Isomerism Master Q&A: 300+ Questions for JEE & NEET | Chemca.in

Organic Chemistry Master Series

Isomerism Master Q&A Hub

Strictly compiled 314 Questions and Answers for Structural, Optical, Geometrical, and Conformational Isomerism.

Structural (105) Optical (104) Geo & Conform (105)

100 Q&A on Isomerism in Organic Chemistry (JEE/NEET Focus)

Part 1: Basic Concepts and Structural Isomerism

Q. No.	Question	Answer
1	Define Isomers.	Compounds having the same molecular formula but different physical or chemical properties.
2	What is Structural Isomerism?	Isomers having the same molecular formula but different connectivity (sequence of bonding).
3	What are the five main types of structural isomerism?	Chain, Position, Functional, Metamerism, and Tautomerism.
4	Define Chain Isomerism.	Isomers differing in the arrangement of the carbon skeleton (straight chain vs. branched chain).
5	Give one example of chain isomers ($C_5H_{12}$).	n-Pentane and Isopentane (2-Methylbutane).
6	Define Position Isomerism.	Isomers differing in the position of the functional group or substituent on the same carbon chain.
7	Give one example of position isomers ($C_3H_7Cl$).	1-Chloropropane and 2-Chloropropane.
8	Define Functional Isomerism.	Isomers having the same molecular formula but different functional groups.
9	Give the common functional isomer of Alcohol ($C_2H_6O$).	Ether (Dimethyl ether).
10	Give the common functional isomer of Aldehyde ($C_3H_6O$).	Ketone (Acetone).
11	Give the common functional isomer of Carboxylic Acid.	Ester ($RCOOR'$).
12	Give the common functional isomer of Alkene.	Cycloalkane.
13	Give the common functional isomer of Alkyne.	Diene (two double bonds) or Cycloalkene.
14	Define Metamerism.	Isomers differing in the nature of the alkyl groups attached to the same polyvalent functional atom/group (e.g., Ether, Ketone).
15	Give one example of metamers ($C_4H_{10}O$).	Diethyl ether and Methyl propyl ether.
16	Define Tautomerism.	Isomers existing in dynamic equilibrium due to the migration of a proton (usually between C and O or N).
17	What is the most common type of Tautomerism?	Keto-Enol Tautomerism.
18	What is the difference between an enol form and a keto form?	Enol has a hydroxyl (OH) group attached to a C=C bond; Keto has a carbonyl (C=O) group.
19	What property stabilizes the enol form of compounds like ethyl acetoacetate?	Intramolecular Hydrogen Bonding (chelation).
20	How many structural isomers are possible for $C_4H_{10}$?	Two (n-Butane and Isobutane).
21	How many structural isomers are possible for $C_5H_{12}$?	Three (n-Pentane, Isopentane, and Neopentane).

Part 2: Introduction to Stereoisomerism

Q. No.	Question	Answer
22	Define Stereoisomerism.	Isomers having the same molecular formula and connectivity but a different spatial arrangement of atoms/groups.
23	What are the two main types of stereoisomerism?	Conformational and Configurational (Geometrical and Optical).
24	Define Configurational Isomerism.	Isomers that cannot be interconverted by simple rotation around a single bond (requires bond breaking).
25	Define Geometrical Isomerism (Cis-Trans Isomerism).	Stereoisomerism arising due to restricted rotation around a double bond or in a ring structure.
26	What is the minimum structural requirement for a compound to show Geometrical Isomerism?	The two atoms/groups attached to each carbon of the double bond must be different (a $\neq$ b and c $\neq$ d in abC=cd).
27	What is a Cis Isomer?	The identical groups or atoms are on the same side of the double bond or ring.
28	What is a Trans Isomer?	The identical groups or atoms are on the opposite sides of the double bond or ring.
29	Which geometrical isomer is generally more stable and why?	Trans isomer, due to lower steric repulsion between the bulkier groups.
30	Does Propene ($CH_3CH=CH_2$) show geometrical isomerism?	No, the C-2 carbon is attached to two identical H atoms.
31	Does But-2-ene ($CH_3CH=CHCH_3$) show geometrical isomerism?	Yes (Cis and Trans forms are possible).
32	What is the alternative nomenclature system for geometrical isomers when groups are different (abC=cd)?	E/Z System (E = Entgegen, Z = Zusammen).
33	What rule is used to assign priority to groups in the E/Z system?	Cahn-Ingold-Prelog (CIP) Rules.
34	How are the Z and Cis isomers related in a simple case like But-2-ene?	Z is equivalent to Cis (highest priority groups on the same side).
35	How are the E and Trans isomers related in a simple case like But-2-ene?	E is equivalent to Trans (highest priority groups on opposite sides).
36	Does Cyclopropane show geometrical isomerism?	Yes, if there are two different substituents on any two carbon atoms.
37	Which geometrical isomer of But-2-enedioic Acid (HOOC-CH=CH-COOH) is more acidic?	Maleic Acid (Cis isomer), due to intramolecular H-bonding stabilizing the monoanion.
38	What is the name of the Trans isomer of But-2-enedioic Acid?	Fumaric Acid.
39	Does Oxime (R-CH=N-OH) show geometrical isomerism?	Yes (due to restricted rotation around the C=N bond, called Syn/Anti isomerism).

