Reactions categorization

How fast is fast How slow is slow The previous discussion may he a bit confusing at this point in the book because specific examples of competing reactions will not be discussed until later chapters. However, it is important to know that when there are two competing reactions and one is slow and the other is fast, reaction time is an important parameter. Also, when there are two competing reactions, categorizing one as no reaction simply means that no product is expected from that reaction in the time frame specified. The term no reaction should provoke the question Is the reaction really impossible or just too slow to be observed ... 

As we move through the text, both fists will grow. For solving synthesis problems, it will be helpful to have the reactions categorized in this way in your mind. 

Traditionally one categorizes matter by phases such as gases, liquids and solids. Chemistry is usually concerned with matter m the gas and liquid phases, whereas physics is concerned with the solid phase. However, this distinction is not well defined often chemists are concerned with the solid state and reactions between solid-state phases, and physicists often study atoms and molecular systems in the gas phase. The tenn condensed phases usually encompasses both the liquid state and the solid state, but not the gas state. In this section, the emphasis will be placed on the solid state with a brief discussion of liquids. 

The material in the succeeding chapters describes both the synthesis of the indole ring and means of substituent modification which are especially important in indole chemistry. The first seven chapters describe the preparation of indoles from benzenoid precursors. Chapter 8 describes preparation of indoles from pyrroles by annelation reactions. These syntheses can be categorized by using the concept of bond disconnection to specify the bond(s) formed in the synthesis. The categories are indicated by the number and identity of the bond(s) formed. This classification is given in Scheme 1.1. 

Chemical Properties. Reactions of quaternaries can be categorized iato three types (169) Hoffman eliminations, displacements, and rearrangements. Thermal decomposition of a quaternary ammonium hydroxide to an alkene, tertiary amine, and water is known as the Hoffman elimination (eq. la) (170). This reaction has not been used extensively to prepare olefins. Some cycHc olefins, however, are best prepared this way (171). Exhaustive methylation, followed by elimination, is known as the Hoffman degradation and is important ia the stmctural determination of unknown amines, especially for alkaloids (qv) (172). 

Liquid Compositions. Urea—formaldehyde reaction products also are available commercially as Hquids that can be categorized into two classes, ie, water suspensions and water solutions. 

Various processes can be employed to manufacture urea—formaldehyde products. They are generally categorized into two types, ie, dilute solution processes and concentrated solution processes. Table 3 Hsts select U.S. manufacturers of UF reaction products and their products. 

Tliis categor> includes chemicals reacting vitli otlier chemicals or materials and tlie decomposition of unstable chemicals (e.g tlie reaction of some substances witli water or moist air or witli strong oxidizing and reducing agents). 

The fluorination reactions considered so far can be categorized as metathesis, oxidation or substitution, Occasionally reductive fluorination is the preferred route to a lower fluoride. Examples are ... 

Although the first ionic liquid expressly categorized as being task-specific featured the incorporation of the function within the cation core, subsequent research has focused on the incorporation of functionality into a branch appended to the cation [11]. In this fashion, a number of task-specific ionic liquids built up from 1-methyl- and 1-butylimidazole have been prepared, produced by means of the reaction between these imidazoles and haloalkanes also incorporating a desired functional group (Scheme 2.3-1). Bazureau has used this approach to prepare imida-... 

Thermal and photochemical cycloaddition reactions always take place with opposite stereochemistry. As with electrocyclic reactions, we can categorize cycloadditions according to the total number of electron pairs (double bonds) involved in the rearrangement. Thus, a thermal Diels-Alder [4 + 2] reaction between a diene and a dienophile involves an odd number (three) of electron pairs and takes place by a suprafacial pathway. A thermal [2 + 2] reaction between two alkenes involves an even number (two) of electron pairs and must take place by an antarafacial pathway. For photochemical cyclizations, these selectivities are reversed. The general rules are given in Table 30.2. 

It was a common belief that all phenomena of bioluminescence were caused by the luciferin-luciferase reaction until the biolumines-cent protein aequorin was discovered in 1962 (Shimomura et al., 1962). When the terms luciferin and luciferase were found to be unsuitable for categorizing the two bioluminescent proteins, aequorin and another from the tubeworm Chaetopterus, a new term photoprotein was introduced to supplement the term luciferin (Shimomura and Johnson, 1966). Further explanations for the terms luciferin and photoprotein are given below. 

This reaction may be followed by others (complex formation and/or precipitation) which are independent of the electrode potential but determined by the nature and concentration of the electrolyte. It is impossible to discuss all the problems relating to zinc electrodes without looking at the electrolyte system and the kind of cell operation (primary or rechargeable). The only way to cover all the possible combinations is by another mode of characterization or categorization, which is used in the subsequent sections ... 

Seizure disorders are generally categorized as idiopathic or acquired. Idiopathic seizures have no known cause acquired seizure disorders have a known cause, including high fever, electrolyte imbalances, uremia, hypoglycemia, hypoxia, brain tumors, and some drug withdrawal reactions. Once the cause is removed (if it can be removed), the seizures theoretically cease. 

Reaction of sulfones with nucleophiles has been studied a great deal from both a preparative and a mechanistic standpoint1,2- The nucleophilic substitution reactions of sulfones may be categorized to four groups according to the sites attacked by the nucleophile (equation 1). 

Many literature preparations of difunctional compounds are extensions of the methods applicable to monofunctional compounds. As an example, the reaction RCI — ROH might be used for the preparation of diols from an appropriate dichloro compund. Such methods are difficult to categorize and may be found in either the monofunctional or difunctional sections, depending on the focus of the original paper. 

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