CSIR UGC NET Dec 2023 | CSIR Chemical Sciences | CSIR NET Detailed Solutions

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The #Chugaev reaction is a chemical reaction that involves the conversion of alcohols into alkenes through the formation of alkyl thiocarbonates followed by a rearrangement. This reaction is useful for the dehydrolysis of alcohols, providing a method for alkene synthesis. Mechanism Overview Formation of Alkyl Thiocarbonate: The reaction begins with the treatment of an alcohol with a thiophosgene (or a thioketone), resulting in the formation of an alkyl thiocarbonate. The thiophosgene acts as a reagent that reacts with the hydroxyl group of the alcohol. R-OH + ClC(=S)R’ → R-O-C(=S)R’ + HCl R-OH+ClC(=S)R’→R-O-C(=S)R’+HCl Deprotonation: The alkyl thiocarbonate can then undergo deprotonation, often in the presence of a base, which makes the thiocarbonate more nucleophilic. Elimination to Form Alkene: Under suitable conditions (often heat), the alkyl thiocarbonate undergoes elimination, resulting in the formation of an alkene. This step involves the loss of the thiocarbonate group, leading to the formation of a double bond. R-O-C(=S)R’ → R=R’ + CO + S R-O-C(=S)R’→R=R’+CO+S Key Features Substrate Scope: The reaction can be applied to various primary and secondary alcohols. Regioselectivity: The reaction can provide a certain degree of control over the regioselectivity of the alkene formed, depending on the reaction conditions. Temperature Dependence: The reaction typically requires heating to facilitate the elimination step. Applications The Chugaev reaction is used in synthetic organic chemistry to prepare alkenes, which are valuable intermediates in the synthesis of various organic compounds, including pharmaceuticals and fine chemicals.

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👉 CSIR UGC NET - 2023 December 27th - Chemistry - kzbin.info/www/bejne/rX-am3pso9irf7M PDF Download with solutions: drive.google.com/file/d/18vFz-T8gSCYjEjOjH2tVrcqp8VNYTLqx/view?usp=sharing 👉 CSIR UGC NET - 2023 June 7th - Chemistry - kzbin.info/www/bejne/i5vdfWiOaJeYqKs PDF Download with solutions: drive.google.com/file/d/1LRok2-oHilvzkV0fg2KVaMCl1haURK5t/view 👉 CSIR UGC NET - 2022 Feb 16th - Chemistry kzbin.info/www/bejne/ipOqmaiggtuKp9U PDF Download with solutions: drive.google.com/file/d/1_d68vw2mGVHwRAPQfecKXxKsBOB8DBCt/view 👉 CSIR UGC NET - 2019 December 15th - Chemistry docs.google.com/forms/d/e/1FAIpQLSdFea-H7pS9bO129_5CUeD_wd0kNg5m09otvYOSAW1d5dsXVw/viewform PDF Download with solutions: drive.google.com/file/d/1WRwk2C8xdu1CkjS2dADiIOBWK2xFfurt/view

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#VSEPR theory, or Valence Shell Electron Pair Repulsion theory, is a model used to predict the geometry of molecules based on the repulsion between electron pairs surrounding a central atom. Here’s an overview of the key concepts: Key Principles of VSEPR Theory Electron Pair Repulsion: Electron pairs (both bonding pairs and lone pairs) repel each other because they are negatively charged. The arrangement of these pairs around a central atom determines the molecular shape. Types of Electron Pairs: Bonding pairs: Electrons shared between two atoms. Lone pairs: Electrons that are not involved in bonding and belong to a single atom. Geometry Based on Electron Pairs: The spatial arrangement of the electron pairs minimizes repulsion, leading to specific molecular shapes. Different arrangements correspond to different numbers of electron pairs. Common Molecular Geometries Linear: Electron pairs: 2 Bond angle: 180° Example: BeCl₂ Trigonal Planar: Electron pairs: 3 Bond angle: 120° Example: BF₃ Tetrahedral: Electron pairs: 4 Bond angle: 109.5° Example: CH₄ Trigonal Bipyramidal: Electron pairs: 5 Bond angles: 90° and 120° Example: PCl₅ Octahedral: Electron pairs: 6 Bond angle: 90° Example: SF₆ Adjustments for Lone Pairs Lone pairs occupy more space than bonding pairs, causing greater repulsion and affecting the bond angles. For example: In a tetrahedral arrangement with one lone pair (e.g., NH₃), the geometry becomes trigonal pyramidal with bond angles slightly less than 109.5°. With two lone pairs (e.g., H₂O), the geometry is bent with bond angles around 104.5°. Summary VSEPR theory provides a simple way to predict the shapes of molecules based on the number and types of electron pairs around a central atom. This theory is foundational in understanding molecular geometry, which is critical for predicting reactivity and properties of molecules.

