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Although processes for the production of LVOC are extremely diverse and complex, they are typically composed of a combination of simpler activities and equipment that are based on similar scientific and engineering principles. Chapter 2 describes how unit processes, unit operations, site infrastructure, energy control and management systems are combined and modified to create a production sequence for the desired LVOC product. Most LVOC processes can be described in terms of five distinct steps, namely: raw material supply / work-up, synthesis, product separation / refining, product handling / storage, and emission abatement | MODULE 6 ORGANIC CHEMISTRY REACTION MECHANISMS O3.1 Acids and Bases O3.2 Carbanion Attack at a Carbonyl Group O3.3 The Mechanism of Reduction Reactions O3.4 Nucleophilic Attack by Water O3.5 Nucleophilic Attack by an Alcohol O3.6 Addition Elimination Reactions of Carboxylic Acid Derivatives O3.7 Free Radical Reactions O3.8 Bimolecular Nucleophilic Substitution or SN2 Reactions O3.9 Unimolecular Nucleophilic Substitution or SN1 Reactions O3.10 Elimination Reactions O3.11 Substitution versus Elimination Reactions O3.1 ACIDS AND BASES As noted in Section 11.1 for more than 300 years chemists have classified substances that behave like vinegar as acids while those that have properties like the ash from a wood fire have been called alkalies or bases. Today when chemists use the words acid or base they refer to a model developed independently by Br0nsted Lowry and Bjerrum. Since the most explicit statement of this theory was contained in the writings of Br0nsted it is most commonly known as the Br0nsted acid-base theory. Br0nsted Acid-Base Theory Br0nsted argued that all acid-base reactions involve the transfer of an H ion or proton. Water reacts with itself for example by transferring an H ion from one molecule to another to form an H3O ion and an OH ion. H2O H2O -- H3O OH I_I r t -H 1 2 ORGANIC REACTION MECHANISMS According to the theory a Bronsted acid is a proton donor and a Bronsted base is a proton acceptor. Acids are often divided into categories such as strong and weak. One measure of the strength of an acid is the acid dissociation equilibrium constant Ka for that acid. K HO - A I Ka HA When Ka is relatively large we have a strong acid. HCl Ka 1 X 106 When it is small we have a weak acid. CH3CO2H Ka 1.8 X 10 5 When it is very small we have a very weak acid. H2O Ka 1.8 X 10 16 In 1909 S. P. L. S0renson suggested that the enormous range of concentrations of the H3O and OH ions in aqueous solutions could be compressed into a more manageable set of data
