Aturan Woodward - Fieser | Dienon Terkonjugasi

Introduction

In this tutorial, we will explore the Woodward-Fieser rules, which are essential for calculating the maximum wavelength (lambda) of conjugated dienones. Understanding this concept is crucial for anyone studying organic chemistry, particularly in the context of UV-Vis spectroscopy. This guide will break down the steps necessary to apply these rules effectively.

Step 1: Understand the Structure of Dienones

• Definition: A dienone consists of two double bonds ("di" for two), a ketone group ("on"), and features conjugation.
• Structure: Familiarize yourself with the basic structure, which includes:
  • Two carbon-carbon double bonds (C=C)
  • A carbonyl group (C=O) attached to one of the carbons involved in a double bond.

Step 2: Gather Necessary Data

• Alkyl Substituents: Obtain a table of values for alkyl groups and their contributions to the maximum wavelength calculation. You can refer to the provided material from the second meeting.
• Identify Substituents: Note any substituents on the conjugated system, as these will influence the lambda value.

Step 3: Calculate the Base Value

• Base Value for Conjugation: Start with the base value for the conjugated system. For example, a simple dienone without substituents typically has a base wavelength (lambda) value assigned.
• Reference Chart: Use the Woodward-Fieser reference chart to find the initial lambda value based on the number of conjugated double bonds.

Step 4: Add Substituent Contributions

• Identify Contributions:
  • For each substituent, refer to the table you gathered in Step 2.
  • Add the corresponding values for alkyl groups or other substituents directly attached to the carbon skeleton.
• Example: If you have a methyl (–CH3) group, you will add its specific contribution to your base lambda value.

Step 5: Consider Additional Factors

• Electron-Withdrawing Groups: If your structure includes groups that withdraw electrons (e.g., –NO2, –CN), adjust your calculation accordingly, as these will lower the lambda value.
• Electron-Donating Groups: Conversely, groups that donate electrons (e.g., –OCH3, –NH2) will increase the lambda value.

Step 6: Final Calculation

• Total Lambda Value: Combine the base value with all the contributions from substituents and any adjustments made for electron-withdrawing or donating groups.
• Result Verification: Check your calculations against known values or examples to ensure accuracy.

Conclusion

By following these steps, you can effectively use the Woodward-Fieser rules to calculate the maximum wavelength of conjugated dienones. Remember to pay close attention to the structure and substituents, as they significantly impact your results. For further practice, consider applying these steps to various examples to reinforce your understanding. Happy studying!