QQuestionChemistry
QuestionChemistry
The Diels-Alder reaction is a concerted reaction; this means:
a) the reaction is highly endothermic
b) the products contain rings
c) the reaction folows Markovnikov's rule
d) a mixture of endo and exo products are formed
e) all bond making and bond breaking occurs simultaneously
2) Which of the following compounds absorbs the longest wavelength of UV-visible light?
a) (E)-but- 2 -ene
b) (Z)- 1,3 -hexadiene
c) (E)- 1,3.5 -hexatriene
d) (Z)-but-ene
e) hex- 1 -ene
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Answer
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Step 1:I'll solve this problem step by step, focusing on the UV-visible light absorption characteristics of these compounds.
Step 2:: Understand the Factors Affecting UV-Visible Light Absorption
The wavelength of UV-visible light absorption depends on the conjugation and electron delocalization in the molecule. Key factors include: - Number of conjugated double bonds - Geometry of the conjugated system - Electron density in the π system
Step 3:: Analyze the Conjugation in Each Molecule
e) Hex-1-ene: $$CH_{2}=CH-CH_{2}-CH_{2}-CH_{2}-CH_{3}
- 1 double bond - Limited conjugation - Minimal electron delocalization - 2 conjugated double bonds - Allows more electron delocalization - Potential for longer wavelength absorption - 3 conjugated double bonds - Extensive electron delocalization - Longest potential conjugation - Identical to (E)-but- 2 -ene - 1 double bond - Limited conjugation - 1 isolated double bond - No conjugation - Shortest wavelength absorption
Step 4:: Determine the Wavelength of Absorption
The more conjugated the system, the longer the wavelength of absorbed light. - Ranking from longest to shortest wavelength:
Step 5:(E)- 1,3,5 -hexatriene
Step 6:(Z)- 1,3 -hexadiene
Step 7:(Z)-but- 2 -ene
Step 8:(E)-but- 2 -ene
Step 9:
Hex- 1 -ene
Final Answer
c) (E)- 1,3,5 -hexatriene will absorb the longest wavelength of UV-visible light due to its extensive conjugation of three double bonds.
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