Ans.B Explanation: For this we must know the basic principles of nmr. Electrons

Question

Ans.B

Explanation:

For this we must know the basic principles of nmr.

Electrons orbiting around the nucleus generate a small magnetic field that opposes external magnetic field B0. In this case we say that electrons are shielding the nucleus from B0.

Up field or Shielding:
The higher the electron density around the nucleus, the higher the opposing magnetic field to B0 from the electrons, the greater the shielding. Because the proton experiences lower external magnetic field, it needs a lower frequency to achieve resonance, and therefore, the chemical shift shifts upfield (lower ppms) .

Down field or Deshielding:
If the electron density around a nucleus decreases, the opposing magnetic field becomes small and therefore, the nucleus feels more the external magnetic field B0, and therefore it is said to be deshielded. Because the proton experiences higher external magnetic field, it needs a higher frequency to achieve resonance, and therefore, the chemical shift shifts downfield (higher ppms) .

In case of 1,1-bromoethane

H3C2 - C1H (Br)2

Here the single proton on C-1 is splitted to quartet according to (n+1) rule, where n is the no.of neighbouring protons (here n=3) ,so a quartet. Also Bromine atoms are electronegative atom that will pull the electron density toward it , resulting in a deshielding or down field. Thus we get down field quartet.

Similarly Hydrogen nucleus is shielded in the case of protons on C-2, therefore the peak appears on the up field. And accordingto (n+1) rule, n=1 ,so splitting is doublet. Thus we get up field doublet.

Explanation / Answer

why

104 splitting in their IIu. (CHs)2CH-O-CHs IV Br-CHCHBr Which of the following compounds would be expected to show spin-spin H NMR spectra? L. (CHs)sC-O-CHs I. Br-CH CH CH2-Br V. CI Cl Qu D W,II.IV (E) ,IV,V (C) hy 104 Question 29 The proton NMR of 1,1-dibromoethane would appears a: C) downfield doublet and upfield triplet ld quartet Bdownfield quartet and upfield doublet D) downfield triplet and upfield doublet. [104.102 Question 30 The compounds shown below can be distinguished by which 'H-NMR characteris tics?

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