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What is Isomerism?

Compounds having the same molecular formula but different properties are known as isomers and this phenomenon is known as isomerism. 

The term "isomer" comes from the Greek words "isos" and "meros," which together mean "equal parts." A Swedish chemist named Jacob Berzelius created this term in 1830.

Classification of Isomerism

Two common types of isomerism are structural isomerism and stereoisomerism. 

  1. Structural Isomerism: In structural isomerism, molecules with identical molecular formulas have different arrangements of atoms. This can manifest as variations in the branching of carbon chains, positions of functional groups, or the presence of different functional groups.
  2. Stereoisomerism: Stereoisomerism, on the other hand, involves molecules with the same connectivity of atoms but differ in their spatial arrangement. This can occur as geometric isomerism, where groups around a double bond have different spatial orientations, or optical isomerism, where molecules are mirror images of each other but cannot be superimposed. These isomers can exhibit unique properties due to their distinct spatial structures.

Classification of IsomerismClassification of Isomerism

What is Structural isomerism? 

  • Compounds having the same molecular formula and different connectivity of atoms (Structure is different) are called Structural Isomers.
  • A straightforward example is the alkane with a molecular formula of C4H10, showcasing structural isomers with varied arrangements. As the number of carbon atoms in the alkane molecule increases, the number of structural isomers also increases.

Structural Isomers of ButaneStructural Isomers of Butane

Question for Structural Isomerism
Try yourself:
Which of the following best describes structural isomerism?
View Solution

Classification of Structural Isomers

There are six types of Structural Isomers: 

  • Chain Isomers: These isomers have the same molecular formula but differ in the arrangement of the carbon skeleton, creating distinct chains or branches.
  • Position Isomers: In this type, atoms are attached at different positions on the carbon chain, leading to unique compounds with distinct physical and chemical properties.
  • Functional Group Isomers: Molecules with the same molecular formula but different functional groups fall under this category. For example, an alcohol and an ether can be functional group isomers.
  • Tautomers: Tautomeric isomers exist in equilibrium with each other due to the migration of a hydrogen atom or a proton. They rapidly interconvert, creating dynamic structures.
  • Metamers: Metamers have the same alkyl groups on either side of a functional group, such as an ether or a secondary amine, but with a different arrangement of alkyl groups.
  • Ring Isomers: These isomers involve variations in the arrangement of atoms to form different cyclic structures while maintaining the same molecular formula. The shift from one ring structure to another characterizes this type of isomerism.


Classification of Structural IsomersClassification of Structural Isomers

Chain Isomerism

Compounds having the same molecular formula but differ in the length of the principal chain.

Structural Isomerism | Chemistry Class 11 - NEET

How to Form Chain Isomers?

CnH2n+2Structural Isomerism | Chemistry Class 11 - NEET CnH2n+1

Alkane                   Alkyl group

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

dark line (-) represents vacant valency where any group can be attached.

- Iso-GroupStructural Isomerism | Chemistry Class 11 - NEET
e.g.Isoheptane

Structural Isomerism | Chemistry Class 11 - NEET

e.g. Isooctane (exception for the Iso group)

Structural Isomerism | Chemistry Class 11 - NEET

- Neo Group 

Structural Isomerism | Chemistry Class 11 - NEET

To prepare the neo compound firstly the above groupStructural Isomerism | Chemistry Class 11 - NEET  is written. After that required no. of carbon is added in the straight chain.

e.g. neopentane

Structural Isomerism | Chemistry Class 11 - NEET

e.g. neo heptane

Structural Isomerism | Chemistry Class 11 - NEET

Examples of Chain Isomerism:

1. C4H10 has 4 forms

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

2. C5H12 has it's three forms:

C - C - C - C - C  
(n-pentane)

Structural Isomerism | Chemistry Class 11 - NEET

Consider n-pentane:

Structural Isomerism | Chemistry Class 11 - NEET

= 3 form 

Consider Isopentane,

Structural Isomerism | Chemistry Class 11 - NEET

Consider neopentane,

Structural Isomerism | Chemistry Class 11 - NEET

= only one form.

