Types of Reaction Now Recognized

Both acetylenedicarboxylic acid and its ester undergo Michael addition reactions with a variety of nucleophilic reagents. An example is 

With Protons Provided by the Acetylene or Heterocyclic Reactant 

Pyrroles react at free a- or -positions with acetylenedicarboxylic acid or the methyl ester yielding mixtures of the corresponding maleic and fumaric acid derivatives. Protons are readily available to satisfy 

Acridine (9) combines readily with dimethyl acetylenedicarboxylate in methanol yielding the methoxide (11), which is in equilibrium with the corresponding 9-methoxy-9,10-dihydroacridine (12). Presumably the first formed zwitterion (10) abstracts a proton from the solvent, 

A small number of pyrroles undergo addition of acetylenedi-carboxylic acid across the 2,5-positions yielding adducts similar to those obtained from cyclopentadiene. In the case of 1-benzylpyrrole and the acid, some (13) is formed, probably through the intermediary of a species such as (8) a strong case has been made for the supposition that the Diels-Alder reaction occurs in two distinct stages, 

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Thermoplastic Polymers. Most thermoplastic polymers are used in high-volume, widely recognized applications, so they are often referred to as commodity plastics. (We will elaborate upon the distinction between a polymer and a plastic in Chapter 7, but for now we simply note that a plastic is a polymer that contains other additives and is usually identified by a variety of commercial trade names. There are numerous databases, both in books [1] and on the Internet [2], that can be used to identify the primary polymer components of most plastics. With a few notable exceptions, we will refer to most polymers by their generic chemical name.) The most common commodity thermoplastics are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS). These thermoplastics all have in common the general repeat unit -(CHX-CH2)-, where -X is -H for PE, -CH3 for PP, -Cl for PVC, and a benzene ring for PS. When we discuss polymerization reactions in Chapter 3, we will see that all of these thermoplastics can be produced by the same type of reaction. 

Ring closing and cross metathesis allow the rapid synthesis of simple cyclic and acyclic systems. The metathesis activity that is now possible using well-defined catalysts allows for the rapid generation of complexity from simple starting materials by relay processes and combinations of metathesis steps. Many of these reactions have been recognized only recently, are now beginning to be used in complex synthetic transformations. A few of these types of reactions will be outlined here to demonstrate the power of these multistep, relay processes. In these processes, an initial metathesis step leads to a new carbene that results in further transformations of the substrate. 

This type of reaction has been recognized in the decomposition of peroxi-dized linolenic acid. The application of olive oil to hasten the enlargement and maturation of fig fruits has been practiced predating Christianity, and it is now clear that this effect is due to the action of ethylene derived from the degradation of olive oil (Saad et al., 1969). Linolenic acid was once suggested as a precursor of ethylene, based on the observation that peroxidized... 

In your previous chemistry course, you classified reactions into four main types synthesis, decomposition, single displacement, and double displacement. You also learned to recognize combustion reactions and neutralization reactions. You have now learned to classify redox reactions. In addition, you have also learned about a special type of redox reaction known as a disproportionation reaction. 

In recent years, there has been a great deal of interest in the mechanisms of electron transfer processes.52-60 It is now recognized that oxidation-reduction reactions involving metal ions and their complexes are mainly of two types inner-sphere (ligand transfer) and outer-sphere (electron transfer) reactions. Prototypes of these two processes are represented by the following reactions. 

Photoisomerization of the diene (149) affords (150) by the now well-recognized reaction path for such sptecies. Another example of this type of cyclization has also been reported for the conversion of the diazepine (151) into the bicyclic comptound (152). ... 

Although a standard deviation of about 10% is now quite usual for rate constant measurements from fast-flow discharge and pulsed photolysis studies, it is still found that the same reaction studied in different laboratories by the same technique may give results of similar precision, but which differ by far more than would be expected on the basis of that precision. Potential sources of such discrepancies are many but, with experience, likely errors can sometimes be identified in particular cases. For example, reactions between short lived radical intermediates are common in combustion processes. The measurement of the rate constants of such reactions, where the reaction is second order with respect to the transient species, pose particular but well recognized difficulties stemming from the need to determine the absolute concentration of the reacting radical (Chapter 1). This is difficult to achieve and has been a common source of error in this type of determination as exemplified in the series of studies on the rate of the reaction CHO -I- CHO — CH2O -H CO. 

The conversion of one cyclopropenium ion into another, a substitution reaction, is gaining synthetic importance. Until recently, only nucleophilic substitution reactions of the nucleophilic addition-elimination type were known. However, three other processes are now recognized. These processes are ... 

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