Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

16. Conjugated Systems

Conjugation Chemistry

Organic Chemistry

16. Conjugated Systems

Conjugation Chemistry

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3:05 minutes

Problem 40d,e,f

Textbook Question

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.
(d)
(e)
(f)

Verified step by step guidance

Step 1: Analyze the structures provided in the image. For a compound to be colored, it typically needs an extended conjugation system (a series of alternating single and double bonds) and the ability to absorb visible light. This is often associated with π-electron delocalization over a large portion of the molecule.

Step 2: For structure (i), observe the presence of an azo group (-N=N-) connecting two aromatic rings. Azo compounds are often colored due to their extended conjugation system. Mark the continuous sp2 hybridized atoms starting from one aromatic ring, through the azo group, and into the second aromatic ring.

Step 3: For structure (ii), note the presence of a fused aromatic system (chromophore) and substituents like methoxy (-OCH3) and dimethylamino (-N(CH3)2) groups. These groups can act as auxochromes, enhancing the molecule's ability to absorb visible light. Mark the extended conjugation system across the fused aromatic rings and the carbonyl group.

Step 4: For structure (iii), examine the aromatic rings and the ketone group. While there is conjugation within the individual aromatic rings, the conjugation does not extend across the entire molecule due to the lack of connectivity between the rings. This structure is less likely to be colored.

Step 5: Summarize the findings: (i) and (ii) are likely to be colored due to their extended conjugation systems, while (iii) is less likely to be colored. Ensure the extended conjugation is marked appropriately for (i) and (ii).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conjugation

Conjugation refers to the overlap of p-orbitals across adjacent sp2 hybridized atoms, allowing for the delocalization of π electrons. This delocalization stabilizes the molecule and can lead to color in organic compounds, as it lowers the energy gap between electronic states, allowing for visible light absorption.

Color in Organic Compounds

The color of organic compounds is often due to the presence of conjugated systems, where the extended π-electron system can absorb specific wavelengths of light. Compounds with longer conjugated systems typically absorb light in the visible spectrum, resulting in color, while those with shorter systems may appear colorless.

Hybridization and Molecular Geometry

Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals, which influences the geometry and bonding of molecules. In organic chemistry, sp2 hybridization is common in alkenes and aromatic compounds, leading to planar structures that facilitate conjugation and affect the compound's electronic properties.

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Related Practice

Textbook Question

Identify the following dienes as being in the s-cis or s-trans conformation. If they are in the s-trans conformation, draw them in the s-cis conformation. [It may not always be possible.]

(c)

Textbook Question

Identify the following dienes as being in the s-cis or s-trans conformation. If they are in the s-trans conformation, draw them in the s-cis conformation. [It may not always be possible.]

(e)

Textbook Question

At pH = 7, one of the ions shown here is purple and the other is blue. Which is which?

Textbook Question

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(a)

(b)

(c)

Textbook Question

How can you use UV spectroscopy to distinguish between the compounds in each of the following pairs?

Textbook Question

How can you use UV spectroscopy to distinguish between the compounds in each of the following pairs?

Textbook Question

One milligram of a compound of molecular weight 160 is dissolved in 10 mL of ethanol, and the solution is poured into a 1-cm UV cell. The UV spectrum is taken, and there is an absorption at λ_max = 247 nm. The maximum absorbance at 247 nm is 0.50. Calculate the value of e for this absorption.

Textbook Question

The UV spectrum of 1-phenylprop-2-en-1-ol shows an intense absorption at 220 nm and a weaker absorption at 258 nm. When this compound is treated with dilute sulfuric acid, it rearranges to an isomer with an intense absorption at 250 nm and a weaker absorption at 290 nm. Suggest a structure for the isomeric product and propose a mechanism for its formation.

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Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp2 hybridized atoms.(d) (e) (f)

Key Concepts

Conjugation

Color in Organic Compounds

Hybridization and Molecular Geometry

Watch next

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.
(d)
(e)
(f)