Chapter 16.13, Problem 29PTS

Interpretation Introduction

Interpretation: The structure of an alcohol of given molecular formula ${\text{C}}_5{\text{H}}_{\text{12}}\text{O}$ to be predicted using ${}^{\text{13}}\text{C}\text{NMR}$ spectra.

Concept Introduction:

The ${}^{\text{13}}\text{C}\text{NMR}$ spectrum gives information on the different electronic environments of carbon. As like ${}^{\text{1}}\text{H}\text{NMR}$, the number of signals generated in ${}^{\text{13}}\text{C}\text{NMR}$ are predicted by performing symmetry operations (rotation or reflection symmetry). Only chemical shift values are reported in the spectrum but not the multiplicity and integration values because the coupling between two neighboring ${}^{\text{13}}\text{C}{-}^{\text{13}}\text{C}$ nuclei are weakly involved due to the low abundance of ${}^{\text{13}}\text{C}$ isotopes of carbon atom.

Broadband-decoupled ${}^{\text{13}}\text{C}\text{NMR}$spectrum: The spectra provide information regarding the total number of carbon environments.

DEPT (Distortionless enhancement by polarization transfer):

DEPT $\text{-90}$: The spectrum exhibits signal only from $\text{CH}$ group and no signals from ${\text{CH}}_{\text{3}}$, ${\text{CH}}_{\text{2}}$, $\text{CH}$ and quaternary carbon (carbon with no protons).

DEPT $\text{-135}$: The spectrum exhibits ${\text{CH}}_3$ groups and $\text{CH}$ groups as positive signals (pointing up); ${\text{CH}}_2$ groups appear as negative signals (pointing down) and quaternary carbon does not appear.

The signals appear in each type of spectrum:

	${\text{CH}}_3$	${\text{CH}}_2$	$\text{CH}$	(Quaternary carbon)
BROADBAND DECOUPLED
DEPT $\text{-90}$	$\text{-}$	$\text{-}$		$\text{-}$
DEPT $\text{-135}$				$\text{-}$