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The #Birch #reduction is a well-known organic reaction that involves the reduction of aromatic compounds to form non-conjugated cyclohexadienes. This reaction typically uses sodium (Na) or lithium (Li) in liquid ammonia (NH₃) along with an alcohol (like ethanol or tert-butanol) as a proton source. Mechanism Overview Formation of the Radical Anion: The aromatic compound reacts with sodium in liquid ammonia, generating a radical anion. This step involves the transfer of an electron from the sodium to the aromatic ring, forming a resonance-stabilized radical anion. Ar-H + Na → Ar • + Na + + NH 3 Ar-H+Na→Ar • +Na + +NH 3 ​ Protonation: The radical anion can pick up a proton (H⁺) from the solvent or an alcohol, leading to the formation of a cyclohexadiene. Ar • + NH 3 → Ar-H + e − Ar • +NH 3 ​ →Ar-H+e − The protonation typically occurs at one of the positions of the radical anion. Formation of the Alkoxide Ion: After protonation, the resulting species can further react with another equivalent of sodium, creating an alkoxide ion (RO⁻). Ar-H + Na + ROH → Ar-OR + Na + + e − Ar-H+Na+ROH→Ar-OR+Na + +e − Second Protonation: The alkoxide can be protonated again, yielding the final cyclohexadiene product. Ar-OR + NH 3 → Ar-CH + ROH Ar-OR+NH 3 ​ →Ar-CH+ROH Key Points Substituent Effects: The reaction is affected by substituents on the aromatic ring. Electron-withdrawing groups favor the reaction, while electron-donating groups can slow it down. Selectivity: The Birch reduction typically leads to the formation of 1,4-cyclohexadienes, which are non-conjugated and stable. Conditions: Liquid ammonia serves as both solvent and a source of protons, with the reaction often performed at low temperatures. Summary The Birch reduction is an important synthetic method in organic chemistry for converting aromatic compounds into partially reduced products. Its ability to selectively reduce certain substrates while leaving others intact makes it valuable in complex molecule synthesis.

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The Michael addition is a nucleophilic addition reaction in which a nucleophile attacks a conjugated system (usually an α,β-unsaturated carbonyl compound) to form a new carbon-carbon bond. This reaction is widely used in organic synthesis to create complex molecules. Mechanism Overview Nucleophilic Attack: The reaction begins with a nucleophile (often an enolate ion or a stabilized nucleophile) attacking the β-carbon of the α,β-unsaturated carbonyl compound. This carbon is electrophilic due to the electron-withdrawing effect of the carbonyl group. The nucleophile donates a pair of electrons to form a new bond, resulting in a tetrahedral intermediate. Nucleophile + C=C → Tetrahedral Intermediate Nucleophile+C=C→Tetrahedral Intermediate Tetrahedral Intermediate Formation: The nucleophile adds to the β-carbon, creating a tetrahedral intermediate. The carbonyl group’s double bond is temporarily broken, and a negative charge develops on the oxygen. Proton Transfer: The negatively charged oxygen can either be protonated by a solvent or by an acid to stabilize the intermediate. Elimination: The tetrahedral intermediate then collapses, leading to the reformation of the carbonyl group. In this step, the leaving group (usually a hydroxyl group formed from the original carbonyl) is expelled, resulting in a β-keto or β-hydroxy carbonyl compound. Tetrahedral Intermediate → α,β-Unsaturated Carbonyl Compound Tetrahedral Intermediate→α,β-Unsaturated Carbonyl Compound Example For example, when an enolate ion (from a ketone) attacks methyl acrylate: The enolate attacks the β-carbon of methyl acrylate. The tetrahedral intermediate is formed. Proton transfer occurs, stabilizing the intermediate. Elimination results in a new product, like a β-keto ester. Key Features Nucleophiles: Common nucleophiles include enolates, alcohols, amines, or other stabilized nucleophiles. Reaction Conditions: The reaction can be catalyzed by bases or acids depending on the nucleophile used. Selectivity: The reaction's regioselectivity is determined by the nucleophile and the specific structure of the α,β-unsaturated compound. Applications The Michael addition is widely used in the synthesis of pharmaceuticals, natural products, and complex organic compounds due to its ability to form C-C bonds selectively.

