ORGANIC CHEMISTRY

ISOMERISM

H D
CH3
D
CH3 H
H H
D CH3 H3C D

D CH3 H3C D
H H

We look different, but are we really different ?

Do better than yourself, beat your own records everyday and pray to God for a better tomorrow
Success will chase you....
 EXERCISE-I
Q.1 The number of primary, secondary and tertiary amines possible with the molecular formula C 3H9N
respectively.
(A) 1, 2, 2 (B) 1, 2, 1 (C) 2, 1, 1 (D) 3, 0, 1

Br COOH COOH Br

Q.2 and are

HOOC Br Br COOH

(A) Positional (B) Chain (C) Geometrical (D) Functional

Q.3 Only two isomeric monochloro derivatives are possible for (excluding stereo)
(A) n-butane (B) 2, 2-dimethylpentane
(C) benzene (D) neopentane

Q.4 Molecular formula C5H10O can have :

(A) 6-Aldehyde, 4-Ketone (B) 5-Aldehyde, 3-Ketone
(C) 4-Aldehyde, 3-Ketone (D) 5-Aldehyde, 2-Ketone

Q.5 Molecular formula C3H6Br2 can have:

(A) Two gem dibromide (B) One vic dibromide
(C) Two ter.- dibromo alkane (D) Two sec.-dibromo alkane

Q.6 The number of isomers of C5H10 is

(A) 10 (B) 11 (C) 12 (D) 13

Q.7 The number of isomers of dibromoderivative of an alkene (molar mass 186 g mol–1) is
(A) 2 (B) 3 (C) 4 (D) 6

Q.8 The number of isomers of C3H5Br3 is

(A) 4 (B) 5 (C) 6 (D) 7

Q.9 Increasing order of stability among the three main conformation (i.e. eclipse, anti, gauche) of ethylene
glycol is :
(A) Eclipse, gauche, anti (B) Gauche, eclipse, anti
(C) Eclipse, anti, gauche (D) Anti, gauche, eclipse

Q.10 How many primary amines are possible for the formula C4H11N?
(A) 2 (B) 3 (C) 4 (D) 5

Q.11 The total number of isomeric optically active monochloro isopentane is:
(A) two (B) three (C) four (D) one

ISOMERISM [2]
Q.12 On chlorination of propane number of products of the formula C3H6Cl2 is
(A) 3 (B) 4 (C) 5 (D) 6

Q.13 The compounds C2H5OC2H5 and CH3OCH2CH2CH3 are

(A) chain isomers (B) geometrical isomers
(C) metamers (D) conformational isomers

COOH
OCOH
Q.14 & functional isomer

OMe OEt
Et
& metamers
Me

CH2 – CH2 – OH CH2 – O – CH3

& metamers

Me – N – Me CH2 – NH – CH3

& functional isomers

(A) TFTF (B) FTTF (C) TTFT (D) TFFT

O O
Cl C—O C—O Cl
Q.15 H and CH3
C=C C=C
H CH3 H H
Shows which type of isomerism
(A) Functional group isomerism (B) Geometrical isomerism
(C) Metamerism (D) Position isomerism

Q.16 How many minimum no. of C-atoms are required for position & geometrical isomerism in alkene?
(A) 4, 3 (B) 4, 4 (C) 3, 4 (D) 3, 3

Q.17 How many structural formula are possible when one of the hydrogen is replaced by a chlorine atom in
anthracene & phenanthracene?
(A) 3, 5 (B) 7, 3 (C) 3, 3 (D) 6, 2

Q.18 Which of the following cannot be written in an isomeric form?

(A) CH3–CH(OH)–CH2–CH3 (B) CH3–CHO
(C) CH2=CH–Cl (D) Cl–CH2CH2–Cl
ISOMERISM [3]
Q.19 Given compound shows which type of isomerism
O O
S—O S—O
and
O O
(A) Chain isomerism (B) Positional isomerism
(C) Metamerism (D) Functional group isomerism

Q.20 Which of the following does not show geometrical isomerism?

(A) 1, 2-dichloro-1-pentene (B) 1, 3-dichloro-2-pentene
(C) 1, 1-dichloro-1-pentene (D) 1, 4-dichloro-2-pentene

Q.21 The number of cis-trans isomer possible for the following compound

(A) 2 (B) 4 (C) 6 (D) 8

Q.22 Which of the following have zero dipole moment?

(A) benzene 1,4- diol (B) trans-1,2-dichloro ethene
(C) cis-1,2-dichloro ethene (D) 1,1-dichloro ethene

Q.23 What characteristic is the best common to both cis-2-butene and trans-2-butene?
(A) B.P. (B) Dipole moment
(C) heat of hydrogenation (D) Product of hydrogenation

Q.24 Geometrical isomerism is possible in:

(A) isobutene (B) acetone oxime
(C) acetophenone oxime (D) benzophenone oxime

Q.25 Which of the following will not show geometrical isomerism.

