Discussion
The correct match of compounds given in Column I with spectral data given in column II is :
| Column I | Column II |
|---|---|
| (a) 1, 2-Dichloroethane | (i) λmax 220 nm |
| (b) 1, 4-Dibromobenzene | (ii) Only one singlet at 3.7 δ in 1H - NMR spectrum |
| (c) 2-Methyl-1,3-butadiene | (iii) Peaks at 234, 236, 238 m/e with intensity (1 : 2 : 1) in MS-spectrum |
| (d) Cyclopropane | (iv) Absorption at 1815 cm−1 in IR spectrum |
Answer: B
The correct match is (a-ii), (b-iii), (c-i), (d-iv).
- (a) 1,2-Dichloroethane, ClCH2CH2Cl: all four protons are equivalent, so the 1H NMR spectrum is a single singlet, near 3.7 δ.
- (b) 1,4-Dibromobenzene, C6H4Br2 (M = 234 with two 79Br): bromine has two isotopes, 79Br and 81Br, in nearly equal amounts, so a dibromide shows M, M+2 and M+4 peaks at 234, 236 and 238 in the ratio 1 : 2 : 1.
- (c) 2-Methyl-1,3-butadiene (isoprene) is a conjugated diene, with λmax near 220 nm.
Those three pairings are found only in option (B), which leaves (d) cyclopropane with (iv). Every other option mismatches at least one of (a) to (c), for example by giving the dibromide the single NMR singlet.
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