Q13-15P - Organic Chemistry (Mcmurry)

Question

Question: 3-Bromo-1-phenyl-1-propene shows a complex NMR spectrum in which the vinylic proton at C2 is coupled with both the C1 vinylic proton (J = 16 Hz) and the C3 methylene protons (J = 8 Hz). Draw a tree diagram for the C2 proton signal, and account for the fact that a five-line multiplet is observed .

Step-by-Step Solution

Answer

                

Step 1: The splitting of signals in NMR

In NMR spectroscopy splitting is caused by the hydrogen atoms which lie on the same or on different carbon atoms.  

The signals are split by the non-equivalent protons only.

 

Step 2: The occurrence of splitting in 3-Bromo-1-phenyl-1-propene

When C2 is coupled with C1 then the signal is split into two lines having a J value of 16 Hz. When C2 couples with the C3 proton we get a triplet so we can say that the two lines are further split into three lines.

Hence, we get total of six lines

                            

                                         plitting of signals