Part 3: Relationship between Properties and Isomerism

Q. No.	Question	Answer
40	Why does the Cis isomer often have a higher dipole moment than the Trans isomer?	Dipoles often add up in the Cis form, but cancel out in the Trans form (due to symmetry).
41	Which isomer of 1,2-dichloroethene (ClCH=CHCl) has a net dipole moment of zero?	Trans isomer (dipoles cancel).
42	Which isomer of 1,2-dichloroethene has the higher boiling point?	Cis isomer (higher BP due to higher polarity/dipole moment).
43	Which isomer of 1,2-dichloroethene has the higher melting point?	Trans isomer (higher MP due to better packing in the crystal lattice).
44	What is the term for the stability gained by the enol form in tautomerism?	Intramolecular Hydrogen Bonding (chelation).
45	How does tautomerism affect the reactivity of a compound?	It leads to a mixture of isomers, and the reaction proceeds through the more reactive tautomer.
46	Can a compound exhibit both Functional and Position isomerism?	No, they are distinct categories based on structural differences.
47	How is the DBE (Double Bond Equivalent) of a compound related to its structural possibilities?	DBE gives the number of rings and/or $\pi$-bonds required for the formula.
48	What is the relationship between the number of isomers and the size of the carbon chain?	The number of possible isomers increases rapidly as the carbon chain length increases.
49	What type of isomerism is shown by But-1-yne and But-2-yne?	Position Isomerism (position of the triple bond changes).

Part 4: JEE/NEET Application and Advanced Concepts

Q. No.	Question	Answer
50	What is the geometrical configuration of the two double bonds in Hepta-2,4-diene?	Cis/Trans possibilities at both C-2 and C-4 (resulting in four stereoisomers).
51	What are Syn and Anti Isomers?	Geometrical isomers specifically used for oximes (C=N bond) instead of Cis/Trans.
52	In Syn/Anti Isomerism, what determines the nomenclature?	Syn when H on C and OH on N are on the same side; Anti when on the opposite side.
53	Does Allene ($CH_2=C=CH_2$) show geometrical isomerism?	No, the two $\pi$-bonds are perpendicular, preventing planar arrangements.
54	How many stereoisomers does 1-bromo-1-chloro-propene ($CH_3CH=C(Br)Cl$) have?	Two (Geometrical E/Z isomers only).
55	What is the maximum number of geometrical isomers possible for a compound with n identical double bonds?	Generally $2^n$ (if n is the number of double bonds that can exhibit GI).
56	What are Conformers?	Stereoisomers that can be interconverted by rotation around a single bond (e.g., staggered and eclipsed ethane).
57	What is the maximum angle of rotation required to interconvert geometrical isomers?	180° rotation around the double bond (which requires bond breaking/high energy).
58	Which isomer (Cis or Trans) reacts faster with $KMnO_4$ (hydroxylation) and why?	Cis isomer is often slower, as its bulky groups can hinder the approach of the reagent.
59	How many pairs of Cis/Trans isomers are possible in Octa-2,4,6-triene?	Eight ($2^3=8$ total stereoisomers, 4 pairs of diastereomers, including Cis/Trans).