Me Me CH3
(A) (B) (C) Cl (D)
Me H

Q.26 The number of optically active compounds in the isomers of C4H9Br is

(A) 1 (B) 2 (C) 3 (D) 4

Q.27 How many stereoisomers of the following molecule are possible?

HOOC.CH=C=CH.COOH
(A) two optical isomers (B) two geometrical isomers
(C)two optical and two geometrical isomers (D) None

ISOMERISM [4]
Q.28 C7H7Cl shows how many benzenoid aromatic isomers ?
(A) 4 (B) 3 (C) 5 (D) 6

Q.29 Number of possible 3D-isomers of glucose are

(A) 10 (B) 14 (C) 16 (D) 20

Q.30 The number of optically active isomers observed in 2,3-dichlorobutane is:

(A) 0 (B) 2 (C) 3 (D) 4

Q.31 Which of the following will not show optical isomerism.

(A) Cl–CH=C=C=CH–Cl (B) Cl–CH=C=C=C=CH–Cl

(C) (D)

Q.32 The two compounds given below are

(A) enantiomers (B) identical (C) optically inactive (D) diastereomers

Q.33 Molecular weight of a hydrocarbon containing minimum number of C-atom to show optical isomerism.
(A) 100 (B) 80 (C) 68 (D) 70

Q.34 Total number of stereoisomer of following compounds are respectively.

OH OH

OH
(A) 4, 6 (B) 4, 4 (C) 6, 6 (D) 8, 8

Q.35 Tautomer in following is Diad system :

O

(A) CH3COCH3 (B) CH3CH2NO2 (C) (D) HCN

ISOMERISM [5]
 O O

Q.36

Above interconversion takes place in

(A) Acidic medium (B) Basic medium (C) Both (D) None

Q.37 Meso-tartaric acid and d-tartaric acid are

(A) positional isomers (B) enantiomers (C) diastereomers (D) racemic mixture

Q.38 How many stereoisomers can exist for the following acid
H  C(OH).CO 2 H
|
H  C.CO 2 H
|
H  C(OH).CO 2 H
(A) Two (B) Four (C) Eight (D) Sixteen

Q.39 The structure of (2R, 3S)C2H5CH(CH3)CH(D)CH2D is

(A) (B) (C) (D)

Q.40 Observe the given compounds and answer the following questions.

(i) Which of the above formulae represent identical compounds?

(A) I and II (B) I and IV (C) II and IV (D) III and IV

(ii) Which of the above compounds are enantiomers?

(A) II and III (B) III and IV (C) III and V (D) I and V

Q.41

The compound with the above configuration is called:

(A) (2S, 3S)-2-chloro-3-pentanol (B) (2S, 3R)-2-chloro-3-pentanol
(C) (2R, 3R)-2-chloro-3-pentanol (D) (2R, 3S)-2-chloro-3-pentanol

ISOMERISM [6]
Q.42 The full name of the compound is

(A) (2R,3R)-3-chloro-2-pentanol (B) (2R,3S)-3-chloro-2-pentanol

(C) (2S,3R)-3-chloro-2-pentanol (D) (2S,3S)-3-chloro-2-pentanol

Q.43 The structure of (2R, 3R)C2H5CH(CH3)CH(D)CH2D is

(A) (B) (C) (D)

Q.44 Which species exhibits a plane of symmetry?

(A) (B) (C) (D)

Q.45 What observed rotation is expected when a 1.5 M solution of (R)-2-butanol is mixed with an equal volume
of a 0.75 M solution of racemic 2-butanol and the resulting solution is analysed in a sample container that is
1 dm long? The specific rotation of (R)-2-butanol is –13.9°ml gm–1dm–1.
(A) +0.77° (B) –0.77° (C) +0.35° (D) –0.35°

Q.46 A pure sample of 2-chlorobutane shows rotation of PPL by 30° in standard conditions. When above
sample is made impure by mixing its opposite form, so that the composition of the mixture becomes
87.5% d-form and 12.5% l-form, then what will be the observed rotation for the mixture.
(A) –22.5° (B) +22.5° (C) +7.5° (D) –7.5°

Q.47 When an optically active compound is placed in a 10 dm tube is present 20 gm in a 200 ml solution
rotates the PPL by 30°. Calculate the angle of rotation & specific angle of rotation if above solution is
diluted to 1 Litre.
(A) 16° & 36° (B) 6° & 30° (C) 3° & 30° (D) 6° & 36°

Q.48 Which of the following combinations amongst the four Fischer projections represents the same absolute
configurations?

