Final answer:
Major peaks above 1580 cm⁻¹ in an IR spectrum are assigned by identifying the characteristic absorption frequencies of functional groups, with a common peak around 2900-3000 cm⁻¹ for tetrahedral carbon-hydrogen bonds.
Step-by-step explanation:
Assigning the major peaks above 1580 cm⁻¹ in a spectrum involves identifying the functional groups present within a molecule based on their characteristic absorption frequencies. For example, the jagged peak around 2900-3000 cm⁻¹ is indicative of tetrahedral carbon-hydrogen bonds, commonly found in organic molecules. While this peak isn't very diagnostic due to its prevalence, it does provide a reference point within the spectrum.
Other functional groups exhibit more distinct peaks, which can be identified by consulting a reference table, such as those provided in spectroscopy textbooks or online databases, which summarize the absorption frequencies for different functional groups. Assigning peaks is a crucial step in infrared (IR) spectroscopy, where transmittance is measured at various wavenumbers, with peaks indicating strong absorption by specific molecular bonds.