Organic Chemistry: Some Basic Principles and Techniques (GOC) Revision Notes

 Short Q&A for Reaction Mechanism in Organic Chemistry (Class 11 NCERT)

Part 1: Bond Fission and Reactive Intermediates

Q. No.	Question	Answer
1	What is Homolytic Fission?	The bond cleavage where each bonded atom takes one electron of the shared pair.
2	What is the electronic species formed during homolytic fission?	Free Radical (R⋅).
3	What is Heterolytic Fission?	The bond cleavage where the shared electron pair stays with one of the fragments.
4	What are the two types of charged species formed during heterolytic fission?	Carbocation (R+) and Carbanion (R−).
5	What conditions favor homolytic fission?	High temperature, light (UV), non-polar solvents, or the presence of peroxides.
6	What conditions favor heterolytic fission?	Polar solvents (e.g., water) and a significant electronegativity difference in the bond.
7	Define a Carbocation.	A species containing a carbon atom with a positive charge and only six valence electrons (electron deficient).
8	Define a Carbanion.	A species containing a carbon atom with a negative charge and a full octet (eight valence electrons).
9	Define a Free Radical.	A neutral species containing a carbon atom with an unpaired electron.
10	What is the geometry and hybridization of a simple Carbocation (CH3+​)?	Trigonal Planar, sp2 hybridization.
11	What is the geometry and hybridization of a simple Carbanion (CH3−​)?	Pyramidal, sp3 hybridization.
12	What is the geometry and hybridization of a simple Alkyl Free Radical (CH3​⋅)?	Planar or slightly Pyramidal, usually sp2 or sp3.
13	Rank the stability of alkyl carbocations (1∘,2∘,3∘).	3∘>2∘>1∘.
14	Rank the stability of alkyl free radicals (1∘,2∘,3∘).	3∘>2∘>1∘.
15	Rank the stability of alkyl carbanions (1∘,2∘,3∘).	1∘>2∘>3∘ (opposite to carbocations/radicals).
16	What electronic effects stabilize Carbocations?	Inductive Effect (+I) and Hyperconjugation.
17	What electronic effects stabilize Carbanions?	Inductive Effect (–I) and Resonance/Mesomeric Effect (–M).
18	Which is generally the most stable reactive intermediate?	A species stabilized by Resonance (e.g., Benzyl or Allyl carbocation/radical).
19	What is the general name for the species that forms the new bond by attacking the substrate?	Attacking Reagent.

Part 2: Attacking Reagents (Electrophiles and Nucleophiles)

Q. No.	Question	Answer
20	Define an Electrophile.	An electron-deficient species (electron-loving, acts as a Lewis Acid).
21	Give two examples of positively charged Electrophiles.	H+,NO2+​,CH3+​ (Carbocation).
22	Give two examples of neutral Electrophiles.	AlCl3​,BF3​,SO3​ (Lewis Acids with incomplete octet).
23	Define a Nucleophile.	An electron-rich species (nucleus-loving, acts as a Lewis Base).
24	Give two examples of negatively charged Nucleophiles.	OH−,CN−,R3​C− (Carbanion).
25	Give two examples of neutral Nucleophiles.	H2​O,NH3​,R-OH (species with lone pairs).
26	Where do Electrophiles typically attack the substrate molecule?	At the site of high electron density (e.g., π-bond or negative charge).
27	Where do Nucleophiles typically attack the substrate molecule?	At the site of low electron density (e.g., C atom of C=O or C+).
28	How is Nucleophilicity related to Basicity?	They are similar but not identical; nucleophilicity is a kinetic concept (rate of attack), basicity is a thermodynamic concept (equilibrium of proton acceptance).
29	Which is a stronger nucleophile in polar protic solvents: F− or I−?	I− (F− is strongly solvated, reducing its nucleophilicity).
30	Which is a stronger base: F− or I−?	F− (based on pKa​ of conjugate acid HF).

