Rank each set of compounds in order of decreasing λ_max:
a.

검증된 단계별 안내

Step 1: Understand the concept of λmax (maximum wavelength of absorption). λmax is influenced by the extent of conjugation in a molecule. Greater conjugation leads to a longer λmax because the energy gap between the HOMO and LUMO decreases.

Step 2: Analyze the conjugation in each compound. Compound A has two benzene rings connected directly, providing significant conjugation. Compound B has a benzene ring conjugated with an alkene group, which is less conjugated than A. Compound C has a single benzene ring with no extended conjugation. Compound D has three conjugated systems (two benzene rings and an alkene), making it the most conjugated.

Step 3: Rank the compounds based on their conjugation. Compound D has the most conjugation, followed by A, then B, and finally C.

Step 4: Explain why conjugation affects λmax. Conjugation allows delocalization of π-electrons, reducing the energy required for electronic transitions and increasing the wavelength of absorption.

Step 5: Final ranking in order of decreasing λmax: D > A > B > C.

비슷한 문제에 대한 검증된 영상 답변:

이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Conjugation

Conjugation refers to the overlap of p-orbitals across adjacent double bonds or between double bonds and lone pairs, allowing for delocalization of electrons. This delocalization lowers the energy of the molecule and can lead to increased stability and extended π-systems, which typically results in a higher λmax (lmax) in UV-Vis spectroscopy.

Aromaticity

Aromatic compounds are cyclic, planar structures with a ring of resonance that follow Hückel's rule (4n + 2 π electrons). Aromaticity contributes to the stability of the compound and can influence the absorption of light, often resulting in a higher λmax due to the increased electron delocalization within the aromatic system.

Substituent Effects

The presence of different substituents on a benzene ring can significantly affect the electronic properties of the compound. Electron-donating groups (EDGs) can increase the electron density and enhance conjugation, leading to a higher λmax, while electron-withdrawing groups (EWGs) can decrease electron density and lower λmax. Understanding these effects is crucial for ranking the compounds based on their lmax.

Rank each set of compounds in order of decreasing λmax:a.