1H NMR spectrum of [18]-annulene at low temperature shows:

(c) दो शिखर δ 9.0 (12H) तथा δ −3.0 (6H) परtwo peaks at δ 9.0 (12H) and δ −3.0 (6H)

(a) केवल एक शिखर δ 7.2 (18H) परonly one peak at δ 7.2 (18H)

(b) केवल एक शिखर δ 5.0 (18H) परonly one peak at δ 5.0 (18H)

(c) दो शिखर δ 9.0 (12H) तथा δ −3.0 (6H) परtwo peaks at δ 9.0 (12H) and δ −3.0 (6H)

(d) दो शिखर δ 9.0 (6H) तथा δ −3.0 (12H) परtwo peaks at δ 9.0 (6H) and δ −3.0 (12H)

The correct statement about C60 is:

(a) C60 बेंजीन में घुलनशील हैC60 is soluble in benzene

(b) C60 तृतीयक-ब्यूटिललीथियम के साथ अभिक्रिया नहीं करता हैC60 does not react with tert-butyllithium

(c) C60 10 पांच-सदस्यीय तथा 15 छह-सदस्यीय वलयों से बना हैC60 is made up of 10 five-membered and 15 six-membered rings

(d) दो आसन्न पांच-सदस्यीय वलय एक उभयनिष्ठ भुजा साझा करते हैंTwo adjacent five-membered rings share a common edge

The compound that is NOT aromatic is:(a)+(b)−(c)−(d)−−

(b) संरचना (b)Structure (b)

(a) संरचना (a)Structure (a)

(b) संरचना (b)Structure (b)

(c) संरचना (c)Structure (c)

(d) संरचना (d)Structure (d)

The most acidic species is:(a)NHH+(b)NHH+(c)NH+(d)NH+NMe2

(b) स्पीशीज (b)Species (b)

(a) स्पीशीज (a)Species (a)

(b) स्पीशीज (b)Species (b)

(c) स्पीशीज (c)Species (c)

(d) स्पीशीज (d)Species (d)

The compound A (Azulene) shown below is:A

(a) एरोमैटिक है तथा इसका द्विध्रुव आघूर्ण उच्च हैaromatic and has high dipole moment

(b) एरोमैटिक है तथा इसका कोई द्विध्रुव आघूर्ण नहीं हैaromatic and has no dipole moment

(c) अन-एरोमैटिक है तथा इसका द्विध्रुव आघूर्ण उच्च हैnon-aromatic and has high dipole moment

(d) प्रति-एरोमैटिक है तथा इसका कोई द्विध्रुव आघूर्ण नहीं हैanti-aromatic and has no dipole moment

Among the following compounds, the one that is non-aromatic, is:(a)(b)(c)(d)

(a) यौगिक (a)Compound (a)

(b) यौगिक (b)Compound (b)

(c) यौगिक (c)Compound (c)

(d) यौगिक (d)Compound (d)

Among the carbocations given below:HH+A+B+C

(a) A सम-एरोमैटिक (homoaromatic), B प्रति-एरोमैटिक (antiaromatic) तथा C एरोमैटिक है।A is homoaromatic, B is antiaromatic and C is aromatic.

(b) A एरोमैटिक, B प्रति-एरोमैटिक तथा C सम-एरोमैटिक है।A is aromatic, B is antiaromatic and C is homoaromatic.

(c) A प्रति-एरोमैटिक, B एरोमैटिक तथा C सम-एरोमैटिक है।A is antiaromatic, B is aromatic and C is homoaromatic.

(d) A सम-एरोमैटिक, B एरोमैटिक तथा C प्रति-एरोमैटिक है।A is homoaromatic, B is aromatic and C is antiaromatic.

