Identify the most shielded and least shielded protons in(a) 2-Bromobutane(b) 1,1,2-Trichlo...

Identify the most shielded and least shielded protons in

(a) 2-Bromobutane

(b) 1,1,2-Trichloropropane

(c) Tetrahydrofuran:

Sample Solution (a) Bromine is electronegative and will have its greatest electron- withdrawing effect on protons that are separated from it by the fewest bonds. Therefore, the proton at C-2 will be the least shielded, and those at C-4 the most shielded.

The observed chemical shifts are δ 4.1 for the proton at C-2 and δ 1.1 for the protons at C-4. The protons at C-1 and C-3 appear in the range δ 1.7-2.0.