NEET · Chemistry —

Organic Chemistry - Some Basic Principles and Techniques appeared 3 times across 1 year — 6.7% of Chemistry. This question is from Qualitative Analysis of Organic Compounds.

Year 2024 Total
Questions 3 3
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During Lassaigne's test, the elements present in an organic compound are converted from :

Solution & Explanation

Core Logic

In an organic compound, elements like Nitrogen, Sulphur, and Halogens are bonded to Carbon via covalent bonds. During Lassaigne's test, the organic compound is fused with sodium metal. The high temperature and reactive sodium break the covalent bonds and convert these elements into water-soluble ionic sodium salts.

  • Carbon and Nitrogen form Sodium Cyanide (NaCN)
  • Sulphur forms Sodium Sulphide (Na₂S)
  • Halogens form Sodium Halides (NaX)
Step 1: Final Conclusion

The elements are converted from covalent form to ionic form to facilitate their detection using standard inorganic qualitative analysis.

Pattern Recognition

Sodium extract preparation (Lassaigne's fusion) always serves to ionize covalently bonded organic heteroatoms into inorganic sodium salts.

Chapter Mix

Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques

Reference Study Guides

Organic Chemistry Some Basic Principles And Techniques

More Organic Chemistry - Some Basic Principles and Techniques Previous-Year Questions

Q66 neet_2026_03_may_morning Isomerism
The pair of molecules that are metamers among the following is :
Isomerism diagram for Q66 - NEET 2026 Code 12
Displays structures in option 3 for identifying isomerism types among given pairs.
  • A. CH₃CH₂CH₂OH and CH₃-CH(OH)-CH₃
  • B. CH₃OCH₂CH₂CH₃ and CH₃CH₂OCH₂CH₃
  • C. Option featuring ketone pairs with differing chain branches
  • D. CH₃CH₂CH₂CH₂CH₃ & (CH₃)₂CHCH₂CH₃

Solution

Core Logic

Metamerism arises due to the presence of different alkyl chains on either side of the polyvalent functional group (such as -O-, -S-, -NH-, -CO-) in the molecule.

Evaluating the options: (1) CH₃CH₂CH₂OH (Propan-1-ol) and CH₃CH(OH)CH₃ (Propan-2-ol) are position isomers (OH group position changes). (2) CH₃-O-CH₂CH₂CH₃ (1-Methoxypropane) and CH₃CH₂-O-CH₂CH₃ (Ethoxyethane) have different alkyl groups attached to the central Oxygen atom. They are metamers. (3) The image structures represent chain isomers or position isomers depending on exact interpretation, but not metamers of a single unbroken functional bridge like ethers. (4) CH₃CH₂CH₂CH₂CH₃ (Pentane) and (CH₃)₂CHCH₂CH₃ (Isopentane) are chain isomers.

Step 1: Final Conclusion

The pair CH₃OCH₂CH₂CH₃ and CH₃CH₂OCH₂CH₃ are metamers.

Pattern Recognition

Metamerism requires a polyvalent bridging functional group like Ether (-O-), Thioether (-S-), Secondary Amine (-NH-), or Ketone (-CO-). Look for shifts in alkyl group boundaries across the bridge.

Chapter Mix

Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques

Q81 neet_2026_03_may_morning IUPAC Nomenclature
The correct IUPAC name of the following compound is : arrayc CH _ 3 - CH _ 2 - CH - CH _ 2 - CH - CH _ 2 - CH _ 3 | | CH _ 3 - CH _ 2 CH _ 3 array
  • A. 2,4-diethylhexane
  • B. 3,5-diethylhexane
  • C. 3-ethyl-5-methylheptane
  • D. 3-methyl-5-ethylheptane

Solution

Core Logic

Step 1: Identify the longest carbon chain. The longest continuous chain containing both substituents has 7 carbon atoms (heptane). Step 2: Number the chain to give the lowest possible locants to the substituents. Numbering from left to right gives substituents at positions 3 (ethyl) and 5 (methyl). Numbering right to left gives 3 (methyl) and 5 (ethyl). When locant sets are equivalent (3,5), alphabetical priority governs the numbering. 'Ethyl' comes before 'Methyl', so the ethyl group gets the lower number (3). Substituents: 3-ethyl and 5-methyl.

Solution for Q81 - IUPAC Numbering
Solution for Q81 - IUPAC Numbering

Step 1: Final Name

The correct IUPAC name is 3-ethyl-5-methylheptane.

Pattern Recognition

Always choose the longest chain first. If numbering from both ends yields the same locant set, default to alphabetical order for deciding which end starts at 1.

Chapter Mix

Class 11 Chemistry: Organic Chemistry - Some Basic Principles and Techniques

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