GATE Chemistry 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 GATE Chemistry, not a summary of it.

1. 1

   Stereochemistry

   6 topics

   • Chirality and Symmetry of Organic Molecules
     • Chiral centers
     • Absolute configurations
   • Relative Stereochemistry
     • Compounds with multiple stereogenic centers
     • Homotopic, enantiotopic, and diastereotopic atoms, groups, and faces
   • Stereoselective and Stereospecific Synthesis
   • Conformational Analysis
     • Acyclic compounds
     • Cyclic compounds
   • Isomerism
     • Geometrical isomerism
     • Optical isomerism
   • Configurational and Conformational Effects
     • Atropisomerism
     • Neighbouring group participation on reactivity and selectivity/specificity
2. 2

   Reaction Mechanisms

   8 topics

   • Basic Mechanistic Concepts
     • Kinetic versus thermodynamic control
     • Hammond’s postulate
     • Curtin-Hammett principle
   • Methods of Determining Reaction Mechanisms
     • Kinetics
     • Identification of products and intermediates
     • Isotopic labelling
   • Linear Free-Energy Relationship
     • Hammett and Taft equations
   • Nucleophilic and Electrophilic Substitution Reactions
     • Aromatic and aliphatic
   • Addition Reactions
     • To carbon-carbon and carbon-heteroatom (N and O) multiple bonds
   • Elimination Reactions
   • Reactive Intermediates
     • Carbocations
     • Carbanions
     • Carbenes
     • Nitrenes
     • Arynes
     • Free radicals
   • Molecular Rearrangements
3. 3

   Organic Synthesis

   8 topics

   • Synthesis, Reactions, Mechanisms, and Selectivity
     • Alkenes
     • Alkynes
     • Arenes
     • Alcohols
     • Phenols
     • Aldehydes
     • Ketones
     • Carboxylic acids
     • Esters
     • Nitriles
     • Halides
     • Nitro compounds
     • Amines
     • Amides
   • Uses of Reagents in Organic Synthesis
     • Mg
     • Li
     • Cu
     • B
     • Zn
     • P
     • S
     • Sn
     • Si
   • Carbon-Carbon Bond Formation
     • Coupling reactions
     • Concepts of multistep synthesis
   • Atom Economy and Green Chemistry
   • Umpolung Reactivity
     • Formyl and acyl anion equivalents
   • Selectivity in Organic Synthesis
     • Chemo-, regio-, and stereoselectivity
     • Protection and deprotection of functional groups
   • Asymmetric Synthesis
     • Resolution
     • Desymmetrization
     • Use of chiral auxiliaries
     • Organocatalysis
   • Carbon-Carbon and Carbon-Heteroatom Bond Forming Reactions
     • Enolates
     • Enamines
     • Silyl enol ethers
     • Stereoselective addition to C=O groups
4. 4

   Pericyclic Reactions and Photochemistry

   4 topics

   • Pericyclic Reactions
     • Electrocyclic, cycloaddition, and sigmatropic reactions
     • Orbital correlations
   • Photochemistry
     • Alkenes
     • Arenes
     • Carbonyl compounds
   • Photooxidation and Photoreduction
   • Other Reactions
     • Di-π-methane rearrangement
     • Barton-McCombie reaction
     • Norrish type-I and II cleavage reaction
5. 5

   Heterocyclic Compounds

   1 topic

   • Structure, Preparation, Properties, and Reactions
     • Furan
     • Pyrrole
     • Thiophene
     • Pyridine
     • Indole
     • Quinoline
     • Isoquinoline
6. 6

   Biomolecules

   1 topic

   • Structure, Properties, and Reactions
     • Mono- and di-saccharides
     • Amino acids
     • Peptides
     • Proteins
     • Nucleic acids
     • Lipids
     • Steroids
     • Terpenoids
     • Carotenoids
     • Alkaloids
7. 7

   Experimental Techniques in Organic Chemistry

   3 topics

   • Optical Rotation
     • Polarimetry
   • Chromatographic Techniques
     • Thin-layer
     • Column
     • HPLC
     • GC
   • Spectrometry
     • UV-visible
     • IR
     • NMR
     • Mass

Organic Chemistry flashcards for GATE Chemistry

25 of 51 cards from the Organic Chemistry deck — real questions with worked answers.

1. What is chirality in organic chemistry?

   Chirality is the geometric property of a molecule (or object) that is non-superimposable on its mirror image. A chiral molecule lacks an improper axis of symmetry ($S_n$), most commonly lacking a plane of symmetry ($\sigma$) and a center of inversion ($i$).

2. What symmetry element must a molecule lack to be chiral?

   A molecule is chiral if and only if it lacks any improper rotation axis $S_n$. Since $S_1 = \sigma$ (mirror plane) and $S_2 = i$ (center of inversion), absence of all $S_n$ guarantees chirality.

3. Define a stereogenic (chiral) center.

   A stereogenic (chiral) center is an atom, usually a tetrahedral $sp^3$ carbon, bearing four different substituents, such that interchanging any two substituents produces a different stereoisomer.

4. State the maximum number of stereoisomers for a molecule with $n$ stereogenic centers.

   The maximum number of stereoisomers is $2^{n}$. This maximum is reduced when meso forms or other internal symmetry make some configurations identical.

5. What are the CIP (Cahn–Ingold–Prelog) priority rules used for?

   CIP rules assign $R$/$S$ absolute configuration. Substituents are ranked by atomic number (higher = higher priority); ties are broken by exploring outward atom by atom, and duplicate atoms are used to represent double/triple bonds.

