CSIR NET Chemical Sciences Organic Chemistry Syllabus

Organic Chemistry syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Organic Chemistry in CSIR NET Chemical Sciences, not a summary of it.

1. 1

   Stereochemistry

   3 topics

   • Concepts of Chirality
   • Optical Activity
   • Stereoisomerism
2. 2

   Reaction Mechanisms

   3 topics

   • Nucleophilic Substitution Reactions
   • Electrophilic Addition Reactions
   • Free Radical Mechanisms
3. 3

   Organic Synthesis

   3 topics

   • Reagents in Organic Synthesis
   • Strategies for Organic Synthesis
   • Protecting Groups
4. 4

   Pericyclic Reactions

   3 topics

   • Cycloaddition Reactions
   • Sigmatropic Rearrangements
   • Electrocyclic Reactions
5. 5

   Heterocyclic Compounds

   2 topics

   • Properties and Reactions of Common Heterocycles
   • Synthesis of Heterocycles
6. 6

   Biomolecules

   4 topics

   • Carbohydrates
   • Proteins
   • Nucleic Acids
   • Lipids
7. 7

   Spectroscopy

   4 topics

   • Principles of UV-Visible Spectroscopy
   • IR Spectroscopy
   • NMR Spectroscopy
   • Mass Spectrometry

Organic Chemistry flashcards for CSIR NET Chemical Sciences

25 of 55 cards from the Organic Chemistry deck — real questions with worked answers.

1. What is chirality, and what is the defining feature of a chiral molecule?

   Chirality is the geometric property of a molecule being non-superimposable on its mirror image. The defining feature is the absence of an improper axis of symmetry (Sn), most commonly meaning no plane of symmetry and no center of symmetry.

2. Distinguish between enantiomers and diastereomers.

   Enantiomers are stereoisomers that are non-superimposable mirror images and have identical physical properties except optical rotation direction. Diastereomers are stereoisomers that are NOT mirror images; they have different physical properties (mp, bp, solubility).

3. State the R/S (CIP) priority rule for assigning configuration at a stereocenter.

   Rank the four groups by atomic number (higher = higher priority); with lowest priority pointing away, if 1->2->3 traces clockwise it is R (rectus), counterclockwise it is S (sinister). Ties are broken by comparing the next atoms outward.

4. What is a meso compound?

   A meso compound contains stereocenters but is achiral overall because it possesses an internal plane (or center) of symmetry, making it superimposable on its mirror image (optically inactive despite having chiral centers).

5. Define optical activity and give the equation for specific rotation.

   Optical activity is the ability of a chiral substance to rotate the plane of plane-polarized light. Specific rotation [alpha] = alpha_observed / (l x c), where l is path length in dm and c is concentration in g/mL.

6. What is a racemic mixture and what is its net optical rotation?

   A racemic mixture (racemate) is a 1:1 mixture of two enantiomers. Its net optical rotation is zero because the rotations of the two enantiomers cancel exactly.

7. How is enantiomeric excess (ee) calculated?

   ee (%) = (|[R] - [S]| / ([R] + [S])) x 100, equivalently the % of the major enantiomer minus the % of the minor enantiomer. It can also equal (observed rotation / rotation of pure enantiomer) x 100.

8. What is atropisomerism?

   Atropisomerism is a form of conformational chirality arising from restricted rotation about a single bond (e.g., ortho-substituted biphenyls), giving isolable stereoisomers that are configurationally stable at the relevant temperature.

9. Compare the mechanisms and stereochemistry of SN1 and SN2 reactions.

   SN1: two steps via a carbocation, first-order kinetics, racemization, favored by tertiary substrates and polar protic solvents. SN2: one concerted step, second-order kinetics, backside attack with inversion (Walden inversion), favored by primary substrates and polar aprotic solvents.

10. List the order of substrate reactivity for SN1 and for SN2 reactions.

    SN1: tertiary > secondary > primary > methyl (carbocation stability). SN2: methyl > primary > secondary > tertiary (steric accessibility).

11. What is the order of nucleophilicity of halides in protic vs aprotic solvents?

    In polar protic solvents: I- > Br- > Cl- > F- (large ions less solvated). In polar aprotic solvents the trend reverses toward basicity: F- > Cl- > Br- > I-.