Among A–C, the aromatic compounds are:HHABCH2C

(c) केवल B तथा CB and C only

(b) केवल A तथा BA and B only

(c) केवल B तथा CB and C only

(d) केवल A तथा CA and C only

With respect to electrophilic aromatic substitution, reactivity order of pyrrole, pyridine and indole is:

(c) pyrrole > indole > pyridine

(a) indole > pyrrole > pyridine

(b) pyrrole > pyridine > indole

(c) pyrrole > indole > pyridine

(d) indole > pyridine > pyrrole

Consider the following statements for [18]-annulene:(A) It is aromatic.(B) The inner protons resonate at δ 9.28 in its 1H NMR spectrum.(C) There are six protons in the shielded zone.The correct statements are:HHHHHHHHHHHHHHHHHH

(d) केवल A तथा CA and C only

(b) केवल A तथा BA and B only

(c) केवल B तथा CB and C only

(d) केवल A तथा CA and C only

Among the following, the compound which has the lowest energy barrier for the cis-trans isomerisation is:(a)(b)(c)(d)

(c) यौगिक (c)Compound (c)

(a) यौगिक (a)Compound (a)

(b) यौगिक (b)Compound (b)

(c) यौगिक (c)Compound (c)

(d) यौगिक (d)Compound (d)

The compound that gives precipitate on warming with aqueous AgNO3 is:(a)Br(b)Br(c)Br(d)BrN

(c) यौगिक (c)Compound (c)

(a) यौगिक (a)Compound (a)

(b) यौगिक (b)Compound (b)

(c) यौगिक (c)Compound (c)

(d) यौगिक (d)Compound (d)

The correct statement about the following species A and B is:++AOB

(b) A एरोमैटिक है तथा B प्रति-एरोमैटिक हैA is aromatic and B is antiaromatic

(a) A तथा B दोनों एरोमैटिक हैंBoth A and B are aromatic

(b) A एरोमैटिक है तथा B प्रति-एरोमैटिक हैA is aromatic and B is antiaromatic

(c) A अन-एरोमैटिक है तथा B प्रति-एरोमैटic हैA is nonaromatic and B is antiaromatic

(d) A एरोमैटिक है तथा B सम-एरोमैटिक हैA is aromatic and B is homoaromatic

Among the following compounds, the one which has highest dipole moment is:(a)(b)(c)(d)

(b) संरचना (b)Structure (b)

(a) संरचना (a)Structure (a)

(b) संरचना (b)Structure (b)

(c) संरचना (c)Structure (c)

(d) संरचना (d)Structure (d)

The correct match of the 1H NMR chemical shifts δ of the following species/compound is:−III+III

(a) I : 5.4; II : 7.2; III : 9.2

(b) I : 9.2; II : 7.2; III : 5.4

(c) I : 9.2; II : 5.4; III : 7.2

(d) I : 7.2; II : 9.2; III : 5.4

Correct match for the products of the reactions in Column A with the properties in Column B is:i.+ 2Kii.+ H2SO4iii.HHheativ.+ 2KColumn A (Reaction)Column B (Property of Product)(i) Cyclooctatetraene + 2 KP. Aromatic(ii) Cyclooctatetraene + H2SO4Q. Antiaromatic(iii) Bicyclo[4.2.0]octa-2,4,7-triene + heatR. Non-aromatic(iv) trans-10b,10c-Dimethyldihydropyrene + 2 KS. Homoaromatic

(a) i – P, ii – S, iii – R, iv – Q

(b) i – P, ii – R, iii – Q, iv – S

(c) i – Q, ii – R, iii – S, iv – P

(d) i – S, ii – Q, iii – R, iv – P

The correct match of the circled protons in Column P with the 1H NMR chemical shift (δ ppm) in Column Q is:HIOHIIHIIIColumn P (Circled Proton)Column Q (Chemical Shift, δ ppm)I. Inner proton of [12]annuleneA. 6.72II. Proton of troponeB. 16.4III. Inner proton of [14]annuleneC. −0.61

(b) I – B; II – A; III – C

(a) I – A; II – B; III – C

(b) I – B; II – A; III – C

(c) I – B; II – C; III – A

(d) I – C; II – B; III – A

SOLVED PYQ GUIDE CSIR-UGC NET Part B & C GATE Chemistry Non-Benzenoid Systems

CSIR NET Chemical Science: Aromaticity PYQs with Detailed Solutions

Master Hückel’s rule, diatropic/paratropic ¹H-NMR shifts, annulene planarity, Craig’s rule, and Baird’s excited-state aromaticity with categorized previous year questions and step-by-step solutions.

