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पाईये Principles and Applications of Photochemical Reactions उत्तरे आणि तपशीलवार उपायांसह एकाधिक निवड प्रश्न (MCQ क्विझ). हे मोफत डाउनलोड करा Principles and Applications of Photochemical Reactions एमसीक्यू क्विझ पीडीएफ आणि बँकिंग, एसएससी, रेल्वे, यूपीएससी, स्टेट पीएससी यासारख्या तुमच्या आगामी परीक्षांची तयारी करा.

Latest Principles and Applications of Photochemical Reactions MCQ Objective Questions

Top Principles and Applications of Photochemical Reactions MCQ Objective Questions

Principles and Applications of Photochemical Reactions Question 1:

During photochemical reaction of alkenes having cis and trans isomer, photolysis causes generation of _________. 

  1. Mixture richer in trans isomer
  2. Mixture richer is cis isomer 
  3. Mixture containing only trans isomer
  4. Mixture containing only cis isomer

Answer (Detailed Solution Below)

Option 2 : Mixture richer is cis isomer 

Principles and Applications of Photochemical Reactions Question 1 Detailed Solution

The correct answer is Mixture richer is cis isomer 

Concept:-

  • Cis-Trans Isomerization: 
    Cis-trans isomerization involves the conversion of cis- and trans-isomers of alkenes into each other in the presence of UV light.
  • Energetics of Isomerization:
    The isomerization process is typically reversible. The relative stability of cis and trans isomers depends on the specific alkene.
  • Reaction Mechanism:
    During photolysis, the UV light provides energy to break the π bond in the alkene. The subsequent rearrangement can lead to the formation of both cis and trans isomers.

Explanation:-

Photochemical Reaction of Alkenes:

When alkenes undergo a photochemical reaction, such as photolysis in the presence of ultraviolet (UV) light, a process known as cis-trans isomerization can occur.

The answer "Mixture richer in cis isomer" suggests that, during the photochemical reaction, more cis isomers are generated compared to trans isomers.
The specific conditions and characteristics of the alkene determine the extent of isomerization and the relative stability of cis and trans isomers.

Cis-Trans isomerization of alkenes by direct irradiation
Because of the large energy absorptions, direct irradiation of the simplest alkenes (whose λmax is below 200 nm) is difficult to achieve.  the energy of a π → π* excited species is a function of the angle twist around the carbon-carbon (sigma) bond, and trans-to-cis-isomerization is thought to be affected by distortion of the trans-excited state initially produced, to an excited state common to both cis- and trans isomers.

A phantom state is the name given to this aroused state.In terms of the sample model, the cis-trans isomerization is triggered by the excitation of
an electron to a planar excited state, which then relaxes to the twisted state. The figure shows a simplified representation.

Twisting the planar trans singlet to the twisted singlet state requires a low activation energy of 2 kcal/mole. This twisted form can decompose into either cis or trans stilbene. However, as previously stated, the trans form absorbs more light at the exciting wavelength (εmax trans = 16300) than the cis form (max cis = 2880), and as a result, the trans isomer is almost fully transformed to the cis isomer.

F1 Savita Teaching 19-2-24 D19

Conclusion:-

The photolysis of alkenes leads to the generation of a mixture richer in the cis isomer.

Principles and Applications of Photochemical Reactions Question 2:

In the following sequence of pericyclic reactions X and Y are

qImage6613f151414af56a5f251101

  1. X = F1 Teaching Arbaz 11-10-23 D7, Y = hv/dis
  2. X = F1 Teaching Arbaz 11-10-23 D8, Y = hv/con
  3. X = F1 Teaching Arbaz 11-10-23 D7, Y = \(\Delta\)/dis
  4. X = F1 Teaching Arbaz 11-10-23 D8, Y = \(\Delta\)/con

Answer (Detailed Solution Below)

Option 3 : X = F1 Teaching Arbaz 11-10-23 D7, Y = \(\Delta\)/dis

Principles and Applications of Photochemical Reactions Question 2 Detailed Solution

The Chemical reaction involved in the above transformation can be illustrated as

F1 Teaching Arbaz 11-10-23 D9

Principles and Applications of Photochemical Reactions Question 3:

