Organic Chemistry – Some Basic Principles & Techniques NEET PYQs
Practice NEET previous year questions from Organic Chemistry – Some Basic Principles & Techniques. These MCQs cover inductive effect, hyperconjugation, carbocation stability, nucleophile–electrophile concept, tautomerism, purification techniques and quantitative analysis with answers and explanations.
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Organic Chemistry – Some Basic Principles & Techniques Notes
Q1. Which of the following carbocations is expected to be the most stable?
(NEET 2018)
- (A) Primary carbocation
- (B) Secondary carbocation
- (C) Tertiary carbocation
- (D) Methyl carbocation
Show Answer
(C)
Show Explanation
Tertiary carbocation is most stable due to maximum hyperconjugation and +I effect of alkyl groups.
Q2. Which order of −I effect of substituents is correct?
(NEET 2018)
- (A) −NH2 < −OR < −F
- (B) −F < −OR < −NH2
- (C) −OR < −NH2 < −F
- (D) −NH2 < −F < −OR
Show Answer
(A)
Show Explanation
−I effect increases with electronegativity: F > OR > NH2.
Q3. The most suitable method for separation of a 1:1 mixture of ortho- and para-nitrophenol is:
(NEET 2017)
- (A) Chromatography
- (B) Crystallisation
- (C) Steam distillation
- (D) Sublimation
Show Answer
(C)
Show Explanation
o-Nitrophenol is steam volatile due to intramolecular hydrogen bonding.
Q4. The correct statement regarding electrophile is:
(NEET 2017)
- (A) Negatively charged species
- (B) Neutral species donating electrons
- (C) Neutral or positively charged species accepting electrons
- (D) Negatively charged electron acceptor
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(C)
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Electrophiles are electron-deficient species that accept electron pairs.
Q5. Which of the following compounds can exhibit tautomerism?
(NEET 2016)
- (A) Only I
- (B) Only II
- (C) I and III
- (D) All of these
Show Answer
(D)
Show Explanation
Keto-enol tautomerism occurs in compounds having α-hydrogen atoms.
Q6. Which statement is not correct for a nucleophile?
(NEET 2015)
- (A) Ammonia is a nucleophile
- (B) Nucleophiles attack low electron density sites
- (C) Nucleophiles are not electron seeking
- (D) Nucleophile is a Lewis acid
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(D)
Show Explanation
Nucleophiles are Lewis bases, not Lewis acids.
Q7. Hyperconjugation occurs in:
(NEET 2015)
- (A) I only
- (B) II only
- (C) III only
- (D) I and III
Show Answer
(C)
Show Explanation
Hyperconjugation requires α-hydrogen atoms attached to sp2/sp carbon.
Q8. In Kjeldahl’s method, nitrogen present in compound is converted into:
(NEET 2014)
- (A) N2
- (B) NH3
- (C) NO2
- (D) NaCN
Show Answer
(B)
Show Explanation
Nitrogen is converted into ammonia during digestion.
Q9. The radical is aromatic because it has:
(NEET 2013)
- (A) 7 π-electrons
- (B) 6 π-electrons
- (C) 8 π-electrons
- (D) 4 π-electrons
Show Answer
(B)
Show Explanation
Aromaticity follows Huckel’s rule: 4n+2 π electrons.
Q10. The most reactive compound towards electrophilic nitration is:
(NEET 2013)
- (A) Nitrobenzene
- (B) Benzoic acid
- (C) Benzene
- (D) Toluene
Show Answer
(D)
Show Explanation
Methyl group activates the benzene ring by +I effect.
Q11. Which one shows geometrical isomerism?
(NEET 2002)
- (A) Ethane
- (B) Propene
- (C) 1,2-Dichloroethene
- (D) Methane
Show Answer
(C)
Show Explanation
Restricted rotation around C=C bond causes cis-trans isomerism.
Q12. The shortest C–C bond length is found in:
(NEET 1991)
- (A) Ethane
- (B) Ethene
- (C) Benzene
- (D) Ethyne
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(D)
Show Explanation
Triple bond has highest bond order and shortest bond length.
Q13. Which is the best antiknocking agent?
(NEET 1996)
- (A) Ethanol
- (B) Glyoxal
- (C) Freon
- (D) Tetraethyl lead
Show Answer
(D)
Show Explanation
Tetraethyl lead reduces knocking in petrol engines.
Q14. The molecular formula of diphenylmethane is:
(NEET 2004)
- (A) C13H12
- (B) C12H10
- (C) C13H10
- (D) C14H12
Show Answer
(A)
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Diphenylmethane = (C6H5)2CH2.
Q15. Which fertilizer has the highest nitrogen percentage?
(NEET 1993)
- (A) Ammonium sulphate
- (B) Calcium cyanamide
- (C) Urea
- (D) Ammonium nitrate
Show Answer
(C)
Show Explanation
Urea contains about 46.6% nitrogen.
Q16. Which method is best for purification of cyclohexanone?
(NEET 1997)
- (A) Sublimation
- (B) Evaporation
- (C) Crystallisation
- (D) IR spectroscopy
Show Answer
(D)
Show Explanation
IR spectroscopy identifies carbonyl group specifically.
Q17. Which one is a nucleophilic substitution reaction?
(NEET 2011)
- (A) Elimination
- (B) Addition
- (C) Substitution
- (D) Rearrangement
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(C)
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Nucleophile replaces leaving group in substitution reactions.
Q18. The number of structural isomers of C5H12 is:
(NEET 1996)
- (A) 2
- (B) 3
- (C) 4
- (D) 5
Show Answer
(B)
Show Explanation
n-Pentane, isopentane and neopentane.
Q19. The hybridisation of carbon in benzene is:
(NEET 1991)
- (A) sp
- (B) sp2
- (C) sp3
- (D) dsp2
Show Answer
(B)
Show Explanation
Each carbon in benzene is sp2 hybridised.
Q20. Isomers must have the same:
(NEET 1991)
- (A) Structural formula
- (B) Physical properties
- (C) Chemical properties
- (D) Molecular formula
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(D)
Show Explanation
Isomers differ in structure but have same molecular formula.
👉 More Organic Chemistry NEET PYQs will be added gradually.