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6–12 Marks Exam Weightage

Part B & C 2 & 4 Mark Questions

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📋 Table of Contents

CSIR NET Aromaticity: Topic Weightage & Trend Analysis
Essential Diagnostic Rules for Solving PYQs
अभ्यास मोड (Practice Mode)
Detailed Solution & Exam Trick (विस्तृत हल व परीक्षा ट्रिक)
Categorized PYQs with Step-by-Step Solutions
Quick-Reference Identification Matrix
Frequently Asked Questions (FAQs)

CSIR NET Aromaticity: Topic Weightage & Trend Analysis

Aromaticity and non-benzenoid conjugated systems are among the most dependable scoring topics in Organic Chemistry. Review the distribution pattern below:

Exam Component	Typical Question Count	Marks Weightage	Common Question Formats
Part B	1 to 2 Questions	2 to 4 Marks	Direct classification (Aromatic vs Antiaromatic vs Non-aromatic), simple heterocycles, charged ions.
Part C	1 to 2 Questions	4 to 8 Marks	Annulene conformations, ¹H-NMR diatropic/paratropic shifts, Craig’s rule, Baird aromaticity, quasi-aromatic dipoles.
Total Impact	2 to 3 Questions	6 to 12 Marks	Consistently tested in June and December cycles.

Essential Diagnostic Rules for Solving PYQs

Before attempting the previous year problems, revise these core theoretical criteria:

1. Hückel’s Rule (4n + 2 π-Electrons)

Applies strictly to planar, monocyclic, fully conjugated systems.
Aromatic: (4n + 2) π-electrons (where n = 0, 1, 2, 3, …).
Antiaromatic: 4n π-electrons (where n = 1, 2, 3, …) in a planar ring.
Non-Aromatic: Any system lacking planarity, having broken conjugation (sp³ carbons), or open-chain polyenes.

2. Annulene Planarity & NMR Criteria

[8]-Annulene (Cyclooctatetraene): Adopts a non-planar tub conformation to relieve angle strain; non-aromatic.
[10]-Annulene: Non-planar due to steric clash between internal 1,6-hydrogens; non-aromatic unless bridged (e.g., 1,6-methano[10]annulene is planar and aromatic).
[14] and [18]-Annulenes: [14] is weakly aromatic due to residual steric crowding, whereas [18]-annulene is planar and strongly aromatic with outer protons at δ ≈ +9.28 ppm and inner protons at δ ≈ −2.99 ppm.

3. Specialized Systems (Craig’s, Baird’s & Quasi-Aromatic)

Homoaromaticity: Conjugation bypassed through space across one or more sp³ carbons (e.g., homotropylium cation).
Quasi-Aromatic: Systems with a predominant dipolar resonance contributor satisfying (4n + 2) π-electrons (e.g., Tropone, Azulene).
Craig’s Rule (Polycyclics): For non-benzenoid systems with a C_2v symmetry plane: if (N − f) is a multiple of 2, the molecule is non-aromatic/antiaromatic; if odd, it is aromatic.
Baird’s Rule (Excited Triplet State T₁): Rule inverts in the lowest triplet excited state—4n π-systems become aromatic and stabilized, while (4n + 2) π-systems become antiaromatic.