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The #Stille #coupling reaction is a powerful method in organic synthesis used to form carbon-carbon bonds. It involves the coupling of organostannanes (tin-containing compounds) with organic halides (typically bromides or iodides) in the presence of a palladium catalyst. Mechanism Overview Oxidative Addition: The first step involves the oxidative addition of the organic halide to the palladium(0) catalyst. The palladium adds to the carbon-halogen bond, resulting in the formation of a palladium(II) complex and the release of a halide ion. R-X + Pd(0) → R-Pd(II)-X R-X+Pd(0)→R-Pd(II)-X Transmetalation: In this step, the organostannane (R'Sn) reacts with the palladium(II) complex. The tin group transfers to the palladium, displacing the halide and forming a new palladium(II) complex with a new carbon-carbon bond. R-Pd(II)-X + R’Sn → R-R’Pd(II) + R’SnX R-Pd(II)-X+R’Sn→R-R’Pd(II)+R’SnX Reductive Elimination: The final step is reductive elimination, where the palladium(II) complex loses the palladium center, forming the desired coupled product (R-R') and regenerating the palladium(0) catalyst. R-R’Pd(II) → R-R’ + Pd(0) R-R’Pd(II)→R-R’+Pd(0) Summary of Steps Oxidative Addition: Formation of a palladium(II) halide complex. Transmetalation: Transfer of the organic group from the organostannane to the palladium. Reductive Elimination: Formation of the product and regeneration of the palladium catalyst. Key Features Catalyst: Typically, palladium(0) or palladium(II) complexes are used as catalysts. Substrate Scope: The reaction is highly versatile, allowing for the coupling of various organostannanes with a range of organic halides. Advantages: The Stille reaction is valued for its ability to form complex organic structures and for the mild conditions under which it can be carried out. This mechanism illustrates the fundamental steps in the Stille coupling reaction. If you have any specific questions or need further details, feel free to ask!

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The #Pinnick #oxidation is a chemical reaction used to convert alcohols into aldehydes or ketones using a combination of sodium chlorite (NaClO₂) and a suitable acid, typically acetic acid. This reaction is particularly useful in organic synthesis for the selective oxidation of primary and secondary alcohols. Mechanism Overview Activation of Sodium Chlorite: In the presence of an acid, sodium chlorite is protonated, which enhances its electrophilic character. Formation of Chlorite Ester: The protonated chlorite reacts with the alcohol to form a chlorite ester intermediate. Nucleophilic Attack: The chlorite ester undergoes nucleophilic attack by the alcohol's hydroxyl group. This leads to the formation of a tetrahedral intermediate. Elimination: The tetrahedral intermediate collapses, resulting in the formation of the carbonyl compound (aldehyde or ketone) and the release of chlorinated species. Rearrangement: The byproducts, including chlorinated water-soluble compounds, can be removed, leaving the desired carbonyl compound. Key Points Selectivity: The Pinnick oxidation is selective for primary and secondary alcohols, allowing for controlled oxidation. Conditions: Mild reaction conditions make it suitable for sensitive substrates. Byproducts: The reaction generates less toxic byproducts compared to other oxidation methods. Applications The Pinnick oxidation is valuable in synthetic organic chemistry for the preparation of aldehydes and ketones, which are important intermediates in various chemical processes.

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CSIR NET😂

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#Sharpless dihydroxylation is a stereoselective method for the syn-dihydroxylation of alkenes using osmium tetroxide (OsO₄) in the presence of a chiral ligand. This reaction is widely used in organic synthesis to produce vicinal diols with high stereoselectivity. Mechanism Overview Formation of the Osmium Complex: The reaction begins with the coordination of osmium tetroxide (OsO₄) to the alkene, forming a cyclic osmate ester. The alkene acts as a nucleophile, attacking one of the Os=O bonds. RCH=CHR + OsO 4 → [RCH(Os)R](cyclic osmate ester) RCH=CHR+OsO 4 ​ →[RCH(Os)R](cyclic osmate ester) Stereospecific Syn-Dihydroxylation: The cyclic osmate ester is a five-membered ring that contains an osmium atom bonded to two carbon atoms of the alkene. The geometry of this intermediate allows for the subsequent addition of hydroxyl groups (from water or an alcohol). The attack of the hydroxide ion occurs at the same face of the alkene, leading to syn addition, which means both hydroxyl groups are added to the same side of the double bond. Formation of the Dihydroxylated Product: The cyclic osmate ester can be hydrolyzed (or treated with a reagent like an alcohol) to yield the vicinal diol. During this step, the osmate ester is converted to an alcohol, regenerating the osmium tetroxide in the process. [RCH(Os)R] + H 2 𝑂 → RCH(OH)R + OsO 4 [RCH(Os)R]+H 2 ​ O→RCH(OH)R+OsO 4 ​ Recovery of Osmium: The osmium tetroxide can be recovered and reused in subsequent reactions, often with the assistance of a reducing agent to regenerate OsO₄. Key Points Chiral Ligands: The selectivity of the reaction can be enhanced using chiral ligands, such as (−)-diethyl tartrate (DET), which leads to the formation of enantiomerically enriched products. Stereochemical Outcome: The reaction produces syn-dihydroxylated products, meaning that both hydroxyl groups are added to the same face of the double bond. Environmental Considerations: Osmium tetroxide is toxic, so proper safety precautions should be taken during its use. Applications Sharpless dihydroxylation is particularly valuable in the synthesis of complex natural products and pharmaceuticals, where the selective formation of diols is often critical for biological activity.