The major product formed in the following reaction sequence is

F1 Vinanti Teaching 28.09.23 D61

  1. F1 Vinanti Teaching 28.09.23 D62
  2. F1 Vinanti Teaching 28.09.23 D63
  3. F1 Vinanti Teaching 28.09.23 D64
  4. F1 Vinanti Teaching 28.09.23 D65

Answer (Detailed Solution Below)

Option 4 : F1 Vinanti Teaching 28.09.23 D65

Principles and Applications of Photochemical Reactions Question 3 Detailed Solution

Explanation:-

The reaction pathway is shown below:

F1 Vinanti Teaching 28.09.23 D66

Conclusion:-

  • Hence, the major product formed in the following reaction sequence is

F1 Vinanti Teaching 28.09.23 D65

Principles and Applications of Photochemical Reactions Question 4:

The major product formed in the sulfuric acid mediated rearrangement of the sesquiterpene saritonin A is

F1 Vinanti Teaching 28.09.23 D37

  1. F1 Vinanti Teaching 28.09.23 D38
  2. F1 Vinanti Teaching 28.09.23 D39
  3. F1 Vinanti Teaching 28.09.23 D40
  4. F1 Vinanti Teaching 28.09.23 D41

Answer (Detailed Solution Below)

Option 2 : F1 Vinanti Teaching 28.09.23 D39

Principles and Applications of Photochemical Reactions Question 4 Detailed Solution

The correct solution is option b

Concept:-

The dienone-phenol rearrangement is a type of organic reaction that involves the conversion of a dienone to a phenol or a phenolate by migration of a hydride ion (H⁻) or of an alkyl/aryl group.

This rearrangement reaction is usually facilitated under either basic or acidic conditions and can lead to the formation of sterically and electronically stabilized phenolic products from dienone precursors.

Here's a generalized sequence of steps for the dienone-phenol rearrangement:

  • Under basic conditions, deprotonation would happen at the α-carbon of the carbonyl group, which is actually the β-position of the dienone system. The deprotonated species then abstracts a proton from solvent, leading to a rearrangement with migration of a hydride from an α'-carbon (the carbon next to α-carbon).
  • If the reaction undergoes under acidic conditions, one of the carbonyl groups in dienone will be protonated first, followed by a rearrangement including a 1,2-alkyl or aryl shift.
  • In both cases, tautomers of phenol or phenolate will be generated.

The dienone-phenol rearrangement is synthetically very useful as it allows for the rearrangement of carbon skeletons and the formation of new carbon-oxygen bonds. This is particularly useful for synthesizing complex molecules and introduces a hydroxyl functional group that can undergo further reactions.

Explanation:- 

It is a type of dienone-phenol rearrangement.

step 1:Protonation of the carbonyl group 

step 2:The carbocation intermediate then undergoes a 1,2-alkyl

Step 3:Deprotonation of this intermediate

F1 Vinanti Teaching 28.09.23 D42

 

Conclusion:-

So, the  correct option is 2

Principles and Applications of Photochemical Reactions Question 5:

The mechanisms for the formation of molecules A and B involve, respectively.

F1 Savita Teaching 7-7-23 D20

  1. oxa-di-π-methane rearrangement and Norrish type II cleavage
  2. Norrish type I cleavage and oxa-di-t-methane rearrangement
  3. oxa-di-π-methane rearrangement and Norrish type I cleavage
  4. Norrish type I cleavage and Norrish type II cleavage

Answer (Detailed Solution Below)

Option 3 : oxa-di-π-methane rearrangement and Norrish type I cleavage

Principles and Applications of Photochemical Reactions Question 5 Detailed Solution

Concept: 

The mechanism of the reaction follows Norrish Type-I and Type-II reaction.

Norrish Type-I reaction involves photochemical cleavage of \(\alpha,\beta\)-unsaturated ketone/aldehyde group where as Norrish Type-II proceeds via photochemical abstraction of \(\gamma\)-hydrogen.