Total forms of C5H11 - = 8

3. CH3 - CH2 - CH2 - CH3   - butane (n-butane)

and

Structural Isomerism | Chemistry Class 11 - NEET - 2-methylpropane (Isobutane)

 

4. Structural Isomerism | Chemistry Class 11 - NEET - butanoic acid and

Structural Isomerism | Chemistry Class 11 - NEET - 2-methyl propanoic acid

 

Ex.1 Find all the structural isomers of C6H14 

Sol. 

Structural Isomers of C6H14Structural Isomers of C6H14

 

Position Isomerism

Compounds having the same molecular formula and same principal chain but differ in the position of functional group, multiple bonds, and substitution group are known as position isomers.

Position IsomerismPosition Isomerism

e.g. C - C - C = C (1-butene)  and C - C = C - C ( 2-butene)

e.g. Structural Isomerism | Chemistry Class 11 - NEET (1-chloropropane)  and Structural Isomerism | Chemistry Class 11 - NEET (2-chloropropane)  are position isomers.

 

e.g. Structural Isomerism | Chemistry Class 11 - NEET (1-propanol)  and Structural Isomerism | Chemistry Class 11 - NEET (2-propanol)

 

Note: Structural Isomerism | Chemistry Class 11 - NEET and Structural Isomerism | Chemistry Class 11 - NEET are chain isomers, not position isomers.

The above example can be best understood taking the following example

C - C - C - C and Structural Isomerism | Chemistry Class 11 - NEET

In this, the last carbon has been placed to IInd position to form chain isomer the same has happened with above example and hence they are chain isomer to each other.

Question for Structural Isomerism
Try yourself:
Which of the following compounds is an example of chain isomerism?
View Solution
 

Ex.2 Find the relation between the given compounds:

(A) C - C - C - C - C - C

 

(B)Structural Isomerism | Chemistry Class 11 - NEET

 

(C) Structural Isomerism | Chemistry Class 11 - NEET

 

(D) Structural Isomerism | Chemistry Class 11 - NEET

 

(E) Structural Isomerism | Chemistry Class 11 - NEET

Sol. a, b →chain isomers. b, c →position isomers.

c, d →chain isomers. d, e →position isomers.

Ex.3 How many monochloro derivatives will be of C4H10 (Only structural) 

Sol.Structural Isomerism | Chemistry Class 11 - NEET

Monochloro Derivative of C4H10Monochloro Derivative of C4H10

Important: Monochlorination →Replace one H by Cl

Ex.4 An alkane having molecular formula C5H12 can give only one product on monochlorination. Find the IUPAC name of the alkane. 

Sol.Structural Isomerism | Chemistry Class 11 - NEET

(2, 2-dimethyl pentane)

Ex.5Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET Mono chlorinated products (Excluding Stereoisomers)? 

 

Sol.Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

Ex.6 Find the total structural isomer of C5H10

Sol. To solve these kinds of problems we should at once draw all possible structures of corresponding alkanes and then we should check how many possibilities are there to put a double bond.

Structural Isomerism | Chemistry Class 11 - NEET = 2

Structural Isomerism | Chemistry Class 11 - NEET = 3

Structural Isomerism | Chemistry Class 11 - NEET no double bond can be placed in this compound as the valency of C will exceed from 4

Total open chain structural isomers = 5

* To form a cyclic structure we should always start with 3 carbon ring.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

total structural isomers = 5 + 5 = 10

Ex.7 Find the total structural isomers of C4H6

Sol. Total unsaturation of C4H6 = 2

i.e. possibility = one triple bond, or 2 double bonds, or (one ring + one double bond)

Structural Isomerism | Chemistry Class 11 - NEET ( indicates the possible position of triple bond)

Structural Isomerism | Chemistry Class 11 - NEET → (No triple bond)

for alkene,

Structural Isomerism | Chemistry Class 11 - NEET

total open chain = 2 + 2 = 4

for cyclic Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

total structural isomers (cyclic, acyclic) = 9

Ex.9 Find all the structural dichloro derivatives of cyclopentane. 

