Match List-I with List-II.
| List-I (Scientist) | List-II (Contribution) |
|---|---|
| (A) Louis Pasteur | (I) Rule for the preferred alkene in dehydrohalogenation reactions |
| (B) J. Van’t Hoff and C. Le Bel | (II) Discovery of the effectiveness of DDT as an insecticide |
| (C) Alexander Zaitsev | (III) Observation that crystals of certain compounds exist as mirror images |
| (D) Paul Muller | (IV) Tetrahedral arrangement of four groups around a central carbon atom |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A-III, B-IV, C-I, D-II
(A) Louis Pasteur — This matches (III) Observation that crystals of certain compounds exist as mirror images. This observation laid the foundation of modern stereochemistry.
(B) J. Van’t Hoff and C. Le Bel — This matches (IV) Tetrahedral arrangement of four groups around a central carbon atom. They argued that when all four groups on such a carbon are different, the molecule and its mirror image do not overlap; that carbon is an asymmetric carbon (stereocentre).
(C) Alexander Zaitsev — This matches (I) Rule for the preferred alkene in dehydrohalogenation reactions. By his rule, the major alkene is the one with more alkyl groups on the doubly bonded carbons.
(D) Paul Muller — This matches (II) Discovery of the effectiveness of DDT as an insecticide. DDT had been made long before, but he found its use as an insecticide.
NCERT (2026-27 edition):
6.7.1 Reactions of Haloalkanes – “(ii) Molecular asymmetry, chirality and enantiomers: The observation of Louis Pasteur (1848) that crystals of certain compounds exist in the form of mirror images laid the foundation of modern stereochemistry.”
“Dutch scientist, J. Van’t Hoff and French scientist, C. Le Bel in the same year (1874), independently argued that the spatial arrangement of four groups (valencies) around a central carbon is tetrahedral and if all the substituents attached to that carbon are different, the mirror image of the molecule is not superimposed (overlapped) on the molecule; such a carbon is called asymmetric carbon or stereocentre.”
“…These form part of a pattern first observed by Russian chemist, Alexander Zaitsev (also pronounced as Saytzeff) who in 1875 formulated a rule which can be summarised as ‘in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms.’”
6.8.6 p,p’-Dichlorodiphenyltrichloroethane (DDT) – “DDT, the first chlorinated organic insecticides, was originally prepared in 1873, but it was not until 1939 that Paul Muller … discovered the effectiveness of DDT as an insecticide.”