(A) (II) and (III) (B) (I) and (IV) (C) (II) and (IV) (D) (III) and (IV)

ISOMERISM [7]
Q.49 The R/S configuration of these compounds are respectively.
HO H
CF3 H NH2 H CH3
HS CHO
COOH

(A) R,R,R (B) R,S,R (C) R,S,S (D) S,S,S

O
OD / D2O
Q.50 Ph (P) final product is ?
(prolonged)

O D O D
C
(A) Ph CD3 (B) Ph CH3
D D

O H O
(C) Ph CD3 (D)
Ph CH3
D

ISOMERISM [8]
 EXERCISE-II
Q.1 Which of the following molecules is/are identical with that represented by

(A) (B) (C) (D)

Q.2 The IUPAC name of the compound :

(A) (2E, 4E, 6Z)-octa-2,4,6-triene (B) (2E, 4E, 6E)-octa-2,4,6-triene

(C) (2Z, 4E, 6Z)-octa-2,4,6-triene (D) (2Z, 4Z, 6Z)-octa-2,4,6-triene

Q.3 Which of the following have zero dipole moment?

(A) p-Dichlorobenzene (B) Benzene-1, 4-diol
(C) Fumaric acid (D) Maleic acid

Q.4 Which of the following will show optical isomerism as well as geometrical isomerism.

(A) (B) (C) (D)

Q.5 Which of the following statements is/are not correct?

(A) Metamerism belongs to the category of structural isomerism
(B) Tautomeric structures are the resonating structures of a molecule
(C) Keto form is always more stable than the enol form
(D) Geometrical isomerism is shown only by alkenes

Q.6 Which of the following statements is/are correct?

(A) A meso compound has chiral centres but exhibits no optical activity
(B) A meso compound has no chiral centres and thus are optically inactive.
(C) A meso compound has molecules which are superimposable on their mirror images even though they
contain chiral centres
(D) A meso compound is optically inactive because the rotation caused by any molecule is cancelled by
an equal and opposite rotation caused by another molecule that is the mirror image of the first.

Q.7 Which of the following statements is/are not correct for D-(+) glyceraldehyde?
(A) The symbol D indicates the dextrorotatory nature of the compound
(B) The sign (+) indicates the dextrorotatory nature of the compound
(C) The symbol D indicates that hydrogen atom lies left to the chiral centre in the Fischer projection
diagram
(D) The symbol D indicates that hydrogen atom lies right to the chiral centre in the Fischer projection
diagram
ISOMERISM [9]
Q.8 Select the optically inactive compound among the following :

NH H3C COOH
(A) HN (B) H3C COOH

H3C CH3 HN NH
(C) HOOC COOH (D) OC CO

Q.9 The S-ibuprofen is responsible for its pain reliveing property. Which one of the structure shown is
S-ibuprofen.
O
Me C–OH
Me C Me H
(A) (B)
CH3 Me C
H C – OH
CH3 O
CH3 O
Me ||
Me C – OH
Me C H
(C) (D) Me C H
C – OH
O CH3

Q.10 Which of the following operations on the Fischer formula does not change its absolute

configuration?
(A) Exchanging groups across the horizontal bond
(B) Exchanging groups across the vertical bond
(C) Exchanging groups across the horizontal bond and also across the vertical bond
(D) Exchanging a vertical and horizontal group

Q.11 Which of the following statements for a meso compound is/are correct?
(A) The meso compound has either a plane or centre of symmetry
(B) The meso compound has at least one pair of similar stereocenters
(C) The meso compound is achiral
(D) The meso compound is formed when equal amounts of two enantiomers are mixed

Q.12 Which of the following states are correct:

(A) Any chiral compound with a single asymmetric carbon must have a positive optical rotation if the
compound has the R configuration
(B) If a structure has no plane of symmetry it is chiral
(C) All asymmetric carbons are stereocentres.
(D) Alcohol and ether are functional iosmers
ISOMERISM [10]
Q.13 Which of the following pairs of compound is/are identical?

(A) (B)

(C) (D)

Q.14 Which of the following compounds are optically active?

(A) CH3.CHOH.CH2.CH3 (B) H2C=CH.CH2.CH=CH2
HOOC NO2

(C) (D)
NO2 COOH

Q.15 Which of the following pairs can be resolved?

(A) (B)

(C) (D)

Q.16 Which of the following are correct representation of L–amino acids

(A) (B)

(C) (D)

ISOMERISM [11]
Q.17 Which of the following are D sugars:

(A) (B) (C) (D)

Q.18 Which out the following are Non-resolvable.

(A) (B) (C) (D)

Q.19 Which out of the following are resolvable.

H
H
(A) COOH (B) (C) (D)
COOH

Q.20 Concider the following structure and pick by the right statement :
H O
NH2 C
F OH
C C
H CH2OCH3
H CH2OCH3
CH3 OH III
I II
(A) I and II have R-configuration (B) I and III have R-configuration
(C) only III has S-configuration (D) I and III have S-configuration

Q.21 Which of the following is a 'threo' isomer?

CHO CH3 COOH
COOH
H OH Br H H Cl
NH2
(A) H OH (B) H OH (C) H OH (D) H
H OH
CH2OH CH3 CH3
CH3

Q.22 Which compound show tautomerism:

O
OH N OH

(A) (B) (C) (D) None of these

N=O

ISOMERISM [12]
Q.23 Which of the following compounds have higher enolic content than Keto content:
O O O
|| || O
(A) CH 3  C  C  CH 3 (B)

O O
O
(C) (D)

Q.24 Tautomer of following compound is :

O O

C – CH2 – C

(A) C – CH = C (B) C – CH2 – C

O OH OH O

(C) C – CH = C (D) C – CH2 – C

OH OH O OH

Q.25 Which of the following can tautomerise.

