The standard 13C NMR spectrum of phenyl propanoate is shown here. Predict the appearance of the DEPT-90 and DEPT-135 spectra. <IMAGE>
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Step 1: Analyze the standard 13C NMR spectrum provided. Each peak corresponds to a unique carbon environment in phenyl propanoate. The labeled carbons (a, b, c, d, e, f, g, h) represent different chemical environments, including aromatic carbons, ester carbons, and alkyl carbons.
Step 2: Understand DEPT spectra. DEPT-90 shows only CH carbons, while DEPT-135 distinguishes CH and CH3 carbons (positive peaks) from CH2 carbons (negative peaks). Quaternary carbons (no hydrogens attached) do not appear in DEPT spectra.
Step 3: Identify the carbon types in phenyl propanoate. For example, carbon 'd' (carbonyl carbon) is quaternary and will not appear in DEPT spectra. Carbon 'a' (CH3) will appear as a positive peak in DEPT-135. Carbon 'b' (CH2) will appear as a negative peak in DEPT-135. Aromatic carbons (e, f, g, h) are CH carbons and will appear in both DEPT-90 and DEPT-135 as positive peaks.
Step 4: Predict the DEPT-90 spectrum. Only CH carbons will appear, so peaks corresponding to carbons e, f, g, and h will be visible. Other carbons (a, b, c, d) will not appear.
Step 5: Predict the DEPT-135 spectrum. Positive peaks will correspond to CH and CH3 carbons (a, e, f, g, h), while negative peaks will correspond to CH2 carbons (b). Quaternary carbons (d) will not appear.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
NMR Spectroscopy
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful analytical technique used to determine the structure of organic compounds. It exploits the magnetic properties of certain nuclei, such as carbon-13, to provide information about the number and environment of atoms in a molecule. The resulting spectra reveal details about the molecular framework, including the types of hydrogen and carbon present.
DEPT (Distortionless Enhancement by Polarization Transfer) is a specialized NMR technique that enhances the detection of specific types of carbon atoms in a molecule. DEPT-90 selectively shows only CH (methine) carbons, while DEPT-135 displays CH and CH3 (methyl) carbons as positive signals and CH2 (methylene) carbons as negative signals. These techniques help in distinguishing between different carbon environments and provide clarity in interpreting the carbon skeleton.
Phenyl propanoate is an ester formed from phenol and propanoic acid, characterized by a phenyl group attached to a propanoate moiety. Understanding its structure is crucial for predicting NMR spectra, as the arrangement of carbon atoms influences the chemical shifts observed in the DEPT spectra. The presence of aromatic and aliphatic carbons in phenyl propanoate will result in distinct patterns in the DEPT-90 and DEPT-135 spectra.