Colored Organic Compounds

Why are some organic compounds colored while others aren t Why is /3-carotene orange (the pigment in carrots), while benzene is colorless The answers involve both the structures of colored molecules and the way we perceive light. 

Ultraviolet spectrum of jS-carotenc, a conjugated molecule with 11 double bonds. The absorption occurs in the visible region. 

What is true for jS-carotene is also true for all other colored organic com pounds All have an extended system of tt electron conjugation that gives rise to an absorption in the visible region of the electromagnetic spectrum. 

Twenty-five years ago, someone interested in owning a computer would have paid approximately 150,000 for 16 megabytes of random-access memory that would have occupied a volume the size of a small desk. 

anyone can buy 16 MB of computer memory for under 50 and can fit the chips into their shirt pocket. The difference between then and now is due to improvements in photolithography, the process by which integrated circuit chips are made. 

Outline of the photolithography process for producing integrated circuit chips. 

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Parallel and side reactions occur resulting in undesired byproducts including dark-colored organic compounds take place, promoted by high temperatures and long reaction times (Table 7). 

Problem 12.47 Why do colored organic compounds, such as carotene (the orange pigment isolated from carrots), have extended conjugation ... 

The image is usually formed via photoelectrochemical deposition of metals (Pd, Ag, etc.). Metallic particles either directly form the image of a sufficient optical density (Goryachev et al, 1970, 1972) or serve as nuclei of crystallization in the course of development (Kelly and Vondeling, 1975). Photoelectrochemical reactions of colored organic compounds may also be employed for producing image (see, for example, Reichman et al, 1980). 

The presence of ji-ji or n-n conjugated systems does not assure absorption of visible light or generation of color. However, all colored organic compounds, including pigments, possess extended conjugated resonance systems. Thus, whereas 1,4-diphenylbutadiene is colorless. 1,6-diphenylhexatriene is colored. 

Key Mechanism 15-3 The Diels-Alder Reaction 684 15-12 The Diels-Alder as an Example of a Pericyclic Reaction 692 15-13 Ultraviolet Absorption Spectroscopy 696 15-14 Colored Organic Compounds 701... 

A new section, Colored Organic Compounds, has been added to explain how the HOMO-LUMO concept of highly conjugated molecules leads to absorption in the visible region, and how that applies to natural products, dyes, pH indicators, and food colors. 

The study of humic substances in water dates back to the Swedish scientist Berzelius, who investigated colored waters of a mineral spring. He later isolated colored organic compounds from swamp water and iron-containing... 

Colored organic compounds contain a chromophore, usually extended conjugation in the molecule. For example, 1,2-dibenzoylethylene (Experiments [3A] and [6]) is yellow 5-nitrosalicylic add (Experiment [29C]) is light yellow tetraphenylcyclopentadienone (Experiment [A3aD is purple. 

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