Example:

Norrish Type-I:
F3 Vinanti Teaching 29.05.23 D132

Norrish Type-II
F3 Vinanti Teaching 29.05.23 D133

Explanation:-

  • The reaction pathway for the formation of molecules A is as follows:

F1 Vinanti Teaching 10.07.23 D1

  • Thus, the mechanisms for the formation of molecules A involves oxa-di-π-methane rearrangement.
  • The reaction pathway for the formation of molecule B is as follows:

F1 Vinanti Teaching 10.07.23 D2

  • As, the \(\gamma\)-H present in the compound is far away from the carbonyl group, a Norrish type-II cleavge is not possible.
  • Thus, the mechanisms for the formation of molecule B involve Norrish type I cleavage.

Conclusion:-

Hence, the mechanisms for the formation of molecules A and B involve, respectively oxa-di-π-methane rearrangement and Norrish type I cleavage

Principles and Applications of Photochemical Reactions Question 6:

The diene that undergoes Diels - Alder reaction with maleic anhydride is:

  1. F1 Savita Teaching 22-5-23 D23
  2. F1 Savita Teaching 22-5-23 D24
  3. F1 Savita Teaching 22-5-23 D25
  4. F1 Savita Teaching 22-5-23 D26

Answer (Detailed Solution Below)

Option 2 : F1 Savita Teaching 22-5-23 D24

Principles and Applications of Photochemical Reactions Question 6 Detailed Solution

Concept:-

Diels–Alder reaction:

  • Diels–Alder reactions occur between a conjugated diene and an alkene, usually called the dienophile.
  • This reaction goes in a single step simply on heating.
  • Here are some examples: first an open-chain diene with a simple unsaturated aldehyde as the dienophile

F2 Savita Teaching 19-5-23 D41

Diene:

  • The diene component in the Diels–Alder reaction can be open-chain or cyclic and can have many different substituents.
  • There is only one limitation: The diene must have the s-cis conformation.
  • Butadiene typically prefers the s-trans conformation with the two double bonds as far away from each other as possible for steric reasons. The barrier to rotation about the central σ bond is small (about 30 kJ.mol−1 at room temperature) and rotation to the less favorable but reactive s-cis conformation is rapid.

F2 Savita Teaching 19-5-23 D42

  • Cyclic dienes that are permanently in the s-cis conformation are exceptionally good at Diels–Alder reactions—cyclopentadiene is a classic example—but cyclic dienes that are permanently in the s-trans conformation and cannot adopt the s-cis conformation will not do the
    Diels–Alder reaction at all.
  • Dienes permanently in the s-cis conformation are excellent for Diels–Alder reactions.

F2 Savita Teaching 19-5-23 D43

Explanation:-

  • The diene that undergoes Diels - Alder reaction with maleic anhydride must have an s-cis confirmation as follows:

F1 Savita Teaching 22-5-23 D27

  • Only the diene can undergo Diels - Alder reaction with maleic anhydride by attaining s-cis conformation

F1 Savita Teaching 22-5-23 D24

  • The reaction pathway is shown below:

F1 Savita Teaching 22-5-23 D28

  • The remaining dienes are locked in an s-trans conformation and hence do not react with maleic anhydride to give Diels - Alder reaction

Conclusion:-

  • Hence, he diene that undergoes Diels - Alder reaction with maleic anhydride is:

F1 Savita Teaching 22-5-23 D24

Principles and Applications of Photochemical Reactions Question 7:

In the given reaction, the major product is:

F2 Savita Teaching 19-5-23 D34

  1. F2 Savita Teaching 19-5-23 D35
  2. F2 Savita Teaching 19-5-23 D36
  3. F2 Savita Teaching 19-5-23 D37
  4. F2 Savita Teaching 19-5-23 D38

Answer (Detailed Solution Below)

Option 1 : F2 Savita Teaching 19-5-23 D35

Principles and Applications of Photochemical Reactions Question 7 Detailed Solution

Concept:-

​The Alder ‘ene’ reaction:

  • The Diels–Alder reaction was originally called the ‘diene reaction’ so when half of the famous team (Kurt Alder) discovered an analogous reaction that requires only one alkene, it was called the Alder ene reaction and the name has stuck. Compare here the Diels–Alder and the
    Alder ene reactions.
  • The below diagram explains the difference between a Diels–Alder reaction and an Alder ene reaction.