CSIR NET JRF Aromaticity PYQs

🎯 General Examination — Negative Marking Applicable

Question No. 01 | Section A

MCQ | Correct: +2.0 | Incorrect: -0.50

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📖 Test Questions & Syllabus Outline (Google Search Index & Study Reference) Total: 24 Questions

This online mock test covers the following chemistry practice questions with bilingual explanations, negative marking schemes, and interactive CBT interface. Students searching for these topics can practice the complete test online with real-time timers:

1H NMR spectrum of [18]-annulene at low temperature shows: GATE — Aromaticity
कम तापमान पर [18]-ऐनुलीन का 1H NMR स्पेक्ट्रम दर्शाता है:
The correct order of the basicity of the following compounds is:NHINHIINIIINHIV GATE — Aromaticity
निम्नलिखित नाइट्रोजन-युक्त यौगिकों की क्षारकता (basicity) का सही क्रम है:NHINHIINIIINHIV
The correct statement about C60 is: GATE — Aromaticity
बकमिंस्टरफुलेरीन (C60) के संबंध में सही कथन है:
The compound that is NOT aromatic is:(a)+(b)−(c)−(d)−− GATE — Aromaticity
निम्नलिखित में से कौन-सा यौगिक एरोमैटिक (aromatic) नहीं है?(a)+(b)−(c)−(d)−−
The most acidic species is:(a)NHH+(b)NHH+(c)NH+(d)NH+NMe2 GATE — Aromaticity
निम्नलिखित में से सर्वाधिक अम्लीय (most acidic) स्पीशीज है:(a)NHH+(b)NHH+(c)NH+(d)NH+NMe2
The compound A (Azulene) shown below is:A GATE — Aromaticity
नीचे दर्शाया गया यौगिक A (एज़ूलीन) है:A
The decreasing order of the reactivity of the following compounds towards electrophiles is:NHISIINIII GATE — Aromaticity
इलेक्ट्रॉनस्नेही (electrophiles) के प्रति निम्नलिखित यौगिकों की क्रियाशीलता का घटता हुआ क्रम है:NHISIINIII
The decreasing order of the acidity of the marked H of the following molecules is:HHIHHIIHIII GATE — Aromaticity
निम्नलिखित अणुओं के चिह्नित H की अम्लीयता (acidity) का घटता क्रम है:HHIHHIIHIII
Among the following compounds, the one that is non-aromatic, is:(a)(b)(c)(d) GATE — Aromaticity
निम्नलिखित यौगिकों में से कौन-सा यौगिक अन-एरोमैटिक (non-aromatic) है?(a)(b)(c)(d)
Among the following, the total number of aromatic species is ________.O1O+2+34+5−6NH7−8 GATE — Aromaticity
निम्नलिखित आठ स्पीशीज में से, एरोमैटिक स्पीशीज की कुल संख्या ________ है।O1O+2+34+5−6NH7−8
Among the carbocations given below:HH+A+B+C CSIR NET Part B — Aromaticity
नीचे दिए गए कार्बधनायनों (carbocations) के संबंध में सही कथन है:HH+A+B+C
Among A–C, the aromatic compounds are:HHABCH2C CSIR NET Part B — Aromaticity
A–C में से, एरोमैटिक यौगिक हैं:HHABCH2C
With respect to electrophilic aromatic substitution, reactivity order of pyrrole, pyridine and indole is: CSIR NET Part B — Aromaticity
इलेक्ट्रॉनस्नेही एरोमैटिक प्रतिस्थापन (electrophilic aromatic substitution) के प्रति पाइरोल, पिरिडीन तथा इन्डोल की क्रियाशीलता का क्रम है:
Consider the following statements for [18]-annulene:(A) It is aromatic.(B) The inner protons resonate at δ 9.28 in its 1H NMR spectrum.(C) There are six protons in the shielded zone.The correct statements are:HHHHHHHHHHHHHHHHHH CSIR NET Part B — Aromaticity
[18]-ऐनुलीन के लिए निम्नलिखित कथनों पर विचार कीजिए:(A) यह एरोमैटिक है।(B) इसके 1H NMR स्पेक्ट्रम में आंतरिक प्रोटॉन δ 9.28 पर अनुनाद करते हैं।(C) परिरक्षित क्षेत्र (shielded zone) में छह प्रोटॉन उपस्थित हैं।सही कथन हैं:HHHHHHHHHHHHHHHHHH
Among the following, the compound which has the lowest energy barrier for the cis-trans isomerisation is:(a)(b)(c)(d) CSIR NET Part B — Aromaticity
