Final answer:
Characteristic frequencies of benzene derivatives in IR spectroscopy are unique for each functional group, such as the aromatic C-H stretch around 3100-3000 cm-1 and the carbonyl group near 1700 cm-1. Additional substituents, like a nitro group, introduce more absorption bands. The fingerprint region (400-1400 cm-1) offers a unique pattern aiding in compound identification.
Step-by-step explanation:
Characteristic Frequencies of Benzene Derivatives in IR Spectroscopy
In infrared (IR) spectroscopy, different functional groups absorb characteristic frequencies of IR radiation. For benzene derivatives, these characteristic frequencies manifest in absorption bands that are indicative of particular bond vibrations. The aromatic C-H stretch in benzene appears typically around 3100-3000 cm-1. Substituents on the benzene ring can shift this absorption and can also introduce additional bands. For example, a nitro group shows strong peaks around 1525 and 1350 cm-1 due to the symmetric and asymmetric stretching of the N-O bond. The carbonyl group (C=O), which isn't present in benzene itself but is common in its derivatives such as acetophenone, shows a strong absorption near 1700 cm-1. Comparing IR spectra of unknown samples to known spectra can help identify specific compounds.
Exercise activities, such as using the online Spectral Database for Organic Compounds, enable students to practice identifying these characteristic IR absorbance bands, further reinforcing their understanding of molecular structure and IR spectroscopy.
It's important to note the fingerprint region of the IR spectrum (400-1400 cm-1), which provides a unique pattern for each molecule and can be crucial in compound identification.
In summary, recognizing the trend in wavelengths of C-C single, double, and triple bonds relates to the idea that chemical bonds can be thought of as springs with varying stiffness, which affects the frequency at which they vibrate.