Sol.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

Total structural isomer = 3

Functional Group Isomerism

Compounds having same molecular formula but different in functional group are known as functional isomers.

Structural Isomerism | Chemistry Class 11 - NEET

Important:

  • Aldehyde, Ketone, cyclic ethers, cyclic alcohol, unsaturated alcohol etc. are functional isomers to each other.
  • Alcohol and ether are functional isomers to each other. e.g. CH3CH2OH, CH3OCH3
  • Acids and esters are functional isomers to each other. eg. Structural Isomerism | Chemistry Class 11 - NEET
  • Cyanide and Isocyanide are functional isomers to each other but HCN and HNC are tautomers to each other.
  • * 1°, 2° and 3° amine are functional isomers to each other.

e.g. C3H6O          CH3 - CH2 CHO    Structural Isomerism | Chemistry Class 11 - NEET    CH2 = CH - CH2OH      

Structural Isomerism | Chemistry Class 11 - NEET

Ex.10 How many primary, secondary, and tertiary alcohols are possible for C5H13O?(Only structural) 

Sol. For 1° alcohol (-CH2OH)

C5H12OH ⇒ C4H9 - CH2 - OH (4 form)

for 2° alcohol Structural Isomerism | Chemistry Class 11 - NEET → Structural Isomerism | Chemistry Class 11 - NEET  

Replace one C (1 form)

total = 3

for 3° alcohol  Structural Isomerism | Chemistry Class 11 - NEET

total = 4 + 3 + 1 = 8

or C5H13O ⇒ C5H12 - OH (8 form)

Ex.11 How many ethers are possible in C5H12O?(Only structural). 

Sol. C4H9OCH3   ⇒    C3H7OC2H5
        (4 form)            (2 form)

total = 6

Ex.12 How many 1º, 2º, and 3º amine are possible for C5H13N(Only structural). 

Sol. For 1º amine (- NH2)

C5H11 NH2 ⇒ (8 form) = 8

for 2º Amine, (- NH -) C4H9 - NH - CH ⇒ 4 forms

Also, C3H7 - NH - C2H5

(2 form)

total form at 2º = 4 + 2 = 6

for 3º Structural Isomerism | Chemistry Class 11 - NEET

C3H7 - Structural Isomerism | Chemistry Class 11 - NEET (2 form)

 

Also, Structural Isomerism | Chemistry Class 11 - NEET (1 form)

Total form of 3º = 2 + 1 = 3

Total no. of amines = 8 + 6 + 3 = 17

Ex.13 For molecular formula C4H9NO, how many amides will be there that will not form H-bond?(Only structural) 

Sol.Structural Isomerism | Chemistry Class 11 - NEET (1º amide) Structural Isomerism | Chemistry Class 11 - NEET (2º amide) Structural Isomerism | Chemistry Class 11 - NEET (3º amide)

for 1º amide

Structural Isomerism | Chemistry Class 11 - NEET (2 form)

for 2º amide, Structural Isomerism | Chemistry Class 11 - NEET (2 form) Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

total 2º amide = 4

for 3º amide

Structural Isomerism | Chemistry Class 11 - NEET      Structural Isomerism | Chemistry Class 11 - NEET

3º amide will not form H-bond hence there will be 2 amides which will not form H-bond.

Ex.14 Find all 1º, 2º and 3º amides for C3H7NO(Only structural) 

Sol. For 1º amides

Structural Isomerism | Chemistry Class 11 - NEET (1 form)   , total 1º amide = 1

for 2º amide

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET = 2 form

for 3º amide

Structural Isomerism | Chemistry Class 11 - NEET total 3º amide = 1

total amides (1º 2º 3º) = 1 + 2 + 1 = 4

Ex.15 Find the total no. of acid and esters from C4H8O2(Only structural) 

Sol. For acid, (- COOH)    C3H7 - COOH (2 form)

for ester, Structural Isomerism | Chemistry Class 11 - NEET → alcohol part

Structural Isomerism | Chemistry Class 11 - NEET   

CH3COOH C2H5OH

for ester, Structural Isomerism | Chemistry Class 11 - NEET (2 form) Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

total esters = 4

 

Ex.16 C4H4O4 may be (Only structural) 

(i) Saturated dicarboxylic acid (ii) Unsaturated dicarboxylic acid 

(iii) Cyclic diester (iv) Saturated di aldehyde 

Sol. Three unsaturation.

