Q13-21P - Organic Chemistry (Mcmurry)

Question

Estimate the chemical shift of each carbon in the following molecule. Predict which carbons will appear in the DEPT-90 spectrum, which will give positive peaks in the DEPT-135 spectrum, and which will give negative peaks in the DEPT-135 spectrum.

Step-by-Step Solution

Answer

$\mathrm{C}$ has subtracted DEPT-135 from a broadband-decoupled spectrum

$\text{CH}$DEPT-90

${\text{CH}}_{\text{2}}$ Negative DEPT-135

${\mathrm{CH}}_3$ Subtract DEPT-90 from positive DEPT-135

Step 1: DEPT- NMR technique

The DEPT–NMR, for distortionless enhancement by polarization transfer, which makes it possible to distinguish between signals due to ${\mathbf{CH}}_3\mathbf{,}{\mathbf{CH}}_2\mathbf{,}\mathbf{CH}$ , and quaternary carbons.

That is, the number of hydrogens attached to each carbon in a molecule can be determined.

Step 2: Peaks in DEPT-NMR

$\mathrm{C}$ has Subtract DEPT-135 from a broadband-decoupled spectrum

$\text{CH}$DEPT-90

${\text{CH}}_{\text{2}}$Negative DEPT-135

$C{H}_3$Subtract DEPT-90 from positive DEPT-135