निम्नलिखित में से किस यौगिक में सिस-ट्रांस समावयवीकरण (cis-trans isomerisation) के लिए ऊर्जा अवरोध (energy barrier) न्यूनतम है?(a)(b)(c)(d)
The compound that gives precipitate on warming with aqueous AgNO3 is:(a)Br(b)Br(c)Br(d)BrN CSIR NET Part B — Aromaticity
वह यौगिक जो जलीय AgNO3 के साथ गर्म करने पर अवक्षेप (precipitate) देता है, वह है:(a)Br(b)Br(c)Br(d)BrN
The correct statement about the following species A and B is:++AOB CSIR NET Part B — Aromaticity
निम्नलिखित स्पीशीज A तथा B के संबंध में सही कथन है:++AOB
The correct order of acidity of the following compounds A–C is:CF3CF3F3CCF3F3CAHBC CSIR NET Part C — Aromaticity
निम्नलिखित यौगिकों A–C की अम्लीयता (acidity) का सही क्रम है:CF3CF3F3CCF3F3CAHBC
Among the following compounds, the one which has highest dipole moment is:(a)(b)(c)(d) CSIR NET Part C — Aromaticity
निम्नलिखित यौगिकों में से किसका द्विध्रुव आघूर्ण (dipole moment) उच्चतम है?(a)(b)(c)(d)
The correct match of the 1H NMR chemical shifts δ of the following species/compound is:−III+III CSIR NET Part C — Aromaticity
निम्नलिखित स्पीशीज/यौगिकों के 1H NMR रासायनिक विस्थापन (chemical shifts, δ ppm) का सही सुमेल है:−III+III
The compound that is antiaromatic is:BHI+IIIIIOIV CSIR NET Part C — Aromaticity
निम्नलिखित में से कौन-सा यौगिक प्रति-एरोमैटिक (antiaromatic) है?BHI+IIIIIOIV
Correct match for the products of the reactions in Column A with the properties in Column B is:i.+ 2Kii.+ H2SO4iii.HHheativ.+ 2KColumn A (Reaction)Column B (Property of Product)(i) Cyclooctatetraene + 2 KP. Aromatic(ii) Cyclooctatetraene + H2SO4Q. Antiaromatic(iii) Bicyclo[4.2.0]octa-2,4,7-triene + heatR. Non-aromatic(iv) trans-10b,10c-Dimethyldihydropyrene + 2 KS. Homoaromatic CSIR NET Part C — Aromaticity
कॉलम A में दी गई अभिक्रियाओं के उत्पादों का कॉलम B में दिए गए गुणों से सही सुमेलन है:i.+ 2Kii.+ H2SO4iii.HHheativ.+ 2Kकॉलम A (अभिक्रिया)कॉलम B (उत्पाद का गुण)(i) साइक्लोऑक्टाटेट्राईन + 2 KP. एरोमैटिक (Aromatic)(ii) साइक्लोऑक्टाटेट्राईन + H2SO4Q. प्रति-एरोमैटिक (Antiaromatic)(iii) बाइसाइक्लो[4.2.0]ऑक्टा-2,4,7-ट्राईन + ऊष्माR. अन-एरोमैटिक (Non-aromatic)(iv) ट्रांस-10b,10c-डाइमेथिलडाइहाइड्रोपाइरीन + 2 KS. सम-एरोमैटिक (Homoaromatic)
The correct match of the circled protons in Column P with the 1H NMR chemical shift (δ ppm) in Column Q is:HIOHIIHIIIColumn P (Circled Proton)Column Q (Chemical Shift, δ ppm)I. Inner proton of [12]annuleneA. 6.72II. Proton of troponeB. 16.4III. Inner proton of [14]annuleneC. −0.61 CSIR NET Part C — Aromaticity
कॉलम P में चिह्नित (घेरे गए) प्रोटॉनों का कॉलम Q में 1H NMR रासायनिक विस्थापन (δ ppm) के साथ सही सुमेलन है:HIOHIIHIIIकॉलम P (घेरे गए प्रोटॉन)कॉलम Q (रासायनिक विस्थापन, δ ppm)I. [12]ऐनुलीन का आंतरिक प्रोटॉनA. 6.72II. ट्रोपोन का प्रोटॉनB. 16.4III. [14]ऐनुलीन का आंतरिक प्रोटॉनC. −0.61
The correct match of protons in Column A with the 1H NMR chemical shift (δ ppm) in Column B for the homotropylium cation is:H1H7H2H3H4H5H6HAHB+Column A (Proton)Column B (Chemical Shift, δ ppm)P. HA (exo proton)i. −0.3Q. HB (endo proton)ii. 5.1R. H1 & H7iii. 6.4S. H2 – H6iv. 8.5 CSIR NET Part C — Aromaticity
होमोट्रोपिलियम धनायन (homotropylium cation) के लिए कॉलम A के प्रोटॉनों का कॉलम B के 1H NMR रासायनिक विस्थापन (δ ppm) के साथ सही सुमेलन है:H1H7H2H3H4H5H6HAHB+कॉलम A (प्रोटॉन)कॉलम B (रासायनिक विस्थापन, δ ppm)P. HA (बाहरी / exo प्रोटॉन)i. −0.3Q. HB (आंतरिक / endo प्रोटॉन)ii. 5.1R. H1 तथा H7iii. 6.4S. H2 – H6iv. 8.5

