The IR spectrum of an organic compound gives us information about

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Question restatement: The IR spectrum of an organic compound gives us information about
Options:
a. the number of carbons atom in the molecule.
b. the empirical formula of the compound.
c. the molecular mass of the compound.
d. the functional groups present in the compound.

Option a: 'the number of carbons atom in the molecule.' Infrared spectroscopy does not provide exact counts of atoms or the overall carbon skeleton. It is primarily sensitive to vibrations of chemical bonds and functional groups, not precise atomic counts, so this statement misrepresents the capability of IR.

Option b: 'the empirical formula of the compound.' While empirical formula gives a rough idea of elemental composition, IR spectra do not directly yield empirical formulas. They do not provide percentages or ratios of elements; they reveal which bonds and functional groups are present, not an exact elemental formula.

Option c: 'the molecular mass of the compound.' Molecular mass is typically determined by methods like mass spectrometry or large-scale molecular weight calculations, not by IR spectroscopy. IR analyzes vibrational transitions, not mass, so this is inaccurate.

Option d: 'the functional groups present in the compound.' This aligns with the core function of IR spectroscopy: detecting characteristic vibrational frequencies associated with specific bonds (e.g., O–H, C=O, C–H, N–H, etc.). By examining peak positions and intensities, one can infer which functional groups are present, making this option true in the context of IR analysis.

Why the other options are flawed: The invalid choices either claim capabilities IR does not provide (exact atom counts, empirical formulas, or molecular mass) or misrepresent the interpretive focus of IR as a tool for bonding environments rather than exact quantitative composition. The diagnostic power of IR lies in identifying functional groups through bond-specific vibrational patterns, not in delivering precise molecular formulas, masses, or skeletal counts.

In summary, the correct interpretation of an IR spectrum is its ability to indicate which functional groups are present in the compound, based on characteristic absorption bands associated with particular bonds and functional groups.

MUF0042 Chemistry Unit 2 - Semester 2, 2025 8.12 Quiz: IR Spectroscopy

The IR spectrum of an organic compound gives us information about

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