(ii) and (iii) is the Ans.

Structural Isomerism | Chemistry Class 11 - NEET and Structural Isomerism | Chemistry Class 11 - NEET

 

Ex.17 How many aromatic isomers will be possible for C7H8O(Only structural)

Sol.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

Total = 5

Ex.18 Find the possible dichloro derivatives of C6H4Cl(Only structural) 

Sol.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET


Ex.19 C6H4Cl2 →C6H3Cl(Only structural)

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEET

find the value of x, y, z.

Sol.

Structural Isomerism | Chemistry Class 11 - NEET

(1, 2, 4)

Two possibilities are there for placing Cl in place of H.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

y = 3 There is one possibility of placing Cl, therefore z = 1

x = 2, y = 3, z = 1

Ex.20 Find the total carbonyl compound (aldehydes and ketones) formed by C5H10O and also find the relation between carbonyl compounds that have the same no. of a-hydrogen.(Only structural) 

Sol. For ketones,

Structural Isomerism | Chemistry Class 11 - NEET  and   Structural Isomerism | Chemistry Class 11 - NEET

Isomerism - 

(2 form)

total ketones = 3

for aldehydes Structural Isomerism | Chemistry Class 11 - NEET   
                          (4 forms)

total aldehydes = 4

total carbonyl compounds = 4 + 3 = 7

CH3 - CH2 - CH2 - CH2 - CHO (2 α H) Structural Isomerism | Chemistry Class 11 - NEET (one α H)

 

Structural Isomerism | Chemistry Class 11 - NEET (2 α H) Structural Isomerism | Chemistry Class 11 - NEET (no α hydrogen)

 ketone, Structural Isomerism | Chemistry Class 11 - NEET (5 α H)

Structural Isomerism | Chemistry Class 11 - NEET

 

Ex.21 Find total acyclic structural isomer of C6H12 (Only structural) 

Sol.

(1) Structural Isomerism | Chemistry Class 11 - NEET = 3

 

(2) Structural Isomerism | Chemistry Class 11 - NEET = 4

 

(3) Structural Isomerism | Chemistry Class 11 - NEET = 1

 

(4) Structural Isomerism | Chemistry Class 11 - NEET = 2

 

(5) Structural Isomerism | Chemistry Class 11 - NEET = 3

total = 13 isomers.

 

Ex.22 Find the total conjugated diene in C5H(Only structural)

Structural Isomerism | Chemistry Class 11 - NEET →one possibility

Structural Isomerism | Chemistry Class 11 - NEET →one possibility

Structural Isomerism | Chemistry Class 11 - NEET no possibility of placing a double bond the valency of C will be more than four.

 

Ex.23 Find the total cumulated diene in C5H8. (Only structural) 

 

Sol.

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET →no form cumulated diene

total = 3

⇒ Isolated dienes,

C - C - C - C - C →Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET →no form isolated diene

total = 1

 Metamerism

  • Compounds having the same molecular formula but differ from the nature of the alkyl group directly attached to a polyvalent atom or polyvalent functional group.
  • This type of isomerism is found in those types of compounds that have polyvalent atoms or polyvalent functional groups, e.g. ether, 2º amine, ester, etc.Structural Isomerism | Chemistry Class 11 - NEET

Examples of metamers:

1.
Structural Isomerism | Chemistry Class 11 - NEET

 2.

(a)Structural Isomerism | Chemistry Class 11 - NEET

 

(b) CH3 - CH2 - CH2 - NH - CH2 - CH3

a & b are metamers.

Tautomerism

Compounds having the same molecular formula but different due to the oscillation of an atom (usually H ) are known as tautomers.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

as after removal of H+, the anion formed is resonance stabilized.

Keto-enol Tautomerism: 

Keto-Enol TautomerismKeto-Enol Tautomerism

Mechanism :

Structural Isomerism | Chemistry Class 11 - NEET                                                                 Structural Isomerism | Chemistry Class 11 - NEET

*OH- acts as a catalyst.

