Chapter 16, Problem 16.26P

Interpretation Introduction

Interpretation:

A splitting diagram similar to the one in Figure 16-25 for a quartet of triplets in which both the quartet and the triplet have the same coupling constant is to be constructed.

Concept introduction:

A complex splitting pattern is observed when a proton is coupled with two or more chemically disctinct protons. When a given proton is coupled with two types of chemically distinct protons, then two independent splitting patterns appear simultaneously. The size of the vicinal coupling constant between trans protons on a double bond is normally larger than that between cis protons. For the compounds in which vicinal protons are not equivalent, a proton ${\text{H}}_{\text{a}}$ is coupled with ${\text{H}}_{\text{b}}{\text{, H}}_{\text{c}}\text{, H}{\text{d}}_{}\text{, etc}\mathrm{..}$ with unequal coupling constants. The original signal for ${\text{H}}_{\text{a}}$ is split into $\text{(n+1)}$ peaks by ${\text{nH}}_{\text{b}}$ protons. Each of these lines is further split into $\text{(n+1)}$ peaks by ${\text{nH}}_{\text{c}}$ protons and each of these lines into $\text{(n+1)}$ peaks by ${\text{nH}}_{\text{d}}$ protons and so on.

To achieve quartet of triplets, the first coupling splits the signal into four peaks. The second coupling then splits each of those peaks into three peaks. Because the coupling constant is same for all those twelve lines, the pattern merges into six lines.