Part 5: More Structural Isomerism Examples

Q. No.	Question	Answer
60	What type of isomerism is exhibited by Propanal and Propanone?	Functional Isomerism (Aldehyde vs Ketone).
61	What type of isomerism is exhibited by 1-Butyne and Buta-1,3-diene?	Functional Isomerism (Alkyne vs Diene).
62	What type of isomerism is exhibited by Propan-1-ol and Propan-2-ol?	Position Isomerism.
63	What type of isomerism is exhibited by Butanoic Acid and Ethyl Ethanoate?	Functional Isomerism (Acid vs Ester).
64	What type of isomerism is exhibited by Propylamine ($CH_3CH_2CH_2NH_2$) and Ethylmethylamine ($CH_3CH_2NHCH_3$)?	Functional Isomerism (1° vs 2° amine).
65	What type of isomerism is exhibited by Propanal and Cyclopropanol ($C_3H_6O$)?	Ring-Chain Isomerism (also functional isomerism if viewed broadly).
66	What type of isomerism is exhibited by Pent-1-ene and Cyclopentane ($C_5H_{10}$)?	Ring-Chain Isomerism (also functional).
67	What type of isomerism is exhibited by Butanone and Diethyl Ketone?	Metamerism (Ketone group position).
68	Give one example of a compound showing Keto-Enol Tautomerism.	Acetone ($CH_3COCH_3$) or Acetaldehyde ($CH_3CHO$).
69	What is the formula to calculate the number of chain isomers for alkanes?	No simple formula, usually solved by drawing structures.

Part 6: More Geometrical Isomerism Scenarios

Q. No.	Question	Answer
70	Does 1,1-Dichloroethene ($Cl_2C=CH_2$) show geometrical isomerism?	No, the C-1 carbon has two identical Cl atoms.
71	Does Cyclohexane show geometrical isomerism?	No, but its disubstituted derivatives (e.g., 1,2-Dimethylcyclohexane) do.
72	What is the relationship between Cis-1,2-Dimethylcyclopropane and Trans-1,2-Dimethylcyclopropane?	They are Diastereomers (and geometrical isomers).
73	Assign the configuration (E or Z) to 1-bromo-1-chloro-propene where Br and H are Cis.	Z (Br on C-1 and $CH_3$ on C-2 are highest priority; if they are Cis $\rightarrow$ Z).
74	What is the name given to isomers that are neither Cis nor Trans but are E/Z isomers?	Diastereomers.
75	How many E/Z isomers are possible for 3-Hexene?	Two (E and Z).
76	Can a compound exhibit both Geometrical and Optical isomerism?	Yes, if it has both restricted rotation and a chiral center.
77	In the E/Z system, what does the letter 'Z' mean?	Zusammen (Together/Same side).
78	In the E/Z system, what does the letter 'E' mean?	Entgegen (Opposite side).
79	What is the most common reason for the Trans isomer being generally more stable?	Reduced Steric Strain.
80	Give an example of a cyclic compound showing geometrical isomerism.	1,2-Dimethylcyclobutane (Cis/Trans).

Part 7: Tautomerism and Isomerism in Functional Groups

Q. No.	Question	Answer
81	What is the term for the migration of the proton in tautomerism?	Prototropy.
82	What type of isomerism is shown by Methylacetylene ($CH_3C\equiv CH$) and Allene ($CH_2=C=CH_2$)?	Functional Isomerism (Alkyne vs Allene).
83	What type of isomerism is exhibited by 1°, 2°, and 3° Amines ($C_3H_9N$)?	Functional Isomerism.
84	What type of isomerism is exhibited by Di-n-propylamine and Ethyl-n-butylamine ($C_6H_{15}N$)?	Metamerism (2° amines with different alkyl groups).
85	Why is the Keto form generally more stable than the Enol form?	The C=O bond is much stronger than the C=C bond.
86	Which Carbonyl compound exists almost entirely in the enol form and why?	Phenol (due to aromatic stabilization of the enol form).
87	Does Benzaldehyde show Keto-Enol tautomerism?	No, it lacks an $\alpha$-hydrogen.
88	Does Tautomerism affect the chemical properties of a compound?	Yes, as the minor tautomer might be the one that reacts (reaction proceeds via the most reactive species).
89	What type of isomerism is shown by Cyclohexane and Hex-1-ene?	Ring-Chain and Functional Isomerism.
90	What are the general structural formulas for Metamers in the Ketone family?	R-C=O-R' and R''-C=O-R''' where R+R'=R''+R'''.

