Five compounds are shown for each of the IR spectra below. Indicate which of the five compounds is responsible for each spectrum.
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Verified step by step guidance

1. Step 1: Analyze the IR spectrum provided. The spectrum shows a strong absorption around 1700 cm⁻¹, which is characteristic of a carbonyl (C=O) functional group. This indicates the presence of a compound with a ketone, aldehyde, or similar carbonyl-containing functional group.
2. Step 2: Look for additional peaks in the spectrum. There is a broad absorption around 3000 cm⁻¹, which corresponds to C-H stretching vibrations. This suggests the compound contains alkyl or aromatic groups.
3. Step 3: Compare the IR spectrum with the provided compounds. Compound (i) contains a ketone group (C=O) and alkyl groups, which matches the strong absorption at 1700 cm⁻¹ and the C-H stretching around 3000 cm⁻¹. Compound (ii) also contains a carbonyl group, but it is part of an aldehyde, which would typically show a distinct peak around 2700 cm⁻¹ for the aldehyde C-H stretch, not observed here.
4. Step 4: Eliminate compounds that do not match the spectrum. Compound (iii) contains a nitrile group (C≡N), which would show a sharp peak around 2200 cm⁻¹, not present in the spectrum. Compound (iv) contains an alcohol group (-OH), which would show a broad peak around 3200-3600 cm⁻¹, also not observed.
5. Step 5: Based on the analysis, compound (i) is the most likely match for the IR spectrum, as its functional groups and structure align with the observed peaks.

Key Concepts

Infrared Spectroscopy (IR)

Infrared spectroscopy is an analytical technique used to identify molecular structures based on the absorption of infrared light by a sample. Different functional groups absorb characteristic wavelengths of IR radiation, leading to distinct peaks in the spectrum. By analyzing these peaks, chemists can deduce the presence of specific bonds and functional groups in a compound.

Wavenumbers and Transmittance

In IR spectroscopy, wavenumbers (measured in cm⁻¹) represent the frequency of the absorbed light, while transmittance indicates the amount of light that passes through the sample. Peaks in the spectrum correspond to specific wavenumbers where absorption occurs, indicating the presence of certain functional groups. A lower transmittance value at a given wavenumber signifies stronger absorption.

Functional Group Identification

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In IR spectroscopy, each functional group has a unique absorption pattern, allowing chemists to identify them based on the spectrum. For example, O-H bonds typically show strong absorption around 3200-3600 cm⁻¹, while C=O bonds appear around 1700 cm⁻¹.