Conjugated unsaturated systems

Conjugated unsaturated systems systems that have a p orbital on an atom... 

The new p orbital of the allyl radical is conjugated with those of the double bond => the allyl radical is a conjugated unsaturated system. 

Figure 13.3 The n molecular orbitals of the allyl cation. The allyl cation, like the allyl radical, is a conjugated unsaturated system. The shapes of molecular orbitals for the allyl cation calculated using quantum mechanical principles are shown alongside the schematic orbitals. 

The higher conjugated unsaturated systems will be mentioned later in connexion with the polyenes and the carotenoids (p. 233). 

We begin by bringing you up to speed on mechanisms and reminding you how to push electrons around with those curved arrows. We jog your memory with a discussion of substitution and elimination reactions and their mechanisms, in addition to free radical reactions. Next you review the structure, nomenclature, synthesis, and reactions of alcohols and ethers, and then you get to tackle conjugated unsaturated systems. Finally, we remind you of spectroscopic techniques, from the IR fingerprints to NMR shifts. The review in this part moves at a pretty fast pace, but we re sure you can keep up. 

Conjugated unsaturated systems cire an important part of organic chemistry, so in Chapter 4 we spend a little time talking about those systems, setting the stc e for our discussion of aromatic compounds that you can find in Chapter 6. 

Refresh your knowledge of key topics — from mechanisms to alcohol and ethers, from conjugated unsaturated systems to electrophiles and nucleophiles, getprepped for Organic II... 

In addition to the reactions mentioned, many other acetylenic compounds with a conjugated or non-conjugated unsaturated system have been carried out. The experimental procedures in this chapter are a selection of conversions which, in-our opinion, are relevant from a preparative point of view. 

Lycopene is a red pigment found in tomatoes, watermelon, papaya, guava, and pink grapefruit. An antioxidant like vitamin E, lycopene contains many conjugated double bonds—double bonds separated by only one single bond—that allow jt electron density to delocalize and give the molecule added stability. In Chapter 16 we learn about such conjugated unsaturated systems. 

Robinson, R. Extension of the theory of addition to conjugated unsaturated systems. II. The C-alkylation of certain derivatives of (i-aminocrotonic acid and the mechanism of the alkylation of ethyl acetoacetate and similar substances. J. Chem. Soc., Abstracts 1916,109, 1038-1046. 

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