Part 3: Electronic Effects (Permanent Effects)

Q. No.	Question	Answer
31	What is the Inductive Effect (I-effect)?	The polarization of σ-bonds caused by the unequal sharing of electrons due to a difference in electronegativity.
32	Is the Inductive Effect a temporary or permanent effect?	Permanent effect.
33	How does the magnitude of the Inductive Effect change with distance?	It decreases rapidly with distance and becomes negligible after 3-4 carbon atoms.
34	Define the +I Effect (Positive Inductive Effect).	The electron-releasing or electron-donating tendency of a group (e.g., alkyl groups).
35	Define the −I Effect (Negative Inductive Effect).	The electron-withdrawing tendency of a group (e.g., NO2​,CN).
36	Give the order of stability for Carboxylic Acids (Acidity) based on the −I effect.	−I group increases acidity by stabilizing the conjugate base.
37	What is the Resonance Effect (M-effect) or Mesomeric Effect?	The delocalization of π-electrons (or lone pairs) within a conjugated system.
38	Is the Resonance Effect a temporary or permanent effect?	Permanent effect.
39	Define the +M Effect (Positive Mesomeric Effect).	The group releases electrons into the conjugated system (e.g., OH,NH2​).
40	Define the −M Effect (Negative Mesomeric Effect).	The group withdraws electrons from the conjugated system (e.g., NO2​,CHO).
41	What are Canonical Forms (or Resonating Structures)?	Hypothetical structures used to represent the true structure (resonance hybrid) of a molecule with delocalized electrons.
42	Which is more stable: a resonance hybrid or its canonical forms?	The Resonance Hybrid (due to resonance energy).
43	What is the condition necessary for a molecule to show resonance?	It must have a conjugated system (π-bonds alternating with single bonds or lone pairs).
44	Which effect stabilizes the negative charge on the carboxylate ion (RCOO−)?	Resonance (two equivalent resonating structures).
45	What is Hyperconjugation (or the No-Bond Resonance/Baker-Nathan Effect)?	The delocalization of σ-electrons of a C-H bond of an alkyl group adjacent to an unsaturated system.
46	What electronic species does Hyperconjugation involve?	σ electrons (specifically C-H bond electrons).
47	How many α-hydrogens are in the tert-butyl carbocation?	Nine α-hydrogens (three CH3​ groups ×3H).
48	How does the number of α-hydrogens relate to stability?	More α-hydrogens means greater stability (due to more hyperconjugative structures).
49	Rank the stabilizing effects in terms of magnitude (excluding E-effect).	Resonance (M) > Hyperconjugation (H) > Inductive (I).

Part 4: Electronic Effects (Temporary Effect) and Reaction Types

Q. No.	Question	Answer
50	What is the Electromeric Effect (E-effect)?	The complete transfer of π-electrons of a multiple bond to one of the bonded atoms in the presence of an attacking reagent.
51	Is the Electromeric Effect a temporary or permanent effect?	Temporary effect (only active when the reagent is present).
52	Define the +E Effect (Positive Electromeric Effect).	The π-electrons are transferred towards the atom to which the attacking reagent gets attached (e.g., addition of H+ to C=C).
53	Define the −E Effect (Negative Electromeric Effect).	The π-electrons are transferred away from the atom to which the attacking reagent gets attached (e.g., attack of CN− on C=O).
54	What is the main characteristic difference between the I-effect and the E-effect?	I-effect involves σ-electrons (partial shift); E-effect involves π-electrons (complete transfer).
55	What are the four major types of organic reactions?	Substitution, Addition, Elimination, and Rearrangement.
56	Define an Addition Reaction.	Two molecules combine to form a single product (characteristic of unsaturated compounds).
57	Define a Substitution Reaction.	An atom or group of atoms in a molecule is replaced by another atom or group.
58	Define an Elimination Reaction.	Two atoms or groups are removed from a molecule, resulting in the formation of a multiple bond.
59	What type of reagents typically initiate reactions in Alkanes (e.g., halogenation)?	Free Radicals (Free Radical Substitution).
60	What type of reagents typically initiate reactions in Alkenes (C=C)?	Electrophiles (Electrophilic Addition).
61	What type of reagents typically initiate reactions in Alkyl Halides?	Nucleophiles (Nucleophilic Substitution).
62	What is Saytzeff's Rule (or Zaitsev's Rule)?	In elimination reactions, the more substituted (more stable) alkene product is the major product.
63	What is Markownikoff's Rule?	In the addition of HX to an unsymmetrical alkene, the negative part (X) goes to the carbon atom with fewer hydrogen atoms.
64	What mechanism is associated with Markownikoff's Rule?	Electrophilic Addition (involving carbocation intermediate).
65	What is the Anti-Markownikoff's Rule (or Peroxide Effect)?	Addition of HBr (only) to an unsymmetrical alkene in the presence of peroxides occurs via a free radical mechanism.