O O O

(A) CD3  C  Ph (B) (C) (D)

|| N
O H
Q.26 Identify the position isomer.

(A) & (B) &

CN NC
CN NC
O

(C) & (D)

OCH3 O
OCH3

Q.27 Enolic form of acetyl acetone is stabilised due to :

(A) resonance as a result of conjugation (B) intramolecular hydrogen bonding
(C) van der waals force (D) dipole-dipole repulsion

ISOMERISM [13]
Q.28 What is relation between (I), (II) and (III) ?
O OH O–
+ +
HN NH N N HN NH
(I) (II) (III)
– +
O N O HO OH O N O–
H N
H
(A) I and II are tautomers (B) III is conjugate base of II
(C) III is resonance structure of I (D) no relation exists

Q.29 An organic compound with molecular formula C2H5NO contains doubly linked atoms. It shows:
(A) chain isomerism (B) geometrical isomerism
(C) tautomerism (D) positional isomerism

Q.30 Select the correct statement.

Me
Me Me
Me Me Me N
H H H H T
H H H D
(P) (Q) (R) (S)
(A) All are optical isomer (B) Q,R,S are chiral molecules
(C) Only Q& R are resolvable (D) All contain chiral centres

Paragraph for Question Nos. 31 to 33

S(+) Mono Sodium Glutamate (MSG) is a flavour enhancer used in many foods. Fast foods often
contain substantial amount of MSG and is widely used in Chinese food. If one mole of above MSG was
placed in 845 ml solution and passed through 200 mm tube, the observed rotation was found to be
+ 9.6°.
+
COO¯Na
¯OOC—CH2—CH2—C

NH3 H

MSG
Q.31 Find out the specific rotation of (–) MSG:
(A) + 24° (B) + 56.8° (C) – 48° (D) None of these

Q.32 Find out the approximate percentage composition of (–) MSG in a mixture containing (+) MSG and
(–) MSG whose specific optical rotation is –20°.
(A) 83.3 % (B) 16.7 % (C) 91.6 % (D) 74 %

Q.33 If 33.8 g of (+) MSG was put in 338 ml solution and was mixed with 16.9 g of (–) MSG put in 169 ml
solution and the final solution was passed through 400 mm tube. Find out observed rotation of the final
solution .
(A) + 1.6° (B) + 4.8° (C) + 3.2° (D) None of these

ISOMERISM [14]
Q.34 Match the Column:
Column I Column II
Compound Number of optically active isomer
(A) Unsymmetrical compound with ‘n’ chiral carbon (P) 2n–1
(B) Symmetrical molecule with ‘n’ chiral carbon when n is even (Q) 2n–1 – 2n–1/2
(C) Symmetrical molecule with ‘n’ chiral carbon when n is odd (R) 2n

Q.35 Column-I Column-II

CH3 H
H CH2OH H3C CH2NH2
(A) and (P) Structural
NH2 OH
CH3 Cl
H Cl H CH3
(B) and (Q) Identical
Et Et
CH3 H
H H3C Et
OH
(C) and (R) Enantiomers
Et OH
H3C2 H3C2
(D) and (S) Diastereomers
OH H H OH

Q.36 Match List-I, List-II & List-III :

List-I List-II List-III
CH3 H
CH3
Br H
(a) HO H (1) HO C–C H (i) (2R, 3R)
CH3 CH3 Br

CH3 H
CH3
HO H
(b) Br H (2) Br C–C OH (ii) (2S,3S)
CH3 H CH3

CH3 H
CH3
H OH
C–C
(c) Br H (3) HO Br (iii) (2S,3R)
CH3
CH3 H

CH3 H
CH3
HO H
(d) H Br (4) Br C–C OH (iv) (2R, 3S)
CH3
CH3 H

ISOMERISM [15]
Q.37 Column I Column II
O O
|| ||
(A) CH 3  C  O  C3H 7 & Et  C  O  Et (P) Enantiomer

(B) & (Q) Positional isomers

(C) & (R) Metamers

(D) & (S) Tautomers

Q.38 Match the Column :

Column I Column II
COOH COOH
H OH H OH
;
(a) A pair of metamer (i) HO H H OH
COOH COOH
(b) tautomerism (ii) CH3OC3H7 ; C2H5OC2H5
CH3 CH3
H OH ; HO H
(c) A pair of geometrical isomer (iii)
COOH COOH
CH3 CH3 H3 C H
(d) A pair of distereomers (iv) C=C ; C=C
H H H CH3
O
||
(e) A pair of optical isomer (v) CH 3CH 2CH 2CH ; CH3CH2CH=CH–OH

ISOMERISM [16]
Q.39 Match the column :
Column I Column II
O OH

(A) (P) Tautomers

O OH

(B) (Q) Structural isomers

OH OH

(C) (R) Position isomers

O CH2

(D) (S) Atleast one of the two structures is enol

OH

Q.40 Column I Column II

(A) (P) Optical isomerism

(B) CH3–CH=C=CH–CH=CH–CH3 (Q) Geometrical isomerism

(C) (R) Positional isomerism

tBu H
Me
C=C
(D) (S) C. isomerism
Me
Me

ISOMERISM [17]
 EXERCISE-III
Q.1 How many benzenoid isomer are possible for cresol.

