The third possible structure that is consistent with the IR spectrum in Figure 15-25 is to be drawn. Concept introduction: IR spectroscopy enables us to identify different functional groups in the molecule. One of the greatest advantages of IR spectroscopy is that the frequency of a particular type of vibration is typically found within a characteristic range of frequencies, regardless of the functional group with which the vibration is associated. The fact that absorptions by certain vibrations appear with characteristic frequency ranges enables us to use IR spectroscopy to obtain structural information about a molecule. For identifying correct structures from the given IR spectrum, the first step is to calculate the IHD from the given molecular formula of a compound. IHD accounts for the number of rings or multiple bonds the structure could possess. C=O absorption for a ketone is strong and relatively narrow that appears ~1710 − 1730 cm -1 . The conjugated C=C or C ≡ C bonds lowers the absorption frequency of C=O by 20 − 40 cm − 1 . The terminal alkene has strong two peaks around 910 and 990 cm − 1 . The absorption stretch for alkene C − H appears at 3050 cm − 1 .

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Chapter 15, Problem 15.27P

Interpretation Introduction

Interpretation:

The third possible structure that is consistent with the IR spectrum in Figure 15-25 is to be drawn.

Concept introduction:

IR spectroscopy enables us to identify different functional groups in the molecule.

One of the greatest advantages of IR spectroscopy is that the frequency of a particular type of vibration is typically found within a characteristic range of frequencies, regardless of the functional group with which the vibration is associated. The fact that absorptions by certain vibrations appear with characteristic frequency ranges enables us to use IR spectroscopy to obtain structural information about a molecule. For identifying correct structures from the given IR spectrum, the first step is to calculate the IHD from the given molecular formula of a compound. IHD accounts for the number of rings or multiple bonds the structure could possess. C=O absorption for a ketone is strong and relatively narrow that appears ~1710−1730 cm-1. The conjugated C=C or C≡C bonds lowers the absorption frequency of C=O by 20−40cm−1. The terminal alkene has strong two peaks around 910 and 990 cm−1. The absorption stretch for alkene C−H appears at 3050 cm−1.

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