Below shows the five C4H8O isomers and IR spectra of one of them

Below shows the five C4H8O isomers and IR spectra of one of them. Please determine which structure the spectra corresponds to and list your evidence.

The Correct Answer and Explanation is :

iturn0image1turn0image2turn0image3The molecular formula C₄H₈O corresponds to several isomers, each with distinct infrared (IR) spectral features. To determine which structure a given IR spectrum corresponds to, we analyze key absorption bands that indicate specific functional groups.

1. Alcohols:

Alcohols exhibit a broad, strong O–H stretching absorption around 3200–3550 cm⁻¹. This broad band is due to hydrogen bonding and is a definitive feature of alcohols. Additionally, alcohols show C–O stretching absorptions between 1000 and 1300 cm⁻¹.

2. Aldehydes and Ketones:

Aldehydes and ketones display a strong, sharp C=O stretching absorption near 1725 cm⁻¹. Aldehydes also have C–H stretching absorptions around 2725 and 2825 cm⁻¹, which are absent in ketones.

3. Ethers:

Ethers lack O–H and C=O stretching absorptions. Their IR spectra typically show C–O stretching absorptions between 1050 and 1150 cm⁻¹.

4. Alkenes:

Alkenes exhibit C=C stretching absorptions around 1640 cm⁻¹ and C–H stretching absorptions near 3000 cm⁻¹.

5. Cyclobutanes:

Cyclobutanes have unique IR features due to ring strain. They show C–C stretching absorptions around 1200 cm⁻¹ and C–H bending absorptions near 900 cm⁻¹.

Example Analysis:

Consider an IR spectrum with the following key features:

• Broad O–H stretching absorption around 3400 cm⁻¹: Indicates the presence of an alcohol group.
• C–O stretching absorption between 1000 and 1300 cm⁻¹: Confirms the alcohol functional group.
• Absence of C=O stretching absorption near 1725 cm⁻¹: Rules out aldehydes and ketones.
• Absence of C=C stretching absorption around 1640 cm⁻¹: Rules out alkenes.

Based on these features, the compound is most likely an alcohol.

For a more precise identification, additional spectral data such as proton nuclear magnetic resonance (¹H NMR) and carbon-13 NMR (¹³C NMR) would be beneficial. These techniques provide further information about the molecular environment and connectivity of atoms within the compound.

In summary, by carefully analyzing the IR spectrum and considering the characteristic absorption bands of various functional groups, one can deduce the most probable structure of a compound with the molecular formula C₄H₈O.