Step 1: Understanding the Concept:
UV absorbance in an organic molecule comes from its chromophore, the part of the structure with conjugated double bonds or aromatic rings that can absorb light in the ultraviolet range.
Step 2: Key Formula or Approach:
The more extended the conjugation in a chromophore, the longer the wavelength at which it absorbs (a bathochromic, or red, shift). So comparing candidate wavelengths means asking how conjugated morphine's aromatic system actually is.
Step 3: Detailed Explanation:
Morphine contains a phenolic aromatic ring fused into a partially unsaturated ring system, giving it more extended conjugation than a plain phenol or a simple benzene derivative. This extended conjugation lowers the energy gap for the electronic transition responsible for absorbance, which shows up as a shift to a longer wavelength compared to simpler aromatic compounds. Reported spectrophotometric data for morphine places this maximum near 286 nm, consistent with this level of conjugation.
Step 4: Final Answer:
Morphine shows its UV absorbance maximum at about 286 nm.