Final answer:
In the experiment, the absorbance of NADH at 340 nm is used to determine the rate at which a carbonyl-based compound is formed from an alcohol, as NADH is produced alongside the desired product and has a unique absorbance at this wavelength that can be measured over time.
Step-by-step explanation:
In the given experiment, the formation of a carbonyl-based compound from an alcohol is monitored not by the direct absorbance of alcohol or carbonyl compound, but by tracking an intermediate or side-product. Specifically, the absorbance of NADH at 340 nm is being used to determine the rate of the reaction. NADH has a distinct absorbance at this wavelength, allowing for its concentration to be measured over time. This concentration change is directly related to the progress of the reaction, as NADH is a product of the enzymatic reduction that often accompanies the oxidation of alcohols to carbonyl compounds in biochemical assays.
The observation that different functional groups, such as the carbonyl group, absorb infrared light at different characteristic frequencies enables us to use infrared spectroscopy as a powerful identification tool. However, in this specific experiment, NADH is used because its absorbance is easier to monitor continuously, providing a real-time measure of the reaction's progression.