Part 5: Stereochemistry and Reaction Mechanism

Q. No.	Question	Answer
66	What is Chirality?	The property of an object (or molecule) being non-superimposable on its mirror image.
67	What is the most common feature that causes chirality in organic molecules?	The presence of a chiral center (carbon atom bonded to four different groups).
68	What are Enantiomers?	Non-superimposable mirror images of each other (optically active).
69	What is Racemic Mixture?	An equimolar mixture of dextrorotatory (+−) and laevorotatory (−) enantiomers (optically inactive).
70	What is Retention of Configuration?	The spatial arrangement of groups around the chiral center remains the same during a reaction.
71	What is Inversion of Configuration (Walden Inversion)?	The spatial arrangement of groups around the chiral center is reversed during a reaction.
72	What is Racemisation?	The conversion of an optically active compound into an optically inactive racemic mixture.
73	Which substitution mechanism (SN1 or SN2) results in Racemisation?	SN1 (due to the planar carbocation intermediate).
74	Which substitution mechanism (SN1 or SN2) results in Inversion of Configuration?	SN2 (due to backside attack).
75	In an SN2 reaction, how does the transition state look?	A single transition state where the nucleophile and the leaving group are partially bonded to the carbon.
76	In an SN1 reaction, how many steps are involved?	Two steps (formation of carbocation followed by nucleophilic attack).
77	Which step is the rate-determining step in the SN1 mechanism?	The first step (formation of the carbocation).
78	What is the overall order of the SN2 reaction?	Second Order (rate depends on [Substrate]1 and [Nucleophile]1).
79	What is the overall order of the SN1 reaction?	First Order (rate depends only on [Substrate]1).

Part 6: Miscellaneous and Hybridization

Q. No.	Question	Answer
80	What is the use of Curved Arrows in reaction mechanisms?	To show the movement of electron pairs (or single electrons for radicals).
81	What does a Double-Headed Curved Arrow (↷) show?	Movement of a pair of electrons (ionic reactions).
82	What does a Single-Headed Curved Arrow (Fishhook Arrow, ⇀) show?	Movement of a single electron (free radical reactions).
83	What is the hybridization of the C atom in CH3​OH?	sp3.
84	What is the hybridization of the C atom in CH3​COCH3​ (Acetone)?	sp2 (for the carbonyl C) and sp3 (for the CH3​ groups).
85	Why is the C atom in a C=O bond electrophilic?	Because O is more electronegative, it creates a partial positive charge on the C atom.
86	How does increasing the s-character affect the stability of a carbanion?	Increases the stability (due to greater electron-withdrawing power).
87	Which is more stable: Vinyl carbocation (CH2​=CH+) or Ethyl carbocation (CH3​CH2+​)?	Ethyl Carbocation (Vinyl is unstable due to electron-withdrawing sp2 C).
88	What is the stability order of carbanions based on hybridization?	sp>sp2>sp3.
89	What type of electronic displacement occurs in phenol (C6​H5​OH)?	+M effect of OH group and Resonance.
90	What are the positions in the benzene ring activated by a +M group?	Ortho and Para positions (electron density increases here).
91	What are the positions in the benzene ring deactivated by a −M group?	Ortho and Para positions (electron density decreases here).
92	What is the geometry of the intermediate in an E2 reaction?	Single transition state (not an isolable intermediate).
93	What is the geometry of the intermediate in an E1 reaction?	Carbocation (sp2, Trigonal Planar).
94	What is the term for the process of converting an optically active isomer into a racemic mixture?	Racemisation.
95	How does the stability of a carbocation affect the rate of the SN1 reaction?	Higher stability leads to a faster rate.
96	Why does CHCl3​ not give the characteristic test for chlorine with AgNO3​?	The C-Cl bond is covalent and does not ionize to release Cl− ions.
97	Which effect is responsible for the activation of the ortho and para positions in toluene (C6​H5​CH3​)?	Hyperconjugation (of the CH3​ group).
98	Define Chromatography (briefly).	A technique for separating components of a mixture based on their differential partitioning between a stationary and a mobile phase.
99	What is the purpose of Lassaigne's Test?	To convert elements like N,S,X in organic compounds from covalent to ionic form for easy detection.
100	What is the Prussian blue color test used to confirm in Lassaigne's extract?	The presence of Nitrogen (CN− converted to Fe4​[Fe(CN)6​]3​).
101	Which method is suitable for the purification of aniline?	Steam Distillation (aniline is steam volatile and immiscible with water).
102	What is the principle of Distillation?	Separation based on the difference in boiling points of components.
103	What is the key difference between Distillation and Fractional Distillation?	Fractional is used when boiling points are close; simple is when they are far apart.
104	What is the purpose of using a Separating Funnel?	To separate two immiscible liquids (e.g., oil and water).

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