Organic Chemistry

21. In which of the following, functional group isomerism is not possible?

In which of the following, functional group isomerism is not possible?

[amp_mcq option1=”Alcohols” option2=”Aldehydes” option3=”Alkyl halides” option4=”Cyanides” correct=”option3″]

This question was previously asked in
UPSC CDS-1 – 2019
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The correct option is C.
Functional group isomerism involves compounds with the same molecular formula but different functional groups. Alcohols and ethers are functional group isomers (e.g., ethanol and dimethyl ether). Aldehydes and ketones are functional group isomers (e.g., propanal and propanone). Cyanides and isocyanides are functional group isomers (e.g., methyl cyanide and methyl isocyanide). Simple alkyl halides (R-X) generally do not have common functional group isomers with the same molecular formula; positional isomerism (different position of X on the carbon chain) is possible, but not a different functional group itself that is isomeric to an alkyl halide.
Isomers share the same molecular formula but differ in the arrangement of atoms. Different types of isomerism include structural isomerism (chain, positional, functional group, metamerism, tautomerism) and stereoisomerism (geometric and optical). Functional group isomerism is a type of structural isomerism.

22. Which one of the following elements cannot be detected by “Lassaigne’s

Which one of the following elements cannot be detected by “Lassaigne’s test”?

[amp_mcq option1=”I” option2=”Cl” option3=”S” option4=”F” correct=”option4″]

This question was previously asked in
UPSC CDS-1 – 2019
Download PDFAttempt Online
Lassaigne’s test (Sodium Fusion Test) is used to detect the presence of elements like nitrogen, sulfur, and halogens (chlorine, bromine, iodine) in an organic compound. The organic substance is fused with metallic sodium, converting these elements into ionic compounds (e.g., NaCN, Na2S, NaCl, NaBr, NaI) which are then extracted with water and tested for using specific reagents. Fluorine (F) is a halogen, but Lassaigne’s test is generally not used or is unreliable for its detection because sodium fluoride (NaF) is less soluble than other sodium halides, and organic fluoro compounds may not completely decompose to ionic fluoride upon fusion. Therefore, fluorine cannot be reliably detected by Lassaigne’s test.
– Lassaigne’s test detects N, S, Cl, Br, and I in organic compounds.
– Fluorine (F) is typically not detectable by Lassaigne’s test due to difficulties in forming and dissolving ionic fluoride.
For detecting fluorine in organic compounds, alternative methods like combustion followed by fluoride ion-selective electrode measurement or gravimetric analysis as calcium fluoride are used.
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