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Lab Report: Predicting and Interpreting IR Spectra

Use this template to document all steps, observations, and analyses from your virtual lab. Provide detailed information at each stage. Where relevant, you may include screenshots, tables, and figures to support your findings.

1. Have Your Molecule Name Here

  • Your Ethanol Name:
    (e.g., “FirstnameLastname Ethanol (C₂H₅OH)”)
  • Your Acetone Name:
    (e.g., “FirstnameLastname Acetone (C₃H₆O)”)
  • Your Styrene Name:
    (e.g., “FirstnameLastname Styrene (C₈H₈)”)

Tip

Remember to incorporate your name and the molecule formula to personalize each molecule’s name.

2. Building the Molecule in QOOL

  1. Construction Steps
    Provide a concise, step-by-step description (2–3 sentences per molecule) of how you built each structure in QOOL.
  2. Ethanol: How you connected the carbons, added hydrogens, and placed the hydroxyl group.
  3. Acetone: How you formed the carbonyl (C=O) group and attached methyl groups.

  4. Styrene: How you created the benzene ring, attached the vinyl group, etc.

  5. Optimize the Geometry

  6. Before running any calculations, optimize the molecular geometry to minimize energy and achieve a realistic conformation.
  7. Briefly note any key observations during optimization (e.g., changes in bond angles, reorganization of substituents).
Screenshot: Molecule Model in QOOL
**Screenshot:** Example of Methanol Geometry in QOOL (Replace with your own.)

Submit Your Molecule Model Screenshot Here
- Ethanol:
(Insert screenshot showing your final Ethanol geometry.) - Acetone:
(Insert screenshot showing your final Acetone geometry.) - Styrene:
(Insert screenshot showing your final Styrene geometry.)

3. Setting Up the IR Spectrum Calculation

  1. Calculation Setup
  2. Describe the calculation type chosen (e.g., “Vibrational Frequencies” or “Optimize + Vib Freq”).
  3. Specify the method (e.g., B3LYP, ωB97X-D, PBE0) and basis set (e.g., 6-31G(d), 6-311+G(d,p)) you selected.

  4. Include any charge or multiplicity settings (usually 0 charge, singlet multiplicity for neutral organic molecules).

  5. Screenshot of Your Settings

  6. Provide a screenshot of the QOOL input parameters showing method, basis set, and any other options.
Screenshot: IR Calculation Setup
**Screenshot:** Example IR Spectrum Calculation Setup (Replace with your own.)

Upload Your Setup Screenshot Here
- Ethanol:
(Insert your screenshot for Ethanol’s IR calculation.) - Acetone:
(Insert your screenshot for Acetone’s IR calculation.) - Styrene:
(Insert your screenshot for Styrene’s IR calculation.)

4. Running the Calculation

  1. Submission
  2. Describe how you reviewed all settings for accuracy before submitting.

  3. Note any specific details about computational time or resources.

  4. Job Numbers (Optional)

  5. Your Job # for Ethanol: ___________
  6. Your Job # for Acetone: ___________
  7. Your Job # for Styrene: ___________

Note

Depending on the QOOL interface, job IDs or submission references may help you track calculations.

5. Analyzing the IR Spectrum

Once the calculations are complete:

  1. Access the Results

  2. Download or view the IR spectrum from QOOL for each molecule.

  3. Identify Absorption Peaks

  4. Note significant peaks (in cm⁻¹) that appear in the IR spectrum.

  5. Pay special attention to peaks that indicate O–H, C=O, aromatic C–H, etc.

  6. Assign Peaks to Functional Groups

  7. Consult IR reference charts (or textbook tables) to assign vibrations to specific peaks.

  8. Discuss how you confirmed each assignment.

  9. Interpret the Spectrum

  10. Summarize how each functional group is represented in the IR data (e.g., broad O–H band, sharp C=O stretch).
  11. Consider any effects (e.g., hydrogen bonding, conjugation, ring systems, etc.) that might shift or broaden the peaks.

Upload Your IR Spectrum Table Here
- Ethanol:
(Insert IR spectrum table or screenshot with labeled peaks.) - Acetone:
(Insert IR spectrum table or screenshot with labeled peaks.) - Styrene:
(Insert IR spectrum table or screenshot with labeled peaks.)

6. Data Recording

Provide tables documenting the observed peaks and their corresponding functional groups for each molecule. Add or remove rows as needed.

Ethanol IR Spectrum Key Peaks

Observed Wavenumber (cm⁻¹) Assigned Vibration Functional Group

Acetone IR Spectrum Key Peaks

Observed Wavenumber (cm⁻¹) Assigned Vibration Functional Group

Styrene IR Spectrum Key Peaks

Observed Wavenumber (cm⁻¹) Assigned Vibration Functional Group

Tip

  • Fingerprint Region (1500–500 cm⁻¹) can be complex but may still offer diagnostic peaks for aromatic ring substituents or subtle structural features.

Post-Lab Questions

Address each question thoroughly using full sentences and evidence from your spectra:

  1. Why is the O–H stretch in ethanol broad compared to other absorption peaks?
    (Answer here.)

  2. How does hydrogen bonding influence the IR spectrum of ethanol?
    (Answer here.)

  3. Explain why the C=O stretch in acetone appears as a strong, sharp peak.
    (Answer here.)

  4. What factors affect the exact position of the carbonyl stretch in the IR spectrum?
    (Answer here.)

  5. Identify the peaks associated with the aromatic C–H stretches in styrene.
    (Answer here.)

  6. Discuss how conjugation in the aromatic ring affects the absorption frequencies.
    (Answer here.)

  7. Compare the IR spectra of ethanol and acetone. How do the spectra reflect differences in their functional groups?
    (Answer here.)

  8. What challenges might you face when interpreting the IR spectrum of a molecule with multiple functional groups?
    (Answer here.)

  9. How can IR spectroscopy be used in conjunction with other analytical techniques for structural determination?
    (Answer here.)

  10. Discuss the importance of the fingerprint region (1500–500 cm⁻¹) in IR spectroscopy.
    (Answer here.)

Conclusion

Provide a concise summary of your findings:

  • Key learnings from the IR spectra of ethanol, acetone, and styrene.
  • Effectiveness of computational IR spectroscopy in identifying functional groups.
  • How this lab enhanced your understanding of molecular structure and IR theory.

References

  • Textbook: McMurry, J. Organic Chemistry, 10th Edition (Chapters on Spectroscopy).
  • QOOL User Guides: (Include any tutorials or guides you used.)
  • IR Spectroscopy Reference Charts: (List charts or online resources for peak assignments.)

Appendix

(Include any additional data, screenshots, or calculations here.)

Additional Screenshot
**Figure:** Example of Additional Data

End of Lab Report Template
When complete, submit your lab report per the course’s instructions. Make sure to include all requested materials (screenshots, spectra, tables) to earn full credit.