Q9P - Organic Chemistry (Mcmurry)

Question

The IR spectrum of phenylacetylene is shown in Figure 12-28. What absorptionbands can you identify?

Step-by-Step Solution

Answer

From the given absorption spectrum 4 peaks are seen: = C - H stretch in the alkyne group, aromatic ring = C - H stretch, - C =  C - stretch in the alkyne group,anaromatic ring - C =  C - motions.

Absorption spectrum

The absorption spectrum depicts the presence of dark lines in the spectrum when transmitted through a substance which indicates absorption at specific wavelengths of electromagnetic radiation.

Chart for absorption by specific functional group

The given chart tells the value of absorption of particular wavelength radiation by a specific functional group.

Peak is seen in the spectrum

From the given absorption spectrum 4 peaks can be seen:

• Absorption band at 3300 cm^-1  shows the absorption due to = C - H stretch in the alkyne group.
• Absorption bands at 3000-3100 cm^-1  are due to aromatic ring = C - H stretch.
• Absorption at 2100 cm^-1   is due to - C =  C - stretch in the alkyne group.
• Absorption at 1450-1600 is due to aromatic ring - C =  C - motions