Bonding conjugated dienes

As we saw in Chapter 5 dehydrations and dehydrohalogenations are typically regiose lective m the direction that leads to the most stable double bond Conjugated dienes are more stable than isolated dienes and are formed faster via a lower energy transition state... 

Telomerization is the reaction of olefins having conjugated double bonds (conjugated dienes) in the presence of a nucleophile (telogen). The main... 

The products derived from intermolecular cycloaddition of sydnones readily lose carbon dioxide. If the original cycloaddition is carried out on a diene, the resulting azomethine imine intermediate can be trapped intramolecularly. Thus, 1,5-cyclooctadiene cycloadded to a sydnone to afford the cycloadduct (168).78b It is theorized that the intermolecular monocycloadduct (169) was formed, lost carbon dioxide, and cycloadded as a cyclic azomethine imine to the remaining C—C double bond. Conjugated dienes have been shown to undergo a similar sequence.87... 

In the remainder of Chapter 16 we examine conjugated dienes, compounds having two double bonds joined by one o bond. Conjugated dienes are also called 1,3-dienes. 1,3-Butadiene (CH2=CH-CH=CH2) is the simplest conjugated diene. 

Conjugated diene (Section 16.1 A) A compound that contains two carbon-carbon double bonds joined by a single G bond. Pi (jt) electrons are delocalized over both double bonds. Conjugated dienes are also called 1,3-dienes. 

Two Neighboring Double Bonds Conjugated Dienes CHAPTER 14... 

Does the structure of conjugated dienes affect their reactivity Although more stable thermodynamically than dienes with isolated double bonds, conjugated dienes are actually more reactive kinetically in the presence of electrophiles and other reagents. 1,3-Butadiene, for example, readily adds 1 mol of cold hydrogen bromide. Two isomeric addition products are formed 3-bromo-1-butene and l-bromo-2-butene. 

Isolated dienes have two double bonds separated by two or more a bonds. Conjugated dienes have two double bonds separated by only one a bond. 

One a bond separates two double bonds = conjugated diene... 

Double bonds separated by one a bond = conjugated diene smaller heat of hydrogenation... 

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