Q.2 Calculate the total number of stereoisomers in the following compounds.

(I) (II) (III)

Q.3 Find out the total number of cyclic isomers of C6H12 which are optically active?

Q.4 How many pair(s) of geometrical isomers are possible with C6H12 (only in open chain structures)

Q.5 Calculate the number of Benzenoid isomers possible for C6H3ClBrI.

Q.6 Calculate the total number of structural isomers of 3°-amines for the molecular formula C6H15N are?

Q.7 Calculate the number of chiral center in the molecule Ethyl 2,2-dibromo-4-ethyl-6-methoxy cyclohexane
carboxylate.

Q.8 How many monochlorinated products of methyl cyclohexane are optically active.

Q.9 How many cyclopentane structures (including stereo) are possible for C7H14.

2H2
Q.10 X 
Pt

Find out structures of X.

Q.11 How many enantiomers are possible on monochlorination of isopentane.

Q.12(a) Calculate the total number of cyclic isomeric carbonyl compounds of molecular formula C5H8O which
can't show geometrical isomerism. (Excluding enantiomers)

(b) Calculate the total number of open chain isomeric carbonyl compounds of molecular formula C5H8O
which can't show geometrical isomerism.

Q.13 Calculate the total number of chiral carbon atoms in.

Q.14 (a) The number of diastereoisomers (excluding optical) for 1-bromo-2-chloro-3-iodocyclopropane

(b) Minimum number of carbon atoms required for an alkane to show any kind of isomerism.

ISOMERISM [18]
Q.15 Assign E & Z configuration?
O O
O
O
(I) (II)
O
Z E
CH2CH2CH3
Ph
(III) CH – CH3 (IV) Cl
|
CH3
F
| NC CH = CH2
C–C–C Br
(V) F (VI)
HOOC CHO
C–C–C Cl
Z

C  CH O
HO
CH3 O O

(VII) OHC C – CH3

|
(VIII) O
O
CH3 O
18
Me OMe OH
H
(IX) (X) 16
Et O¯ Li
+
D OH

CH3
|
CH – CH2 – CH3
Me F
C  CH
(XI) (XII)
Cl Me CH3
H
Q.16 Write the structure of:
(i) (E) penta-1,3-diene (ii) (2Z, 4E)hexa-2,4-diene (iii) (2E, 4E)-3-ethylhexa-2,4-diene
(iv) (R)-2-Bromopentane (v) (S)-3-bromo-3-chlorohexane (vi) (2S, 3R)-2,3-dibromobutane
Q.17 In what stereoisomeric forms would you expect the following compounds to exist?

(a) EtCH(CO2H)Me (b) MeCH(CO2Et)CO2H (c)

(d) (e) (f) Et(Me)C=C=C(Me)Et

(g) (h) (i)

(j) (k)

ISOMERISM [19]
Q.18 What are the relationships between the following pairs of isomers?

(a) and (b) and

(c) and

(d) and

(e) and (f) and

(g) and (h) and

(i) and

Q.19 Mention the specific type of isomerism exhibited by each of the following pairs:
(a) 1,2-dichloro ethane and 1,1-dichloro ethane
(b) Propanoic acid and methyl acetate
(c) Methyl acetate and ethyl formate
(d) o-Nitrophenol and P-nitrophenol
(e) Anisole and o-cresol
(f) Phenol and Cyclohexa-2,4-dien-1-one

Q.20 With reasons, state whether each of the following compounds I to IX is chiral.

(I) (II) (III)

HO 2C CO 2H

(IV) (V) (VI) (VII)

ISOMERISM [20]
Q.21 Draw the two chair conformers of each compound and indicate which conformer is more stable.
(a) cis-1-ethyl-3-methylcyclohexane (b) trans-1-ethyl-2-isopropylcyclohexane
(c) trans-1-ethyl-2-methylcyclohexane (d) trans-1-ethyl-3-methylcyclohexane
(e) cis-1-ethyl-3- isopropylcyclohexane (f) cis-1-ethyl-4-isopropylcyclohexane

Q.22 Draw the most stable conformer of N-methylpiperidine.

Q.23 Considering rotation about the C-3 – C-4 bond of 2-methylhexane:

(a) Draw the Newman projection of the most stable conformer.
(b) Draw the Newman projection of the least stable conformer.

Q.24 Determine whether each of the following compounds is a cis isomer or a trans isomer.

(a) (b)

(c) (d)

(e) (f)

Q.25 Comment on the relationship among the following compounds.

