Q87E - Organic Chemistry (Mcmurry)

Question

The proton NMR spectrum for a compound with formula  is shown below. The infrared spectrum has a strong band at . The broadband-decoupled  NMR spectral results are tabulated along with the DEPT-135 and DEPT-90 information. Draw the structure of this compound.

Step-by-Step Solution

Answer

                                                 Assignment of ${}^{1}H$NMR spectrum

                                                    Assignment of ${}^{13}\mathrm{C}$ NMR spectrum

Step1: DEPT

By combining the DEPT-45, DEPT-90 and DEPT-135 spectra, it is possible to determine multiplicity of each carbon signal. The DEPT-135 gives signals of all protonated carbons but the signals of quaternary carbons are absent in all the DEPT spectra. The analysis of ${}^{13}C$DEPT is done on the basis of the following observations represented as:

                                                 Analysis of DEPT

Step 2: Structure of the compound

The assignment of the ${}^1\mathrm{H}$NMR spectrum of the molecule is as follows:

                                               Assignment of ${}^1\mathrm{H}$NMR spectrum

The IR peak at  $1711{\mathrm{cm}}^{-1}$ andNMR peak at 207 ppm confirms a carbonyl group of carbon. The assignment of the NMR spectrum of the ketone A is as follows: 

                                               Assignment of  ${}^{13}C$ NMR spectrum