Base Catalysed Tautomerism :

 

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

Mechanism:

* enol is more acidic than keto.

* After removal of H+ from both form.

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEET .......(i)

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEET .......(ii)

In Ist -ve charge is on C and in IInd -ve charge is on O therefore (ii) is more stable than (i) hence enol form is more acidic than the keto form.

Acid Catalysed Tautomerism:

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

 

Ex.24

Structural Isomerism | Chemistry Class 11 - NEET  Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET
Structural Isomerism | Chemistry Class 11 - NEET
 

  • In the case of base-catalyzed tautomerism, the stability of carbanion is the deciding factor.
  • For acid-catalyzed tautomerism, the stability of the product will be the deciding factor.

Ex.25

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET P1 + P2

 

Sol.

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET+  Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET                             (major)               (minor)

(3 α H)Structural Isomerism | Chemistry Class 11 - NEET +     Structural Isomerism | Chemistry Class 11 - NEET (7 α H)

(minor)                            (major)

 

Ex.26 Write the enol form:

Structural Isomerism | Chemistry Class 11 - NEET 

 

Sol.

Structural Isomerism | Chemistry Class 11 - NEET

Generally keto form is more stable than enol but in some cases, the stability of enol form is greater than keto. This is due to

(i) Intramolecular H-bonding

(ii) Aromatic character

(iii) Extended conjugation

(iv) Steric factor

e.g. Structural Isomerism | Chemistry Class 11 - NEET

* Due to intramolecular H-bonding formation of 6-member ring takes place which is the cause of stability.

* This can be also summarized as:

Structural Isomerism | Chemistry Class 11 - NEET

If G = H % of enol 80 - 90%

G = Ph % of enol 90 - 99%

G = CH% of enol 70 - 80%

G = OC2H% of enol 5 - 10%

(one side)

Structural Isomerism | Chemistry Class 11 - NEET

* Cross conjugation restricts the Resonance.

Structural Isomerism | Chemistry Class 11 - NEET

Ex.27 Compare the enol percent.

(A) CH3CHO

(B) Structural Isomerism | Chemistry Class 11 - NEET

(C) Structural Isomerism | Chemistry Class 11 - NEET

(D) Structural Isomerism | Chemistry Class 11 - NEET

(E) Structural Isomerism | Chemistry Class 11 - NEET

(F) Structural Isomerism | Chemistry Class 11 - NEET

(G) Structural Isomerism | Chemistry Class 11 - NEET 

Sol. g > f > e > d > c > b > a

* In the case of a and b

After forming the enol form

CH2 = CH - OH (no ∝ H)

Structural Isomerism | Chemistry Class 11 - NEET more stable = higher %

* Structural Isomerism | Chemistry Class 11 - NEET

* Structural Isomerism | Chemistry Class 11 - NEET

* Structural Isomerism | Chemistry Class 11 - NEET enol % > keto %

* Structural Isomerism | Chemistry Class 11 - NEET (Keto < enol due to Intramolecular H-bond)

* Structural Isomerism | Chemistry Class 11 - NEET

keto > enol

Ex.28 Find the enol form of the given compound.

Structural Isomerism | Chemistry Class 11 - NEET

 

Sol.

Structural Isomerism | Chemistry Class 11 - NEET

* The above case is called para tautomerism. Here g-Hydrogen participate in tautomerism.

Ex.29 Compare the enol content

(A) Structural Isomerism | Chemistry Class 11 - NEET

(B) Structural Isomerism | Chemistry Class 11 - NEET

(C) Structural Isomerism | Chemistry Class 11 - NEET

(D) Structural Isomerism | Chemistry Class 11 - NEET

 

Sol. After removing H  (acidic-H) from the compounds

(A) Structural Isomerism | Chemistry Class 11 - NEET

(B) Structural Isomerism | Chemistry Class 11 - NEET

(C) Structural Isomerism | Chemistry Class 11 - NEET

(D) Structural Isomerism | Chemistry Class 11 - NEET

* Enol percent ∝ stability of carbanion

a > b > d > c

* Formation of carbanion is one of the steps from keto to enol. Therefore can be calculated as a percent of the stability of the carbanion.