(I) (II) (III) (IV)

Q.26 Calculate the total number of geometrical isomers possible for

Cl
Cl Cl H CH = CH – CH3
(i) (ii) (iii) C=C=C
Cl CH = CH – CH3
Cl Cl
Cl

ISOMERISM [21]
Q.27 Total number of streoisomers for the following molecule : (including optical)

(i) CH3 – CH – CH = CH CH = CH – CH – CH3 (ii)

| | Me
Cl CH3 COOH

NH2
N O
O N

(iii) EtO – P N N (iv)

OH
OEt

OH

(v) (vi)
O

Q.28 How many stereocenter and pseudochirality center present in the following compound?

O O
H2N NH2
O O

Q.29 A 0.1 M solution of an enantiomerically pure chiral compound. D has an observed rotation of +0.20° in
a 1 dm sample container, the molecular mass of the compound is 150.
(a) What is the specific rotation of D ?
(b) What is the observed rotation if this solution of D is diluted with an equal volume of solvent?
(c) What is the observed rotation if this solution is mixed with an equal volume of a solution that is 0.1 M in
L, the enantiomer of D?
(d) What is the specific rotation of D after the dilution described in part (b) ?
(e) What is the specific rotation of L, the enantiomer of D, after the dilution described in part (b)?
(f) What is the observed rotation of 10 ml of a solution that contains 0.01 mole of D and 0.005 mole of L?
(Assume a 1 dm path length)

ISOMERISM [22]
Q.30 Assign the priority order number to the following atoms or groups.
(a) –CHO, –CH2OH, –CH3 , –OH
(b) –Ph, –CH(Me)2, –H, –NH2
(c) –COOH, –Ph , –CHO, –CH = CH2
(d) –CH(Me)2, –CH=CH2, –CCH, –Ph
(e) –CH3, –CH2Br, –CH2OH, –CH3Cl
(f) –H, –N (Me)2, –Me, –OMe
(g) –CH = CH2, –Me, – Ph, –Et
(h) –CH2–CH2–Br, –Cl, –CH2–CH2–CH2–Br, (Me)2CH–
(i) –Cl, –Br, –I, –NH2
(j) NH2 , NO2 , CH2NH2 , CN

Q.31 Calculate the number of Benzenoid isomers possible for C6H3ClBrI.

Q.32 Decreasing order of enol content of the following. (along with proper explanation).

(a) (b) (c) (d)

(e)

Q.33 Ph  CH  CHO
|
OH
(A )
(A), (B) and (C) are structural isomers and isomerization is effectively carried out by trace of base. Give
structure of (B) and (C) and also write base catalysed mechanism for this interconversion.

ISOMERISM [23]
 EXERCISE-IV (A)
Q.1 True or False:
m-chlorobromobenzene is an isomer of m-bromochlorobenzene. [JEE 1985]

Q.2 Only two isomeric monochloro derivatives are possible for: [JEE 1986]
(A) n-butane (B) 2, 4-dimethylpentane
(C) benzene (D) 2-methylpropane

Q.3 True or False:

2, 3, 4-Trichloropentane has three asymmetric carbon atoms. [JEE 1990]

Q.4 Isomers which can be interconverted through rotation around a single bond are [JEE 1992]
(A) Conformers (B) Diastereomers (C) Enantiomers (D) Positional isomers

Q.5 The optically active tartaric acid is named as D–(+)–tartaric acid because it has a positive
(A) optical rotation and is derived from D-glucose
(B) pH in organic solvent
(C) optical rotation and is derived from D–(+)–glyceraldehyde
(D) optical rotation only when substituted by deuterium [JEE 1992]

Q.6 The shows: [JEE 1995(Scr.)]

(A) geometrical isomerism (B) optical isomerism

(C) geometrical & optical isomerism (D) tautomerism

Q.7 How many optically active stereoisomers are possible for butane-2,3-diol? [JEE 1997]
(A) 1 (B) 2 (C) 3 (D) 4

Q.8 The number of possible enantiomeric pairs that can be produced during monochlorination of 2-methyl
butane is [JEE 1997]
(A) 2 (B) 3 (C) 4 (D) 1

Q.9 When cyclohexane is poured on water, it floats, because: [JEE 1997]

(A) cyclohexane is in 'boat' form (B) cyclohexane is in 'chair' form
(C) cyclohexane is in 'crown' form (D) cyclohexane is less dense than water

Q.10 Which of the following compounds will show geometrical isomerism? [JEE 1998]
(A) 2-butene (B) propene (C) 1-phenylpropene (D) 2-methyl-2-butene

Q.11 Which of the following compounds will exhibit geometrical isomerism? [JEE 2000 (Scr.)]
(A)1-Phenyl-2-butene (B)3-Phenyl-1-butene (C)2-Phenyl-1-butene (D)1,1-Diphenyl-1-propene

ISOMERISM [24]
Q.12 The number of isomers for the compound with molecular formula C2BrClFI is
(A) 3 (B) 4 (C) 5 (D) 6 [JEE 2001 (Scr.)]

