DEPT-135

Definition

DEPT-135 is a type of 13C NMR spectroscopy technique that allows for the differentiation of carbon atoms based on their degree of protonation. It provides valuable information about the structure and connectivity of organic compounds by selectively enhancing the signals of methine (CH), methylene (CH2), and quaternary (C) carbons.

5 Must Know Facts For Your Next Test

1. DEPT-135 is a variation of the DEPT pulse sequence that provides information about the protonation state of carbon atoms in organic compounds.
2. The DEPT-135 experiment selectively enhances the signals of methine (CH) and quaternary (C) carbons, while suppressing the signals of methylene (CH2) carbons.
3. The 135-degree pulse angle in the DEPT-135 sequence is responsible for the selective enhancement of CH and C signals, while inverting the CH2 signals.
4. DEPT-135 is particularly useful for distinguishing between primary (CH3), secondary (CH2), tertiary (CH), and quaternary (C) carbon environments in organic molecules.
5. The DEPT-135 technique is often used in combination with other 13C NMR experiments, such as DEPT-90 and DEPT-45, to provide a comprehensive understanding of the carbon skeleton of organic compounds.

Review Questions

• Explain the principle behind the DEPT-135 technique and how it differs from standard 13C NMR spectroscopy.
  • The DEPT-135 technique is a variation of the Distortionless Enhancement by Polarization Transfer (DEPT) pulse sequence used in 13C NMR spectroscopy. Unlike standard 13C NMR, which provides information about all carbon environments in a molecule, DEPT-135 selectively enhances the signals of methine (CH) and quaternary (C) carbons, while suppressing the signals of methylene (CH2) carbons. This is achieved through the use of a 135-degree pulse angle, which inverts the CH2 signals while preserving the CH and C signals. This selective enhancement allows for easier identification of the different carbon environments within the organic compound.
• Describe how the DEPT-135 technique can be used to differentiate between primary, secondary, tertiary, and quaternary carbon environments in organic molecules.
  • The DEPT-135 experiment is particularly useful for distinguishing between different carbon environments in organic compounds. Primary (CH3) carbons will show positive signals, tertiary (CH) carbons will show positive signals, and quaternary (C) carbons will show positive signals. Methylene (CH2) carbons, on the other hand, will show negative signals due to the inversion caused by the 135-degree pulse angle. By analyzing the patterns and intensities of the signals in a DEPT-135 spectrum, you can readily identify the protonation state of the carbon atoms and infer the overall structure of the organic molecule.
• Discuss the advantages of using the DEPT-135 technique in combination with other 13C NMR experiments, such as DEPT-90 and DEPT-45, to obtain a comprehensive understanding of the carbon skeleton of organic compounds.
  • The DEPT-135 technique is often used in conjunction with other DEPT experiments, such as DEPT-90 and DEPT-45, to provide a more complete picture of the carbon skeleton in organic molecules. DEPT-90 selectively enhances the signals of tertiary (CH) carbons, while DEPT-45 enhances the signals of both primary (CH3) and tertiary (CH) carbons. By combining the information from these different DEPT experiments, you can unambiguously assign the protonation state of each carbon atom and gain a deeper understanding of the overall structure and connectivity of the organic compound. This comprehensive approach, using multiple DEPT techniques, is particularly valuable when analyzing complex organic molecules with various carbon environments.

Related terms

13C NMR Spectroscopy: A powerful analytical technique that utilizes the magnetic properties of carbon-13 nuclei to determine the structure and connectivity of organic molecules.

Proton Decoupling: A method in NMR spectroscopy that removes the coupling between carbon and hydrogen nuclei, simplifying the 13C NMR spectrum.

Distortionless Enhancement by Polarization Transfer (DEPT): A pulse sequence in 13C NMR spectroscopy that selectively enhances the signals of different carbon environments based on their degree of protonation.