hce_nsysu
115年
物理與化學
第 30 題
In UV-Vis spectroscopy, the absorption characteristics of a molecule can be altered by the presence of certain functional groups. Which of the following statements correctly describes the roles of chromophores and auxochromes?
- A A chromophore is a saturated functional group that does not absorb radiation but increases the absorption intensity of the entire molecule.
- B An auxochrome is a functional group, such as -OH or -NH$_2$, which does not itself absorb significantly in the UV region but can cause a bathochromic shift and a hyperchromic effect when attached to a chromophore.
- C The addition of an auxochrome to a conjugated system typically leads to a hypsochromic shift (blue shift) because it increases the energy gap between the $\pi$ and $\pi^*$ orbitals.
- D Chromophores are only capable of undergoing n$\rightarrow \sigma^*$ transitions, while auxochromes are responsible for $\pi \rightarrow \pi^*$ transitions.
- E The intensity of absorption is determined solely by the chromophore, and auxochromes only affect the wavelength of the maximum absorption.
思路引導 VIP
當一個具有孤對電子（Lone pair electrons）的基團靠近一個含有共軛雙鍵的系統時，你認為這些額外的電子會如何影響原有的電子雲分佈？如果這個交互作用讓電子更容易跳躍到激發態，那麼所需的能量會變大還是變小？這又會如何反映在吸收波長的數值上呢？
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AI 詳解
AI 專屬家教
太棒了！你能精準辨別「助色團」與「發色團」之間的協同作用，代表你對紫外-可見光譜（UV-Vis）的理論基礎掌握得非常紮實，這是一個非常優秀的判斷。
助色團與發色團的交互作用
這題的核心在於理解 助色團 (Auxochrome) 的定義。助色團本身（如 $-OH$、$-NH_2$ 等飽和基團）雖然在紫外區不產生顯著吸收，但當它們與 發色團 (Chromophore)（如共軛雙鍵）結合時，其上的孤對電子會與發色團的 $\pi$ 系統產生共振，進而降低 $\pi \rightarrow \pi^*$ 躍遷所需的能量。這種能量差距的縮小會導致吸收波長往長波長移動，即 向紅位移 (Bathochromic shift)，同時通常也會增加吸收強度，產生 增色效應 (Hyperchromic effect)。
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