Q.13 Which of the following compounds exhibits stereoisomerism? [JEE 2002 (Scr.)]
(A) 2-methylbutene-1 (B) 3-methylbutyne-1
(C) 3-methylbutanoic acid (D) 2-methylbutanoic acid

Q.14 In the given conformation, if C2 is rotated about C2–C3 bond anticlockwise by an angle of 120° then
the conformation obtained is [JEE 2004 (Scr.)]

(A) fully eclisped conformation (B) partially eclipsed conformation

(C) gauche conformation (D) staggered conformation

Q.15 On monochlorination of 2-methylbutane, the total number of chiral compounds formed is

(A) 2 (B) 4 (C) 6 (D) 8 [JEE 2004]

Q.16 The number of structural isomers for C6H14 is [JEE 2007]

(A) 3 (B) 4 (C) 5 (D) 6

Q.17 Statement-1 : Molecules that are not superimposable on their mirror images are chiral.
because
Statement-2 : All chiral molecules have chiral centres.
(A) Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.
(B) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1.
(C) Statement-1 is True, Statement-2 is False.
(D) Statement-1 is False, Statement-2 is True. [JEE 2007]

Q.18 The correct statement(s) about the compound given below is (are) [JEE 2008]
Cl H
CH3
H3C

Cl H
(A) The compound is optically active
(B) The compound possesses centre of symmetry
(C) The compound possesses plane of symmetry
(D) The compound possesses axis of symmetry

ISOMERISM [25]
Q.19 The correct statement(s) concerning the structures E, F and G is (are) [JEE 2008]

H3C O H3C OH H3C CH3

H3C CH3 H3C CH3 H3C OH

(E) (F) (G)
(A) E, F and G are resonance structures (B) E, F and E, G are tautomers
(C) F and G are geometrical isomers (D) F and G are diastereomers

Q.20 The correct statement(s) about the compound H3C(HO) HC – CH = CH – CH (OH) CH3 (X) is (are)
(A) The total number of stereoisomers possible for X is 6
(B) The total number of diastereomers possible for X is 3
(C) If the stereochemistry about the double bond in X is trans, the number of enantiomers possible for X
is 4
(D) If the stereochemistry about the double bond in X is cis, the number of enantiomers possible for X
is 2 [JEE 2009]

Q.21 The bond energy (in kcal mol–1) of a C–C single bond is approximately [JEE 2010]
(A) 1 (B) 10 (C) 100 (D) 1000

Q.22 In the Newman projection for 2,2-dimethylbutane [JEE 2010]

X
H 3C CH3

H H
Y
X and Y can respectively be
(A) H and H (B) H and C2H5 (C) C2H5 and H (D) CH3 and CH3

ISOMERISM [26]
 EXERCISE-IV (B)
Q.1 Write structural formulae for all the isomeric alcohols having the molecular formula C4H10O.
[JEE 1984]

Q.2 Identify the pairs of enantiomers and diastereomers from the following compounds I, II and III.
[JEE 2000]

Q.3 (i) obs =  i x i

i
where i is the dipole moment of a stable conformer of the molecule, Z–CH2–CH2–Z and
xi is the mole fraction of the stable conformer.
Given : obs = 1.0 D and x (Anti) = 0.82
Draw all the stable conformers of Z–CH2–CH2–Z and calculate the value of (Gauche).
(ii) Draw the stable conformer of Y–CHD–CHD–Y(meso form), when Y= CH3 (rotation
about C2–C3) and Y = OH (rotation about C1 – C2 ) in Newmann projection.
[JEE 2005]

Q.4 The total number of cyclic structural as well as stereo isomers possible for a compound with the molecular
formula C5H10 is [JEE 2009]

Q.5 The total number of cyclic isomers possible for a hydrocarbon with the molecular formula C4H6 is
[JEE 2010]

