Question

Each of these four structures has molecular formula . Match the structure with its characteristic proton NMR signals. (Not all of the signals are listed in each case.)

(a) Sharpsinglet atδ8.0 andtriplet atδ4.0

(b) Sharpsinglet atδ2.0 andquartet atδ4.1

(c) Sharpsinglet atδ3.7 andquartet atδ2.3

(d) Broadsinglet atδ11.5 andtriplet atδ2.3

Short answer

The given structures are matched with their characteristic proton NMR signals in each case.

Protons are shown in bold which gives NMR signals

Step-by-step solution

Step-1. Explanation of part (a):

The description of chemical shift and signals of part (a) matches with structure 4. In structure 4, there exists a sharp singlet of 1 hydrogen atom which is attached to the carbonyl carbon and its chemical shift value is 8.0. The two hydrogen atoms exhibit triplet pattern due to adjacent methylene hydrogen atoms and their chemical shift value is 4.0 due to attachment with oxygen which is electronegative.

Structure matched with given description

Step-2. Explanation of part (b):

The description of chemical shift and signals of part (b) matches with structure 3. In structure 3, there exists a sharp three hydrogen singlet of methyl group at chemical shift 2.0 and quartet for two hydrogens at chemical shift 4.1 due to presence of adjacent three hydrogens of methyl which splits the signal for these two hydrogen atoms into quartet.

Structure matched with given description

Step-3. Explanation of part (c):

The description of chemical shift and signals of part (c) matches with structure 2. In structure 2, there exists a sharp three hydrogen singlet at chemical shift 3.7 of methoxy group hydrogens. Hydrogen atoms of methylene group which are adjacent to carbonyl group shows quartet splitting pattern due to presence of three hydrogens of methyl group adjacent to it and have chemical shift value 2.3.

Structure matched with given description

Step-4. Explanation of part (d):

The description of chemical shift and signals of part (d) matches with structure 1. In structure 1, there exists a broad singlet of hydrogen of a hydroxyl group. The signal is broad due to acidic hydrogen of hydroxyl group which is exchangeable. The chemical shift value of this hydrogen is high due to direct attachment with electronegative atom like oxygen. The hydrogens of methylene group which are adjacent to carboxylic group shows a triplet pattern due to two hydrogens adjacent to it and shows chemical shift 2.3.

Structure matched with given description