Part 8: Final Applications and Revision

Q. No.	Question	Answer
91	What is the DBE (Degree of Unsaturation) for $C_6H_6$?	4 (3 double bonds and 1 ring).
92	How many structural isomers are possible for Dichlorobenzene ($C_6H_4Cl_2$)?	Three (o-, m-, p-).
93	How many Cis/Trans isomers does 1,2-dibromocyclobutane have?	Three (Cis and two optically active Trans forms).
94	What is the stability order of conformations in cyclohexane?	Chair > Twist-boat > Boat > Half-chair.
95	Does 1,1-Dimethylcyclohexane show geometrical isomerism?	No, as the C-1 carbon has two identical $CH_3$ groups.
96	Name the type of isomerism responsible for the high boiling point of Cis alkenes.	Geometrical Isomerism (leading to higher polarity).
97	What is the relationship between the Cis/Trans pair of But-2-ene?	They are Diastereomers.
98	In Oximes, if the H on C and OH on N are Anti, what is the Cis/Trans equivalent?	Trans equivalent.
99	How many total stereoisomers are possible for 3-chloro-4-fluoro-2-pentene?	Four (One C=C for GI, two chiral centers for OI).
100	What is the total number of Cis/Trans isomers for 2,4-Hexadiene?	Three (Cis-Cis, Trans-Trans, and Cis-Trans $\equiv$ Trans-Cis).
101	What is the structural requirement for an alicyclic compound to exhibit geometrical isomerism?	Presence of at least two different substituents on two different ring carbon atoms.
102	What is the relationship between the two Chair conformations of cyclohexane?	They are Conformational Isomers (easily interconvertible).
103	Which type of isomerism is responsible for the unique properties of Fructose (a Ketose) and Glucose (an Aldose)?	Functional Isomerism ($C_6H_{12}O_6$).
104	What is the condition for a Metamer to be possible in the Ether series?	The ether must have at least four carbon atoms in total (e.g., $C_4H_{10}O$).
105	What kind of isomerism is observed between 2-pentene (C=C at C-2) and 1-pentene (C=C at C-1)?	Position Isomerism.

2. Over 100 Q&A for Optical Isomerism (104 Questions)

Part 1: Fundamentals and Chiral Molecules

Q. No.	Question	Answer
1	Define Optical Isomerism.	Isomerism where compounds have the same molecular formula but differ in their effect on plane-polarized light (PPL).
2	What is Plane-Polarized Light (PPL)?	Light waves oscillating in only one single plane.
3	What is a Polarimeter?	The instrument used to measure the angle of rotation of PPL caused by an optically active substance.
4	Define an Optically Active substance.	A substance that rotates the plane of PPL when passed through its solution or pure liquid form.
5	Define an Optically Inactive substance.	A substance that does not rotate the plane of PPL.
6	What does the prefix Dextrorotatory (d or +) signify?	Rotation of PPL to the Right (clockwise).
7	What does the prefix Laevorotatory (l or −) signify?	Rotation of PPL to the Left (anticlockwise).
8	Define Specific Rotation ($\alpha$)	The angle of rotation produced by a solution of concentration 1 g/mL in a tube of 1 dm length.
9	Define a Chiral Molecule.	A molecule that is non-superimposable on its mirror image.
10	Define an Achiral Molecule.	A molecule that is superimposable on its mirror image.
11	What is the necessary and sufficient condition for a molecule to be chiral?	Absence of a Plane of Symmetry ($\sigma$) or Center of Symmetry (i).
12	What is a Chiral Centre?	An atom (usually Carbon) bonded to four different atoms or groups.
13	Why is Glycine ($H_2NCH_2COOH$) optically inactive?	Its $\alpha$-carbon is attached to two H atoms (it lacks a chiral centre).
14	What is the term for a carbon atom bonded to four different groups?	Asymmetric Carbon or Chiral Carbon.
15	What is the total number of stereoisomers for a molecule with n different chiral centres?	$2^n$ (van't Hoff rule, max possible stereoisomers).

