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Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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Compounds having the same molecular formula (M.F.) but differ in their properties are known as isomers and this phenomenon is known as isomerism. 

Classification:

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural isomerism:

Compounds having the same M.F. and different in connectivity of atom (Structure is different).

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Chain Isomerism:

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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


e.g.1  CH3 - CH2 - CH2 - CH3   - butane (n - butane)

and

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

 

e.g.2 Structural Isomerism - Notes | Study Chemistry Class 11 - NEET - butanoic acid and

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET - 2-methylpropanoic acid

 

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET (iso group)
e.g. Isoheptane

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Isooctane (exception of Iso group)

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Neo group Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

e.g. neopentane

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

neoheptane

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Alkyl Group :

CnH2n+2Structural Isomerism - Notes | Study Chemistry Class 11 - NEET CnStructural Isomerism - Notes | Study Chemistry Class 11 - NEET

Alkane                   Alkyl group

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

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

 

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(Isopropyl alcohol)

Thus we can conclude that

C3H7 - → Two forms.

* C4H10

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* C5H12 has it's three forms:

C - C - C - C - C  
(n-pentane)

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Consider n-pentane:

 

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

= 3 form 

Consider Isopentane,

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Consider neopentane,

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

= only one form.

Total forms of C5H11 - = 8

Ex.1 Find all the structural isomers of C6H14 

Sol. 

C - C - C - C - C - C Structural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEET 

 

Position Isomerism


Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

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

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

 

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

 

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET and Structural Isomerism - Notes | Study 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 - Notes | Study 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.

 

Ex.2 Find the relation between the given compounds:

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

 

(B)Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(C) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(D) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(E) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

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

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

* Monochlorination →Replace one H by Cl

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

Sol.Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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 - Notes | Study Chemistry Class 11 - NEET

(2, 2-dimethyl pentane)

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

 

Sol.Structural Isomerism - Notes | Study Chemistry Class 11 - NEET 

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

Ex.6 Find the total structural isomer of C5H10. 

Sol. For solving 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 double bond.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET = 2

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET = 3

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

Total open chain structural isomers = 5

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study 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 bond or (one ring + one double bond)

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET (¯ indicate possible position of triple bond)

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET → {No triple bond}

for alkene,

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

total open chain = 2 + 2 = 4

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

total structural isomers (cyclic, acyclic) = 9

 

Ex.8 C3H8Structural Isomerism - Notes | Study Chemistry Class 11 - NEET ? (Only structural in all)

           Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Sol. For monochloroderivative,

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(1) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(2) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(3)

(4) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Total dichloroderivatives = 4

Trichloroderivative,

(1) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(2) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(3) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(4) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(5) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* To find di or trichloroderivative

We place two or three chlorine at last carbon and after that rotate one Cl by keeping the other two at the same the place.

Ex.9 Find all the structural dichloroderivative of cyclopentane. 

Sol.

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

Total structural isomer = 3

Functional Group Isomerism

 

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* 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 ester are functional isomers to each other.

eg. Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Cyanide and Isocyanide are functional isomer to each other but HCN and HNC are tautomers to each other.

* 1°, 2° and 3° amine are functional isomers to each other.

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

Sol. For 1° alcohol (-CH2OH)

C5H12OH ⇒ C4H9 - CH2 - OH (4 form)

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

Replace one C (1 form)

total = 3

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

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

 

Also, Structural Isomerism - Notes | Study 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 amide will be there which will not form H-bond ?(Only structural) 

 

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

for 1º amide

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

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

total 2º amide = 4

for 3º amide

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

for 2º amide

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

for 3º amide

Structural Isomerism - Notes | Study 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 - Notes | Study Chemistry Class 11 - NEET → alcohol part

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET   

CH3COOH C2H5OH

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

 

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

Sol.

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

Total = 5

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

Sol.

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


Ex.19 C6H4Cl2 →C6H3Cl(Only structural)

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

find the value of x, y, z.

Sol.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(1, 2, 4)

There are two possibilities placing Cl in place of H.

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

y = 3 There are one possibilities 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 which have same no. of a-hydrogen.(Only structural) 

Sol. For ketones,

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

Isomerism - 

(2 form)

total ketones = 3

for aldehydes Structural Isomerism - Notes | Study 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 - Notes | Study Chemistry Class 11 - NEET (one α H)

 

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

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

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

Sol.

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

 

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

 

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

 

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

 

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

total = 13 isomers.

 

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET →one possibility

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET →one possibility

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

 

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

 

Sol.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

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

total = 3

⇒ Isolated dienes,

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

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

total = 1

Metamerism

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

This type of isomerism is found in those types of compounds which have polyvalent atoms or polyvalent functional group, e.g. ether, 2º amine, ester etc.

Compound having same molecular formula but differ form the nature of alkyl group directly attached with polyvalent atom or polyvalent functional group.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

* (a)Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

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

a & b are metamers

Tautomerism

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

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

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

Keto-enol Tautomerism:

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET


Mechanism :

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

*OH- acts as catalyst.

Base Catalysed Tautomerism :

 

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

Mechanism →Structural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEET

* enol is more acidic than keto.

* After removal of H+ from both form.

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET →Structural Isomerism - Notes | Study 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 keto form.

Acid Catalysed Tautomerism:

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

 

Ex.24

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

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

* In case of base catalysed tautomerism the stability of carbanion is the deciding factor.
* For acid catalysed tautomerism the stability at the product will be the deciding factor.

Ex.25

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

 

Sol.

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

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

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

(minor)                            (major)

 

Ex.26 Write the enol form:

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET 

 

Sol.

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

* Cross conjugation restricts the Resonance.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET


Ex.27 Compare the enol percent.

(A) CH3CHO

(B) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(C) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(D) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(E) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(F) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(G) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET 

Sol. g > f > e > d > c > b > a

* Incase of a and b

After forming enol form

CH2 = CH - OH (no ∝ H)

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

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

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

* Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

keto > enol

Ex.28 Find the enol form the given compound.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

Sol.

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

Ex.29 Compare the enol content

(A) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(B) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(C) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(D) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

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

(A) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(B) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(C) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

(D) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

* Enol percent ∝ stability of carbanion

a > b > d > c

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


Ex.30 Find the enol form of

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Nitro and Acinitro form 

 

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

(acinitro)

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

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET 

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

Imine and Enamine

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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


Amide and Amidol

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

 

Nitroso and Oxime form

 

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

II > I (stability)

due to extended conjugation in (II)

Hydrazone and Azoform

NH2 NH2 (Hydrazine)

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

(extended conjugation)

Azo > Hydrazone (stability)

Ex.31 Compare enol percent.

(i) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(ii) Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

 

(iii) Structural Isomerism - Notes | Study 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 - Notes | Study Chemistry Class 11 - NEET →Structural Isomerism - Notes | Study Chemistry Class 11 - NEETStructural Isomerism - Notes | Study Chemistry Class 11 - NEET

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

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

 

Ring-chain Isomerism

Structural Isomerism - Notes | Study Chemistry Class 11 - NEET

If one isomer has 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 - Notes | Study Chemistry Class 11 - NEET

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

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

(iii) Alkenols and cyclic ethers, (CnH2nO)

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

Note : Ring-chain isomers are always functional isomers.

The document Structural Isomerism - Notes | Study Chemistry Class 11 - NEET is a part of the NEET Course Chemistry Class 11.
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