ISOMERISM [27]
 ANSWER KEY
EXERCISE-I
Q.1 C Q. 2 A Q.3 A Q.4 B Q.5 A Q.6 D Q.7 B

Q.8 C Q.9 C Q.10 D Q.11 C Q.12 C Q.13 C Q.14 C

Q.15 C Q.16 B Q.17 A Q.18 C Q.19 C Q.20 C Q.21 A

Q.22 B Q.23 D Q.24 C Q.25 A Q.26 B Q.27 A Q.28 A

Q.29 C Q.30 B Q.31 A Q.32 A Q.33 D Q.34 A Q.35 D

Q.36 C Q.37 C Q.38 B Q.39 B Q.40 (i) B (ii) C Q.41 A

Q.42 A Q.43 A Q.44 D Q.45 B Q.46 B Q.47 B Q.48 C

Q.49 A Q.50 C

EXERCISE-II
Q.1 A, D Q.2 C Q.3 A,C Q.4 A, C, D

Q.5 B, C, D Q.6 A, C Q.7 A, D Q.8 A, C, D

Q.9 D Q.10 C Q.11 B, C Q.12 C, D

Q.13 A Q.14 A, C, D Q.15 B, C, D Q.16 A, C, D

Q.17 A, C, D Q.18 A, C Q.19 D Q.20 A, C

Q.21 B Q.22 A, C Q.23 B, D Q.24 A, C, D

Q.25 A, B, C Q.26 B, C Q.27 A, B Q.28 A, C

Q.29 B, C Q.30 B, C Q.31 D Q.32 C

Q.33 C Q.34 (A) R , (B) P, (C) Q Q.35 (A) P , (B) R , (C) Q , (D) R

Q.36 (a-4-iii) ; (b-3-iv) ; (c-2-ii) ; (d-1-i) Q.37 (A) R, (B) Q, (C) S, (D) P

Q.38 (a) ii (b) v (c) iv (d) i, iv (e) i, iii] Q.39 (A) P,Q,S; (B) Q,S; (C) Q,R,S; (D) Q,S

Q.40 (A) P,Q,R,S (B) P,Q,R,S (C) P,Q,R,S (D) P,Q,R,S

ISOMERISM [28]
 EXERCISE-III
Q.1 5 Q.2 (I) 4, (II) 3, (III) 4 Q.3 8 Q.4 4

Q.5 10 Q.6 7 Q.7 3 Q.8 8 Q.9 8

Q.10 7 Q.11 4 Q.12(a) 9 (b) 8 Q.13 (i) 6, (ii) 8

Q.14(a) 4 (b) 4 Q.15 Z – I, II, III, VI, VII ; E – IV, V, VIII, IX, X, XI, XII

Q.16 (i) (ii)

Me
Pr
C2H5
H Br
(iii) (iv)
CH3

C3H7 CH3
H Br
Br Cl
(v) (vi) H Br ]
C2H5 CH3

Q.17 Optical : a,b,c,d,f,g,i,j,k ; Geometrical isomer : c,g,j ; None : e,h,

Q.18 (a) Enantiomers, (b) Enantiomers, (c) Geometrical isomers & Diastereomers, (d) Positional,
(e) Optical (Diastereomers), (f) Diastereomers, (g) Enantiomers, (h) Identical, (i) Geometrical isomers
(Diastereomers)

Q.19 (a) Positional (b) Functional (c) Metamerism (d) Positional (e) Functional (f) Tautomerim

Q.20 achiral : I, III, IV ; chiral : II,V, VI, VII

Q.21 Stable are : (a) diequatorial, (b) , (c) (d) ,

(e) , (f)

ISOMERISM [29]
Q.22

H H Et

Q.23 (a) (b) ]

H H
H H H
Et H

Q.24 (a) cis (b) cis (c) cis (d) trans (e) trans (f) trans

Q.25 II, III & IV are Identical; I is Enantiomer of these.

Q.26 (i) 16 (ii) 9 (iii) 4

Q.27 (i) 26 , (ii) 24 , (iii) 2 , (iv) 4 , (v) 3, (vi) 8

Q.28 3,1

Q.29 (a) + 13.3 ; (b) 0.10 ; (c) zero ; (d) unchanged ; (e) unchanged ; (f) 1

Q.30 (a) 4,1,2,3 (b) 4,1,2,3 (c) 1,3,2,4 (d) 4,3,2,1 (e) 2,4,3,1 (f) 4,2,3,1 (g) 3,1,4,2 (h) 2,4,1,3
(i) 3,2,1,4 (j) 2, 1, 4, 3

Q.31 10

Q.32 > > > >

(a) (b) (c) (d) (e)

(b) Active 'H' atom / Acidic 'H' atom so has more enolic content (enol stabilise by resonance & Intra
molecular H–bonding) >
(c) Enolic contents decreases with introduction of e– donator group which causes repulsion in enolic form .

(d) Due to ester group acidic structure of active H decreases & C=C of enol undergoese cross resosnace >

(e) Lowest enolic content because is more stable than Bond

Q.33
[Sol. Ph  C  CH Ph  C  CH 2
| | || |
OH OH O OH
(B) (C )

ISOMERISM [30]
 (Mechanism)

Ph  CH  CH 
 Ph  C  CH Ph  C  CH
| || | | | |
OH O OH O  OH OH
(B)


Ph  C  CH 2 Ph  C  CH
|| | || | ]
O OH O OH
( C)

EXERCISE-IV (A)
Q.1 False Q.2 D Q.3 True Q.4 A Q.5 C

Q.6 B Q.7 B Q.8 A Q.9 D Q.10 A, C

Q.11 A Q.12 D Q.13 D Q.14 C Q.15 B

Q.16 C Q.17 C Q.18 A, D Q.19 B, C, D Q.20 A, D

Q.21 C Q.22 B, D

EXERCISE-IV (B)
Q.1 4 Q.2 enantiomers–I & III; diastereomers – I & II and II & III
1
Q.3 (i) D, (ii) Anti form when Y=CH3 & Gauche when Y = – OH
0.18

Q.4 7 Q.5 5

ISOMERISM [31]