Part 2: Enantiomers, Diastereomers, and Meso Compounds

Q. No.	Question	Answer
16	Define Enantiomers.	Stereoisomers that are non-superimposable mirror images of each other.
17	How do enantiomers differ in their physical properties?	They have identical physical properties (melting point, boiling point, solubility, refractive index, etc.).
18	How do enantiomers differ in their optical activity?	They rotate PPL by the same magnitude but in opposite directions (+ and −).
19	Define a Racemic Mixture (dl or $\pm$).	An equimolar mixture of two enantiomers.
20	Is a racemic mixture optically active or inactive?	Optically inactive (external compensation/cancellation of rotations).
21	Define Racemisation.	The process of converting a pure enantiomer into a racemic mixture.
22	Define Diastereomers.	Stereoisomers that are not mirror images of each other.
23	How do diastereomers differ in their physical properties?	They have different physical properties (can be separated by fractional distillation or crystallization).
24	Define a Meso Compound.	An optically inactive compound despite having chiral centres.
25	What is the structural condition for a meso compound?	It must possess a Plane of Symmetry ($\sigma$) or a Center of Symmetry (i).
26	What type of compensation leads to the optical inactivity of a meso compound?	Internal Compensation (one half of the molecule rotates light equally and oppositely to the other half).
27	How many stereoisomers are possible for Tartaric Acid (2,3-dihydroxybutanedioic acid)?	Three (one d, one l, and one meso form).
28	What is the relationship between the meso form and its enantiomers (the d and l forms)?	The meso form is a diastereomer of the d and l forms.
29	What is the formula for calculating the number of meso forms possible for a symmetric molecule?	$2^{(n/2)−1}$ (where n is the number of chiral centres, if n is even).

Part 3: R/S Nomenclature (CIP Rules)

Q. No.	Question	Answer
30	What is the R/S System used for?	To give an absolute configuration to each chiral centre.
31	What does the letter R signify in R/S nomenclature?	Rectus (Latin for Right).
32	What does the letter S signify in R/S nomenclature?	Sinister (Latin for Left).
33	What is the fundamental principle of the CIP Rules?	Assigning priority to the four groups attached to the chiral centre based on Atomic Number.
34	How are isotopes prioritized in the CIP rules?	The higher mass number isotope gets higher priority (e.g., D > H).
35	How are double/triple bonds treated in the CIP rules?	The multiply-bonded atom is counted as being bonded to an equivalent number of single-bonded atoms (fictitious atoms).
36	How is configuration determined if the lowest priority group (4) is pointing away (dashed)?	R for clockwise rotation (1→2→3), S for anticlockwise.
37	How is configuration determined if the lowest priority group (4) is pointing towards the observer (wedge)?	The determined configuration (from 1→2→3) is Inverted (R→S and vice versa).
38	What is the relationship between R and S forms?	They are Enantiomers.

Part 4: Chirality in Reactions and Resolution

Q. No.	Question	Answer
39	What is the stereochemical result of a nucleophilic substitution reaction ($S_N1$) on a chiral substrate?	Racemisation (or partial racemisation).
40	What is the stereochemical result of a nucleophilic substitution reaction ($S_N2$) on a chiral substrate?	Inversion of Configuration (Walden Inversion).
41	When does Walden Inversion occur?	When the nucleophile attacks from the backside of the leaving group ($S_N2$ mechanism).
42	Define Resolution.	The process of separating a racemic mixture into its constituent pure enantiomers.
43	Why can't enantiomers be separated by fractional distillation?	They have identical boiling points.
44	What is the standard method for resolving a racemic mixture?	Conversion to Diastereomeric Salts, separation by crystallization, and then regeneration of the enantiomers.
45	Why can diastereomeric salts be separated easily?	They have different physical properties (solubility, melting point).
46	What is the term for a molecule that rotates PPL but has no chiral centre (e.g., substituted allenes)?	Axial Chirality.
47	Give an example of a common resolving agent.	An optically active acid (+ Tartaric acid) or base (+ Strychnine).

Part 5: Symmetry Elements and Optical Activity

Q. No.	Question	Answer
48	Define a Plane of Symmetry ($\sigma$).	An imaginary plane that divides the molecule into two identical halves that are mirror images of each other.
49	Define a Centre of Symmetry (i).	A point within the molecule from which lines drawn to identical atoms are equal in length but opposite in direction.
50	Does a molecule with a centre of symmetry exhibit optical activity?	No, it is achiral.
51	Does a molecule with a chiral centre always exhibit optical activity?	No (the exception is the meso compound).
52	What is a Stereogenic Centre?	Any point in a molecule where the interchange of two groups leads to a stereoisomer (includes chiral centre and C=C double bond).
53	Which form of cyclohexane is achiral due to a plane of symmetry?	Trans-1,4-disubstituted cyclohexane.
54	Relationship between stability of eclipsed butane and optical activity?	Conformations are interconvertible, so overall molecule is inactive.