Categorized PYQs with Step-by-Step Solutions

Type 1: Annulenes & ¹H-NMR Spectroscopy (Part C)

Question 1: In the ¹H-NMR spectrum of [18]-annulene recorded at −60°C, the ratio of peak areas and their respective chemical shift values are:

(A) 12H at δ 9.28 ppm (outer) and 6H at δ −2.99 ppm (inner)
(B) 6H at δ 9.28 ppm (outer) and 12H at δ −2.99 ppm (inner)
(C) 18H single peak at δ 5.40 ppm
(D) 12H at δ −2.99 ppm (outer) and 6H at δ 9.28 ppm (inner)

Correct Answer: (A)
Detailed Explanation:
1. [18]-Annulene contains 18 π-electrons (4n + 2, n = 4), forming an aromatic diatropic system.
2. The diamagnetic ring current reinforces the applied external magnetic field outside the ring (deshielding 12 outer protons to δ ≈ 9.28 ppm) and opposes the field inside the perimeter (shielding 6 inner protons to δ ≈ −2.99 ppm).
3. The intensity ratio is 12H : 6H (2:1).

Type 2: Charged Species & Quasi-Aromatic Systems (Part B)

Question 2: Among the following compounds, the one that displays a high dipole moment and behaves as an aromatic salt is:

(A) Cyclopentadiene
(B) Cycloheptatrienone (Tropone)
(C) Cyclooctatetraene
(D) 1,3-Cyclohexadiene

Correct Answer: (B)
Detailed Explanation:
1. Tropone (cycloheptatrienone) possesses a highly polar carbonyl group: C=O ↔ C⁺−O⁻.
2. Polarization places a positive charge onto the seven-membered ring, generating an aromatic 6 π-electron tropylium cation core.
3. This quasi-aromatic resonance contributor endows tropone with high thermodynamic stability and an unusually large dipole moment (≈ 4.3 D).

