which of the structures have a major peak between 1700 and 3000 cm⁻¹? (select all that apply).
which of the structures have a major peak between 1700 and 3000 cm⁻¹? (select all that apply).
Answer
Explanation:
Step1: Recall IR - absorption ranges
Infrared (IR) spectroscopy is used to identify functional groups in organic compounds. The $C - H$ stretching vibrations of aliphatic and aromatic $C - H$ bonds occur in the range of 2800 - 3000 $cm^{-1}$, and the $C=O$ stretching vibration of aldehydes occurs around 1700 - 1750 $cm^{-1}$.
Step2: Analyze the first structure
The first structure is a cyclohexyl - aldehyde. It has a $C=O$ group (aldehyde functional group) which has a strong absorption peak around 1700 - 1750 $cm^{-1}$ and $C - H$ stretching vibrations in the range of 2800 - 3000 $cm^{-1}$.
Step3: Analyze the second structure
The second structure is benzene. Benzene has $C - H$ stretching vibrations in the range of 3000 - 3100 $cm^{-1}$, but no strong absorption in the 1700 - 3000 $cm^{-1}$ range that would be considered a major peak in the context of the given range (the $C - H$ stretch is a relatively weak - medium intensity peak compared to $C=O$).
Step4: Analyze the third structure
The third structure is naphthalene. It also has $C - H$ stretching vibrations in the range of 3000 - 3100 $cm^{-1}$, but no strong absorption in the 1700 - 3000 $cm^{-1}$ range that would be considered a major peak in the context of the given range.
Answer:
The first structure (cyclohexyl - aldehyde) has a major peak between 1700 and 3000 $cm^{-1}$ due to the $C=O$ and $C - H$ stretching vibrations. So the answer is the first - structure option.