Part 6: Quickfire Revision and Numerical Application

Q. No.	Question	Answer
55	Configuration of C-2 in L-Glyceraldehyde?	S (S-configuration).
56	Configuration of C-2 in D-Glyceraldehyde?	R (R-configuration).
57	Stereoisomers for 2-chlorobutane?	Two (a single pair of enantiomers, $2^1$).
58	Max stereoisomers for 2,3-dichlorobutane?	Four ($2^2$), but only three unique (due to meso form).
59	Chiral centres in Glucose?	Four chiral centres.
60	Term for non-mirror stereoisomers rapidly interconverting?	Conformers.
61	Mixture of 75% R and 25% S enantiomeric excess (ee)?	50% (ee = 75 − 25).
62	If ee is 80%, percentage of major enantiomer?	90% (Major = 50 + ee/2).
63	Is the product of $H_2$ addition to Cis-But-2-ene chiral?	No, the product (Butane) is achiral.
64	Result of Butan-2-ol + HBr ($S_N1$)?	Racemic Mixture.
65	Separation of racemic mixture is called...	Resolution.
66	Chemical that rotates PPL is...	Optically Active Substance.
67	Simplest chiral alkane?	3-Methylhexane ($C_7H_{16}$).
68	Simplest chiral alcohol?	Butan-2-ol ($C_4H_{10}O$).
69	Relationship between D-Glucose and L-Glucose?	Enantiomers.
70	Relationship between D-Glucose and D-Mannose?	Diastereomers (specifically, C-2 epimers).
71	What are Epimers?	Diastereomers that differ in configuration at only one chiral centre.
72	Common name for D/L system based on Glyceraldehyde?	Fischer Projection (relative configuration).
73	Is rotation related to R/S configuration?	No, R does not imply + and S does not imply −.
74	$\alpha$ and $\beta$ forms of Glucose?	Anomers (specific type of diastereomer).
75	How to check for centre of symmetry?	Reflect every atom through the center point.

Part 7: Optical Isomerism in Rings and Other Systems

Q. No.	Question	Answer
76	Does Cis-1,2-Dimethylcyclopropane have a plane of symmetry?	Yes (a plane perpendicular to the ring).
77	Is Cis-1,2-Dimethylcyclopropane optically active?	No (it is a meso compound / achiral).
78	Does Trans-1,2-Dimethylcyclopropane have a plane of symmetry?	No.
79	Is Trans-1,2-Dimethylcyclopropane optically active?	Yes (it exists as a pair of enantiomers).
80	What is a Pseudochiral Centre?	A carbon atom bonded to four different groups, two of which are enantiomers of each other.
81	Configuration of C-3 in Meso-Tartaric Acid?	Lower case r or s (depends on other chiral center).
82	Enantiomer dissolved in non-chiral solvent activity?	No change (remains optically active).
83	Enantiomer mixed with mirror image activity?	Inactive (racemic mixture).
84	Term for stability of racemic mixture?	External compensation (thermodynamic stability).
85	Can compounds with double bonds show optical activity?	Yes, via axial chirality (allenes) or other chiral centres.

Part 8: Final Applications (Q86-104)

Q. No.	Question	Answer
86	Stereoisomers for 2,3,4-trichlorohexane?	Eight ($2^3=8$) as chiral centres are non-identical.
87	Rotation of 1:3 d and l mixture (pure enantiomer = +50°)?	−25° (ee = 25% l, so 0.5 × 50°).
88	Strain minimized in anti Fisher projections?	Torsional strain.
89	Reduction of Acetophenone by $NaBH_4$ product chiral?	Yes (1-phenylethanol is chiral).
90	Reason for inactivity of D- and L-tartaric acid solution?	External compensation.
91	R/S configuration of C-2 in L-Alanine?	S.
92	Relationship between d/l and D/L notation?	d/l = rotation; D/L = relative configuration.
93	Plane of symmetry in Fischer Projection?	Check plane that bisects vertically or horizontally.
94	Syn addition of $Br_2$ to alkene?	Both atoms add to the same face.
95	Anti addition of $Br_2$ to alkene?	Atoms add to opposite faces.
96	Does Trans-1,3-dimethylcyclohexane show optical activity?	Yes (it is chiral).
97	Converting pure enantiomer to racemic is...	Racemisation.
98	Why are meso compounds possible with even chiral centres?	Allows for internal plane of symmetry.
99	Simplest molecule exhibiting optical isomerism?	Glyceraldehyde ($C_3H_6O_3$).
100	Are Cis/Trans isomers also optical isomers?	No, they are diastereomers (geometrical).
101	What is a chiroptical property?	Molecular property related to chiral asymmetry.
102	R/S configuration of D-lactic acid?	R.
103	Relationship between chair forms of Trans-1-tert-butyl-4-methylcyclohexane?	Conformers.
104	Reaction producing single enantiomer from non-chiral?	Asymmetric Synthesis.