Type 3: Antiaromatic vs Non-Aromatic Classification (Part B/C)

Question 3: Consider the following species: (1) Pentalene, (2) Cyclopropenyl cation, (3) Cyclopentadienyl cation, (4) Azulene. The pair of antiaromatic species among them is:

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

Correct Answer: (B)
Detailed Explanation:
• Pentalene (1): Planar, bicyclic 8 π-electron system (4n, n = 2); antiaromatic.
• Cyclopropenyl cation (2): 2 π-electrons (4n + 2, n = 0); stable aromatic.
• Cyclopentadienyl cation (3): 4 π-electrons (4n, n = 1); planar antiaromatic.
• Azulene (4): 10 π-electrons (4n + 2, n = 2); non-benzenoid aromatic.
Therefore, species 1 and 3 are antiaromatic.

Quick-Reference Identification Matrix

Species / Ring System	π-Electrons	Geometry / Conformation	Classification	Characteristic Diagnostic Feature
Cyclopropenyl Cation	2	Planar	Aromatic	High pK_R⁺ stability
Cyclobutadiene	4	Rectangular distortion	Antiaromatic	Jahn-Teller distortion, dimerizes rapidly
Cyclopentadienyl Anion	6	Planar regular pentagon	Aromatic	Common η⁵ ligand in ferrocene
Tropylium Ion	6	Planar regular heptagon	Aromatic	Forms stable bromide and fluoroborate salts
Cyclooctatetraene (COT)	8	Tub-shaped (D_2d)	Non-Aromatic	Conjugated polyene behavior, addition reactions
COT Dianion (C₈H₈²⁻)	10	Planar regular octagon	Aromatic	Formed by 2e reduction with Potassium metal
Homotropylium Cation	6	Non-planar (sp³ bridge)	Homoaromatic	CH₂ bridge excluded from π-overlap
1,6-Methano[10]annulene	10	Bridged perimeter	Aromatic	Peripheral delocalization, diatropic NMR

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Frequently Asked Questions (FAQs)

What is the primary difference between antiaromatic and non-aromatic compounds?

Antiaromatic compounds are planar, cyclic, and fully conjugated with 4n π-electrons, resulting in substantial electronic destabilization compared to acyclic polyenes. Non-aromatic compounds fail one or more essential criteria (such as planarity or continuous conjugation), exhibiting stability similar to typical open-chain alkenes.

Why is [10]-annulene non-aromatic despite having 10 pi electrons?

Although it satisfies the (4n + 2) count (n = 2), steric crowding between internal hydrogens at C-1 and C-6 prevents the carbon ring from achieving planarity. Without planar p-orbital overlap, it behaves as a non-aromatic conjugated polyene.

How does Baird’s rule apply to photochemical reactions in CSIR NET?

Baird’s rule states that in the lowest triplet excited state (T₁), 4n π-systems become aromatic and stabilized, while (4n + 2) π-systems become antiaromatic and destabilized. This principle explains photochemical ring-opening and pericyclic reaction pathways.

CSIR NET Chemical Science: Aromaticity PYQs with Detailed Solutions (PDF Download)

CSIR NET Chemical Science: Aromaticity PYQs with Detailed Solutions

CSIR NET Aromaticity: Topic Weightage & Trend Analysis

Essential Diagnostic Rules for Solving PYQs

1. Hückel’s Rule (4n + 2 π-Electrons)

2. Annulene Planarity & NMR Criteria

3. Specialized Systems (Craig’s, Baird’s & Quasi-Aromatic)

Categorized PYQs with Step-by-Step Solutions

Quick-Reference Identification Matrix

Frequently Asked Questions (FAQs)

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CSIR NET Chemical Science: Aromaticity PYQs with Detailed Solutions

CSIR NET Aromaticity: Topic Weightage & Trend Analysis

Essential Diagnostic Rules for Solving PYQs

1. Hückel’s Rule (4n + 2 π-Electrons)

2. Annulene Planarity & NMR Criteria

3. Specialized Systems (Craig’s, Baird’s & Quasi-Aromatic)

अभ्यास मोड (Practice Mode)

Categorized PYQs with Step-by-Step Solutions

Quick-Reference Identification Matrix

Frequently Asked Questions (FAQs)

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