12. State Markovnikov's rule for electrophilic addition to alkenes.

    In addition of HX to an unsymmetrical alkene, the hydrogen adds to the carbon with more hydrogens and the halogen (electrophile's other part) to the more substituted carbon, because the more stable (more substituted) carbocation forms preferentially.

13. What is anti-Markovnikov addition and what conditions produce it?

    Anti-Markovnikov addition places H on the more substituted carbon. It occurs with HBr in the presence of peroxides (radical mechanism, the peroxide effect) and in hydroboration-oxidation, where boron adds to the less hindered carbon.

14. What is the stereochemistry of bromine (Br2) addition to alkenes and why?

    Anti addition (trans), because the reaction proceeds through a cyclic bromonium ion intermediate that is opened by backside attack of bromide on the opposite face.

15. Describe the three steps of a free radical chain mechanism.

    Initiation: homolytic bond cleavage generating radicals (e.g., by heat or light). Propagation: radicals react to form product and regenerate radicals. Termination: two radicals combine, ending the chain.

16. What is the order of free radical stability and how does it relate to selectivity?

    Radical stability: tertiary > secondary > primary > methyl (hyperconjugation and induction). More stable radicals form preferentially; bromination is more selective than chlorination because Br abstraction is endothermic (later, more product-like transition state).

17. What does LiAlH4 reduce versus NaBH4?

    LiAlH4 is a strong reducing agent: reduces aldehydes, ketones, carboxylic acids, esters, amides, nitriles, and epoxides. NaBH4 is milder: reduces aldehydes and ketones (and acid chlorides) but generally not esters, acids, or amides.

18. What transformations do (a) PCC and (b) KMnO4 (hot, conc.) perform on alcohols?

    (a) PCC oxidizes primary alcohols to aldehydes and secondary alcohols to ketones without over-oxidation (mild, anhydrous). (b) Hot concentrated KMnO4 oxidizes primary alcohols all the way to carboxylic acids and secondary to ketones.

19. What reagent and conditions accomplish ozonolysis, and what does reductive workup give?

    O3 cleaves C=C double bonds to form an ozonide; reductive workup (Zn/AcOH or Me2S/dimethyl sulfide) gives aldehydes and/or ketones, while oxidative workup (H2O2) gives carboxylic acids/ketones.

20. In retrosynthetic analysis, define 'disconnection' and 'synthon'.

    A disconnection is the conceptual breaking of a bond to convert a target molecule into simpler precursors. A synthon is an idealized fragment (often a cation or anion) resulting from disconnection; the real reagent corresponding to a synthon is its 'synthetic equivalent'.

21. What is umpolung (polarity reversal) in synthesis? Give a classic example.

    Umpolung is the reversal of the normal electronic character of a functional group. The classic example is converting an aldehyde (electrophilic carbonyl carbon) into a nucleophilic acyl anion equivalent via a dithiane (1,3-dithiane formation, then deprotonation).

22. What is a convergent synthesis and why is it preferred over a linear synthesis?

    A convergent synthesis builds large fragments separately and joins them near the end, whereas a linear synthesis adds one step at a time. Convergent routes give higher overall yield and efficiency because losses are not multiplied across every step of the whole sequence.

23. Name a common protecting group for alcohols and how it is installed/removed.

    TBS (tert-butyldimethylsilyl) ether: installed with TBSCl/imidazole, removed with fluoride (TBAF). Other examples: acetate (Ac2O; removed by base hydrolysis) and benzyl ether (BnBr/base; removed by H2/Pd hydrogenolysis).

24. How are aldehydes/ketones and 1,2-diols protected?

    Carbonyls are protected as acetals/ketals (e.g., reaction with ethylene glycol/acid to give a 1,3-dioxolane), removed by aqueous acid. 1,2-diols are protected as acetonides (cyclic ketals with acetone), also removed by aqueous acid.

25. What protecting groups are commonly used for amines in peptide synthesis, and how are they removed?

    Boc (tert-butoxycarbonyl): removed by TFA (acid). Fmoc (9-fluorenylmethoxycarbonyl): removed by base (piperidine). Cbz/Z (benzyloxycarbonyl): removed by H2/Pd hydrogenolysis.

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