorough learning as you have to memorise the structures of the compounds present. Each of these chapters has a different pattern of problems asked from them which may be directly or indirectly related to the structures.

    For example, problems related to Polymers usually involve identifying the monomers, their mode of polymerisation and also their uses. Problems from Biomolecules mostly deal with Carbohydrates, Amino Acids and Nucleic acids. Focus on the different sugars, their reducing nature, the type of glycosidic linkages and the different monosaccharides involved in formation of the polysaccharides. Remembering the structure of the different Amino Acids and Nucleic Acids is also important.

    A new pattern of problems from “Chemistry in Everyday Life” has been very recently introduced in the JEE Main examination and they appear to demand rote learning.. Solving these requires you to remember the structures of the different drugs, the functional groups present in them and the tests they would respond to, and the number of chiral centres present in the molecule. This was introduced in 2019 when the National Testing Agency (NTA) first conducted the JEE Main; problems of this type were present also in the 2020 sets. However, the number of these problems decreased significantly in the NTA JEE in the 2021 sets, to the relief of students. Despite that, these cannot be ignored as problems from previous years’ question papers are often repeated cyclically with slight modifications.

    • Chemistry
    • Physical sciences
    • Physical chemistry
    • Change
    • Chemical substances
    • Chemical reaction
    • Organic chemistry
    • Unit processes
    • chemical reactions

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