6. How do you assign $R$ vs $S$ configuration once priorities are set?

   Orient the lowest priority group (4) away from the viewer. If the sequence $1 \to 2 \to 3$ is clockwise the center is $R$ (rectus); if counterclockwise it is $S$ (sinister).

7. What is the difference between absolute and relative configuration?

   Absolute configuration specifies the actual 3D spatial arrangement at a stereocenter ($R$ or $S$). Relative configuration describes the spatial relationship between two or more stereocenters (e.g. cis/trans, syn/anti, threo/erythro) without fixing the absolute handedness.

8. Define enantiomers.

   Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They have identical scalar physical properties but rotate plane-polarized light in equal and opposite directions and differ in reactions with other chiral entities.

9. Define diastereomers.

   Diastereomers are stereoisomers that are not mirror images of each other. They have different physical properties (melting point, solubility, $\Delta H$, etc.) and arise when a molecule has multiple stereocenters with non-opposite configurations, or from cis/trans isomers.

10. What is a meso compound?

    A meso compound contains two or more stereogenic centers but is achiral overall due to an internal mirror plane (or other $S_n$). It is superimposable on its mirror image and is optically inactive despite having chiral centers, e.g. meso-tartaric acid.

11. Define homotopic atoms or groups.

    Homotopic groups are related by a proper rotation axis ($C_n$) so that interchanging them gives an identical (superimposable) molecule. They are chemically and spectroscopically equivalent in all environments, e.g. the two H atoms of $\ce{CH2Cl2}$ via $C_2$.

12. Define enantiotopic atoms or groups.

    Enantiotopic groups are related only by an improper symmetry element ($\sigma$, $i$, or $S_n$), not by any $C_n$. Replacing one vs the other gives enantiomers. They are equivalent in achiral environments but distinguishable in chiral ones (e.g. enzymes).

13. Define diastereotopic atoms or groups.

    Diastereotopic groups are not related by any symmetry operation. Replacing one vs the other gives diastereomers. They are inequivalent in all environments and generally show different NMR chemical shifts.

14. What is the substitution test for classifying topic relationships?

    Replace each of the two groups in turn by a test group and compare the products: identical $\Rightarrow$ homotopic; enantiomers $\Rightarrow$ enantiotopic; diastereomers $\Rightarrow$ diastereotopic; constitutional isomers $\Rightarrow$ constitutionally heterotopic.

15. Distinguish the Re and Si faces of a trigonal ($sp^2$) carbon.

    Looking at a face of a trigonal carbon, rank the three attached groups by CIP priority. If $1 \to 2 \to 3$ is clockwise it is the Re face; if counterclockwise it is the Si face. The two faces of a carbonyl are prochiral (often enantiotopic or diastereotopic).

16. Distinguish a stereoselective from a stereospecific reaction.

    A stereoselective reaction produces predominantly one stereoisomer from possible alternatives. A stereospecific reaction is one in which a particular stereoisomer of the starting material gives a particular stereoisomer of the product (mechanism-dictated, e.g. $S_N2$ inversion, anti addition of $\ce{Br2}$).

17. Is every stereospecific reaction stereoselective? Is the converse true?

    Every stereospecific reaction is necessarily stereoselective, but not every stereoselective reaction is stereospecific. Stereospecificity requires that different stereoisomeric reactants give different stereoisomeric products.

18. What does conformational analysis study?

    Conformational analysis studies the different spatial arrangements (conformers) that interconvert by rotation about single bonds, their relative energies, and how conformation influences reactivity, stability, and physical properties.

19. List the conformations of ethane in order of energy.

    Staggered (most stable, dihedral $60^{\circ}$) is lower in energy than eclipsed (least stable, dihedral $0^{\circ}$). The rotational barrier is about $12\ \text{kJ mol}^{-1}$ ($\approx 2.9\ \text{kcal mol}^{-1}$), arising mainly from hyperconjugation/torsional strain.

20. Name the four key conformations of n-butane about the C2–C3 bond.

    In order of increasing energy: anti (dihedral $180^{\circ}$, most stable) < gauche (dihedral $60^{\circ}$) < eclipsed (dihedral $120^{\circ}$) < fully eclipsed / syn (dihedral $0^{\circ}$, highest, methyl–methyl eclipsing).

21. What is gauche strain?

    Gauche strain (a form of steric/van der Waals strain) is the repulsion between two bulky groups held at a $60^{\circ}$ dihedral angle in a gauche conformation, raising its energy relative to the anti conformer by about $3.8\ \text{kJ mol}^{-1}$ for butane.

22. Which conformation of cyclohexane is most stable and why?

    The chair conformation is most stable because all bonds are perfectly staggered (no torsional strain) and bond angles are near the ideal tetrahedral $109.5^{\circ}$, minimizing angle strain. Twist-boat and boat are higher in energy.

23. Compare axial vs equatorial substituents on cyclohexane.

    Equatorial substituents are sterically favored because axial substituents suffer 1,3-diaxial interactions. At equilibrium the conformer with the larger group equatorial predominates; e.g. methylcyclohexane is ~95% equatorial.

24. What is the A-value of a substituent?

    The A-value is the conformational free-energy preference for a substituent to occupy the equatorial position on cyclohexane, defined as $A = -\Delta G^{\circ} = -RT\ln K$ for the axial$\rightleftharpoons$equatorial equilibrium. Larger A-value means stronger equatorial preference (e.g. $t$-Bu $\approx 4.9\ \text{kcal mol}^{-1}$).

25. What causes ring strain in cyclopropane?

    Cyclopropane has severe angle strain (internal angle $60^{\circ}$ vs ideal $109.5^{\circ}$) plus torsional strain from fully eclipsed C–H bonds, giving bent ('banana') bonds and a total ring strain of about $115\ \text{kJ mol}^{-1}$.

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