F2 Savita Teaching 19-5-23 D70

  • The simplest way to look at the ene reaction is to picture it as a Diels–Alder reaction in which one of the double bonds in the diene has been replaced by a C–H bond.
  • The reaction does not form a new ring, the product has only one new C–C bond, and a hydrogen atom is transferred across space. Otherwise, the two reactions are remarkably similar.

Explanation:

Mechanism:-

  • The reaction pathway is shown below:

F2 Savita Teaching 19-5-23 D39

  • Selective formation of the cis-disubstituted cyclopentane via intramolecular ene reaction is due to the fact that the transition state will be of lower energy if the hydrogen atoms are on the same side of the folded bicyclic structure. This constraint is similar in a way that a five-membered ring fused to a six-membered ring is lower in energy if it is cis-fused.

Conclusion:-

  • Hence, the given reaction, the major product is:

F2 Savita Teaching 19-5-23 D35

Principles and Applications of Photochemical Reactions Question 8:

The intermediate I and the major product II in the following conversion involves:

F2 Savita Teaching 19-5-23 D57

  1. Carbocation and F2 Savita Teaching 19-5-23 D58
  2. Carbanion and F2 Savita Teaching 19-5-23 D59
  3. Free radical and F2 Savita Teaching 19-5-23 D60
  4. Benzyne and F2 Savita Teaching 19-5-23 D61

Answer (Detailed Solution Below)

Option 4 : Benzyne and F2 Savita Teaching 19-5-23 D61

Principles and Applications of Photochemical Reactions Question 8 Detailed Solution

Concept:-

Diels-Alder reaction:

  • Diels-Alder reaction is a type of pericyclic reaction between an alkene (called dienophile) and a diene
  • The reaction proceeds through concerted mechanism.
  • It is a syn cycloaddition reaction and thus 'locked 'cis isomer favors the reactivity with dienophile.

Trapping reactive intermediates by cycloadditions:

  • The trapping of a reactive intermediates can be done in a Diels– Alder reaction. One way of generating benzyne for this purpose is the diazotization of anthranilic acid (2-aminobenzoic acid).

F2 Savita Teaching 19-5-23 D62

  • Benzyne may not look like a good dienophile but it is an unstable electrophilic molecule so it must have a low-energy LUMO (π* of the triple bond). If benzyne is generated in the presence of a diene, effi cient Diels–Alder reactions take place. Anthracene gives a specially interesting
    product with a symmetrical cage structure.

F2 Savita Teaching 19-5-23 D63

F2 Savita Teaching 19-5-23 D64

Explanation:-

Mechanism:

  • The reaction pathway is shown below:

F2 Savita Teaching 19-5-23 D65

  • Diazotization of anthranilic acid gives a diazonium salt, which on treatment with a mild base undergoes elimination of CO2 and N2 to give benzyne intermediate (I). It immediately undergoes Diels-Alder reaction to give II.

​Conclusion:-

  • Hence, the intermediate I and the major product II in the following conversion involves:

Benzyne and F2 Savita Teaching 19-5-23 D61

Principles and Applications of Photochemical Reactions Question 9:

The following reaction is an example of

F2 Savita Teaching 2-6-23 D1 V2

  1. [3 + 2] cycloaddition
  2. [4 + 2] cycloaddition
  3. [6 + 2] cycloaddition
  4. [8 + 2] cycloaddition 

Answer (Detailed Solution Below)

Option 4 : [8 + 2] cycloaddition 

Principles and Applications of Photochemical Reactions Question 9 Detailed Solution

Concept:-

Cycloaddition Reaction:

  • The cycloaddition reaction is a chemical reaction in which two or more unsaturated molecules combine with each other to form a cyclic compound, with a reduction of bond multiplicity.
  • In other words, cycloaddition reaction indicates the addition of two or more π-bonds to form a cyclic adduct with the formation of bonds at the end of the pi bonds.

Explanation:-

  • The given reaction is

F2 Savita Teaching 2-6-23 D1 V2

  • The reaction pathway is shown below:

F1 Savita Teaching 30-5-23 D32

  • The 8\(\pi\) electrons of the cyclic system react with the 2\(\pi\) electrons of ethene-1,1,2,2-tetracarbonitrile, 

Conclusion:-

  • Hence, the following reaction is an example of

[8 + 2] cycloaddition 

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