(a) (c) 100 % Transmittance % Transmittance 80 60- 40 20 0. 4000 100- 80 60- 40 20. 0 4000 12.4 Which IR spectrum is consistent with an alkene? 3500 3000 2500 2000 1500 1000 Wavenumber (cm^¹) 3500 3000 n 2500 2000 Wavenumber (cm¹) 1500 1000 (b) (d) 100- % Transmittance 80 % Transmittance 60 40 20- 0. 4000 100- 80 60- 40 20 0 4000 3500 3500 3000 3000 2500 2000 Wavenumber (cm¹) 2500 2000 Wavenumber (cm-¹) 1500 1000 1500 1000

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Which IR spectrum is consistent with an alkene?

**12.4 Which IR spectrum is consistent with an alkene?**

The image displays four infrared (IR) spectra labeled (a), (b), (c), and (d). Each spectrum charts the percentage of transmittance against the wavenumber in cm⁻¹. 

**Spectrum (a):** 
- Major absorptions around 3300 cm⁻¹ and 1650 cm⁻¹, indicating the presence of a possible NH or OH bond.
- The region between 1000-1500 cm⁻¹ shows multiple peaks, typical of complex molecular vibrations.

**Spectrum (b):**
- A broad absorption near 3400 cm⁻¹, suggestive of an OH group.
- A strong peak around 1700 cm⁻¹, characteristic of a C=O bond, likely not consistent with an alkene.

**Spectrum (c):**
- Exhibits a sharp peak around 1600 cm⁻¹, indicative of a C=C bond, which is characteristic of alkenes.
- No broad peaks near 3300 cm⁻¹, ruling out OH or NH groups.

**Spectrum (d):**
- Displays a single sharp peak near 1700 cm⁻¹, suggesting the presence of a C=O bond.
- Lacks significant features indicative of an alkene, such as a C=C stretch.

**Conclusion:**
Spectrum (c) is consistent with an alkene due to the presence of a peak around 1600 cm⁻¹, aligning with the C=C stretching frequency characteristic of alkenes.
Transcribed Image Text:**12.4 Which IR spectrum is consistent with an alkene?** The image displays four infrared (IR) spectra labeled (a), (b), (c), and (d). Each spectrum charts the percentage of transmittance against the wavenumber in cm⁻¹. **Spectrum (a):** - Major absorptions around 3300 cm⁻¹ and 1650 cm⁻¹, indicating the presence of a possible NH or OH bond. - The region between 1000-1500 cm⁻¹ shows multiple peaks, typical of complex molecular vibrations. **Spectrum (b):** - A broad absorption near 3400 cm⁻¹, suggestive of an OH group. - A strong peak around 1700 cm⁻¹, characteristic of a C=O bond, likely not consistent with an alkene. **Spectrum (c):** - Exhibits a sharp peak around 1600 cm⁻¹, indicative of a C=C bond, which is characteristic of alkenes. - No broad peaks near 3300 cm⁻¹, ruling out OH or NH groups. **Spectrum (d):** - Displays a single sharp peak near 1700 cm⁻¹, suggesting the presence of a C=O bond. - Lacks significant features indicative of an alkene, such as a C=C stretch. **Conclusion:** Spectrum (c) is consistent with an alkene due to the presence of a peak around 1600 cm⁻¹, aligning with the C=C stretching frequency characteristic of alkenes.
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Ir spectroscopy helps in identification of the different functional group environment present in the molecule by measuring their stretching/bending frequencies etc.

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