3. Geometrical and Conformational Isomerism (105 Questions)

Part 1: Fundamentals & Alkenes

Q. No.	Question	Answer
1	Fundamental requirement for GI?	Restricted rotation around a bond (double bond or ring).
2	Structural requirement for GI around C=C?	Each carbon of double bond attached to two different groups.
3	What is a Cis-isomer?	Identical groups on the same side.
4	What is a Trans-isomer?	Identical groups on opposite sides.
5	Why does Propene not show GI?	Identical H atoms on C-1.
6	Relationship between Cis and Trans?	Diastereomers.
7	Which geometrical isomer more stable?	Trans, due to lower steric repulsion.
8	Dipole moment effect in GI?	Cis ($\mu \neq 0$), Trans ($\mu = 0$ if symmetric).
9	Higher BP isomer of 1,2-dichloroethene?	Cis (higher polarity).
10	Higher MP isomer of 1,2-dichloroethene?	Trans (better packing).
11	GI in Cycloalkenes restriction?	Small rings only Cis; $\geq 8$ carbons can be stable Trans.
12	Does 1,1-Dichloroethene show GI?	No.
13	GI shown by But-2-ene?	Cis (Z) and Trans (E).
14	Anti-addition of $Br_2$ to Cis-but-2-ene?	meso-2,3-dibromobutane.
15	Anti-addition of $Br_2$ to Trans-but-2-ene?	Racemic mixture of d,l-2,3-dibromobutane.
16	E/Z system purpose?	Configuration for isomers with multiple substituents.
17	Meaning of Z?	Zusammen (Together).
18	Meaning of E?	Entgegen (Opposite).
19	Priority rule for E/Z?	CIP Rules.
20	E/Z priority basis?	Atomic Number.
21	Highest groups same side?	Z.
22	Highest groups opposite sides?	E.
23	Does Propanone Oxime show GI?	No.
24	Oxime GI names?	Syn and Anti.
25	Does Cyclohexane show GI?	Only in disubstituted derivatives.
26	1,2-Dimethylcyclopropane isomers?	Cis and Trans.
27	Cis vs Trans 1,2-dimethylcyclohexane?	Diastereomers.
28	GI for Hepta-2,4-diene?	Four ($2^2$).
29	GI for But-2-yne?	Zero (Linear geometry).
30	Does Allene show GI?	No.
31	Define Conformational Isomerism.	Interconvertible by single bond rotation.
32	Other names for Conformers?	Conformers or Rotamers.
33	Preferred representation for conformations?	Newman Projections.
34	Define Torsional Strain.	Repulsive strain due to proximity of adjacent bond electron clouds.
35	Ethane max stability form?	Staggered.
36	Ethane min stability form?	Eclipsed.
37	Energy difference term?	Torsional energy ($\approx 12.5$ kJ/mol).
38	Staggered Ethane dihedral angle?	60°.
39	Eclipsed Ethane dihedral angle?	0°.
40	Why not isolated at room temp?	Low interconversion energy barrier.
41	Most stable Butane conformation?	Anti-staggered (180°).
42	Least stable Butane conformation?	Fully Eclipsed (0°).
43	Strain across space term?	Steric Strain.
44	Between anti and eclipsed form?	Gauche (60°).
45	Gauche/Anti energy difference cause?	Steric hindrance ($CH_3/CH_3$ interaction).
46	Perfectly planar cycloalkane?	Cyclopropane (60°).
47	Cause of instability in $C_3$ and $C_4$ rings?	Angle Strain and Torsional Strain.
48	Stable non-planar Cyclobutane form?	Puckered/Folded.
49	Most stable Cyclopentane form?	Envelope.
50	Most stable Cyclohexane form?	Chair form.
51	Types of C-H bonds in Chair form?	Axial and Equatorial.
52	Chair-Chair interconversion name?	Ring flipping.
53	Effect of ring flipping on bonds?	Axial $\leftrightarrow$ Equatorial.
54	Highest energy Cyclohexane form?	Half-chair.