Ex.30 Find the enol form of

Structural Isomerism | Chemistry Class 11 - NEET

Nitro and Acinitro form 

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

(acinitro)

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET (acinitro)

Structural Isomerism | Chemistry Class 11 - NEET 

* (CH3)3 C - NO2 will not show nitro and acinitro form it has no H w.r.t to the NO2 group.

Imine and Enamine 

Structural Isomerism | Chemistry Class 11 - NEET

For this type of tautomerism, there must a H w.r.t. (-CH = NH) group.

Amide and Amidol 

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

 

Nitroso and Oxime form 

Structural Isomerism | Chemistry Class 11 - NEET

II > I (stability)

due to extended conjugation in (II)

Hydrazone and Azoform 

NH2 NH2 (Hydrazine)

Structural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEET

CH3 - CH = N - NH - Ph Structural Isomerism | Chemistry Class 11 - NEET CH3 - CH2N = N - Ph

(extended conjugation)

Azo > Hydrazone (stability)

Ex.31 Compare enol percent.

(i) Structural Isomerism | Chemistry Class 11 - NEET

(ii) Structural Isomerism | Chemistry Class 11 - NEET

(iii) Structural Isomerism | Chemistry Class 11 - NEET

Sol. As we know C - D > C - H (Bond strength)

⇒ C - D will not break easily.

⇒ Compound will have less tendency to come into in enol form as C - D bond breaking is one of the step for conversion of keto into end.

⇒ enol percent will be less.

⇒ (i) > (ii) > (iii) (enol content)

Deuterium Exchange Reaction 

(Deuterium Exchange Tautomerism)

 

Structural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET →Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET (final product)

* To get the product directory replace all a-hydrogen w.r.t. carbonyl group by D(Deuterium):

e.g. Structural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEETStructural Isomerism | Chemistry Class 11 - NEET

 

Ring-chain Isomerism

Ring Chain IsomerismRing Chain IsomerismIf one isomer has an open chain structure and the other has cyclic structure then isomers are known as ring-chain isomers and isomerism between them is known as ring-chain isomerism.

For examples :

(i) Alkene and cycloalkane, (CnH2n)

CH3 - CH = CH2Structural Isomerism | Chemistry Class 11 - NEET

(ii) Alkyne and cycloalkene, (CnH2n - 2)

C4H6 : CH3 - CH2 - C º CH Structural Isomerism | Chemistry Class 11 - NEET

(iii) Alkenols and cyclic ethers, (CnH2nO)

C3H6O : CH2 = CH - CH2OH Structural Isomerism | Chemistry Class 11 - NEET

Note: Ring-chain isomers are always functional isomers.

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FAQs on Structural Isomerism - Chemistry Class 11 - NEET

1. What is isomerism?
Ans. Isomerism is a phenomenon in which two or more compounds have the same molecular formula but different structural arrangements or spatial orientations, resulting in different chemical and physical properties.
2. What is structural isomerism?
Ans. Structural isomerism is a type of isomerism in which compounds have the same molecular formula but differ in the connectivity of atoms within the molecule. It can be further classified into different types, such as chain isomerism, position isomerism, functional group isomerism, metamerism, tautomerism, and ring-chain isomerism.
3. What is chain isomerism?
Ans. Chain isomerism is a type of structural isomerism in which compounds have the same molecular formula but differ in the arrangement of carbon chain or backbone. This means that the carbon atoms are arranged in a different order in each isomer.
4. What is position isomerism?
Ans. Position isomerism is a type of structural isomerism in which compounds have the same molecular formula but differ in the position of a functional group or substituent within the molecule. This means that the functional group or substituent is attached to different carbon atoms in each isomer.
5. What is functional group isomerism?
Ans. Functional group isomerism is a type of structural isomerism in which compounds have the same molecular formula but differ in the functional group present in the molecule. This means that the compounds have different functional groups but the same number of carbon, hydrogen, and oxygen atoms.
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