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#Ozonolysis is a chemical reaction involving the cleavage of alkenes or alkynes using ozone (O₃), leading to the formation of carbonyl compounds (aldehydes, ketones, or carboxylic acids). It is a valuable reaction in organic chemistry for transforming unsaturated compounds into more functionalized products. Mechanism Overview The ozonolysis reaction generally proceeds in two main stages: the formation of a molozonide and its subsequent rearrangement to yield carbonyl compounds. 1. Formation of Molozonide The alkene (or alkyne) reacts with ozone to form a cyclic intermediate known as molozonide. The alkene attacks an ozone molecule, forming a primary ozonide (molozonide) as the initial product. RCH=CHR + O3 → [Molozonide] RCH=CHR+O 3​ →[Molozonide] 2. Rearrangement to Ozonide The molozonide is unstable and quickly rearranges to form a more stable ozonide. This involves the breaking of the O-O bond in the molozonide and the formation of a new carbon-oxygen bond. [Molozonide] → [Ozonide] [Molozonide]→[Ozonide] 3. Cleavage of Ozonide The ozonide can then undergo cleavage in the presence of a reducing agent, such as zinc (Zn) or dimethyl sulfide (DMS), or hydrolysis with water. This leads to the formation of carbonyl compounds: If the ozonide is reduced, the products will be aldehydes or ketones. If hydrolyzed, it can yield carboxylic acids. [Ozonide] → H 2 O RCHO + R’COOH [Ozonide] H 2 ​ O ​ RCHO+R’COOH Summary of Products With Aldehydes and Ketones: The ozonolysis of internal alkenes typically produces ketones. With Terminal Alkenes: Terminal alkenes typically produce an aldehyde and a ketone. With Alkynes: Alkynes can yield carboxylic acids upon ozonolysis. Key Features Selectivity: Ozonolysis is highly selective for alkenes and alkynes and allows for the generation of specific functional groups. Mild Conditions: The reaction occurs under mild conditions, making it compatible with a wide variety of functional groups. Safety Considerations: Ozone is a toxic gas, so proper safety precautions should be taken when performing ozonolysis. Ozonolysis is a valuable method in organic synthesis for introducing carbonyl functionalities, often used in the synthesis of complex molecules. If you have further questions or need specific examples, feel free to ask!

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Preparing for the CSIR UGC NET JRF can be challenging but rewarding. Here are some effective tips to help you prepare: 1. Understand the Syllabus and Exam Pattern Familiarize yourself with the syllabus for your subject. Understand the exam pattern, including the number of papers, types of questions, and marking scheme. 2. Create a Study Plan Develop a structured study schedule that covers all topics. Allocate more time to challenging subjects while ensuring all areas are addressed. 3. Use Quality Study Materials Refer to standard textbooks, research papers, and study guides. Utilize online resources, video lectures, and previous year question papers. 4. Practice Regularly Solve previous years’ question papers and sample papers. Take mock tests to improve time management and identify weak areas. 5. Focus on Conceptual Clarity Ensure you understand the core concepts rather than just memorizing facts. Discuss topics with peers or mentors to enhance understanding. 6. Revise Frequently Regular revision is crucial to retain information. Summarize key points, formulas, and concepts in a concise manner. 7. Stay Updated with Current Research Read research articles and stay updated on recent developments in your field. Follow relevant journals and academic publications. 8. Join Study Groups or Coaching Consider joining a study group or coaching institute for guidance and motivation. Engaging with others can provide different perspectives and resources. 9. Manage Your Health Ensure you’re physically and mentally fit; take breaks and practice relaxation techniques. Maintain a balanced diet and get adequate sleep. 10. Stay Positive and Persistent Keep a positive attitude throughout your preparation. Stay motivated and focused on your goal, even if you face challenges. 11. Prepare for the Interview (if applicable) If you qualify for JRF, prepare for the interview process by reviewing your research interests and academic background. 12. Seek Guidance When Needed Don’t hesitate to ask for help from teachers or mentors if you’re struggling with specific topics. By following these tips and maintaining a dedicated approach, you can enhance your preparation for the CSIR UGC NET JRF exam. Good luck!