55	Stable after Chair form?	Twist-boat.
56	H at C-1 and C-4 in boat?	Flagpole Hydrogens.
57	Monosubstituted stability position?	Equatorial (avoids 1,3-diaxial strain).
58	1,3-Diaxial Interaction?	Steric repulsion between axial C-1 group and axial H at C-3, C-5.
59	Axial methyl 1,3-diaxial count?	Two.
60	Relationship between chair forms of methylcyclohexane?	Diastereomers.
61	Stereoisomers for 1,3-Dichlorocyclopentane?	Three (Cis [achiral] + pair of Trans [enantiomers]).
62	GI for A-CH=CH-CH=CH-B?	Possible at both C-2 and C-4.
63	Max stereoisomers for Hepta-2,4-diene?	Four ($2^2$).
64	Cis/Trans rotation relationship?	Configurational (not easily rotatable).
65	Gauche vs Anti Butane?	Conformational Isomers (Rotamers).
66	Does Allene show GI?	No.
67	Isomer formed in E2 elimination?	Trans isomer (Saytzeff's major).
68	Ring-flipping energy in cyclohexane?	$\approx 42-45$ kJ/mol.
69	1,2-Dimethylcyclohexane meso form?	Cis isomer.
70	Which C=C bond is shorter?	Essentially same length.
71	Flagpole interaction cause?	Steric repulsion.
72	Gauche stability in 2-chloroethanol term?	Intramolecular H-bonding.
73	Max eclipsed interactions in ethane?	Three.
74	Major strain in Chair form?	None (minimal angle/torsional strain).
75	Why Twist-boat > Boat stability?	Less torsional strain; avoids flagpole interaction.
76	Hydration speed: maleic vs fumaric acid?	Maleic (cis) hydrates faster.
77	Size effect on axial/equatorial?	Preference for Equatorial increases with size.
78	Cyclohexane strain primary cause?	Torsional/Steric in boat; angle strain negligible in chair.
79	Geometrical isomers for 1,3-Dimethylcyclohexane?	Four (Cis and Trans pairs of enantiomers).
80	Acetophenone Oxime bond configuration?	Syn and Anti.
81	Relationship: Cis/Trans 1,3-Dimethylcyclohexane?	Diastereomers.
82	Higher $pKa$ isomer of But-2-enoic acid?	Trans (Fumaric).
83	Ring size effect on Trans cycloalkenes?	Stable only as ring size increases.
84	Boat conformer activity?	Inactive (contains plane of symmetry).
85	Preferred form of Trans-1,4-dibromocyclohexane?	Diequatorial (e,e) chair.
86	Does Buta-1,3-diene show GI?	No.
87	Rotation of axial H bonds towards center?	Axial-Axial interaction.
88	GI isomers for 1-chloro-1-propene?	Two (Cis and Trans).
89	E2 product of menthyl chloride?	Anti-Saytzeff (requires anti-periplanar geometry).
90	Is Cyclooctene capable of GI?	Yes, smallest for which Trans is stable.
91	Is GI molecule always achiral?	No.
92	Chair vs Boat energy difference?	$\approx 29$ kJ/mol.
93	Separation method for GI?	Fractional distillation.
94	GI nomenclature for azo bonds?	Syn/Anti.
95	Stable form of Buta-1,3-diene?	s-Trans.
96	Anti Butane dihedral angle?	180°.
97	Gauche Butane dihedral angle?	60°.
98	Why eclipsed less stable?	Torsional Strain.
99	Chair vs Twist-boat relationship?	Conformational Isomers.
100	Cis But-2-enedioic Acid name?	Maleic Acid.
101	Trans But-2-enedioic Acid name?	Fumaric Acid.
102	Stereoisomers: 1 double bond + 1 chiral center?	Four ($2 \times 2 = 4$).
103	Method to analyze conformations?	Conformational Analysis.
104	Smallest isolable Trans cycloalkene?	Trans-Cyclooctene ($C_8$).
105	Min carbons for alkene GI?	Four (But-2-ene).

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Complete isomerism in organic chemistry