Orgo 7 - 7. Haloalkanes (215-255) How Are Haloalkanes...

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7. Haloalkanes (215-255) How Are Haloalkanes Named? Compounds containing a halogen atom covalently bonded to an sp 3 hybridized carbon atom are named haloalkanes, or in the common system alkyl halides. The general symbol for an alkyl halide is R-X where X may be F, Cl, Br, or I. IUPAC names for haloalkanes are derived by naming the parent alkane according to rules previously learnt, locating and numbering the parent chain from the direction that gives the substituent encountered first the lower number. Show halogen substituents by prefixes and list them in alphabetical order along with other substituents. Use a number preceding the name to locate each halogen on the parent chain. In haloalkenes, the location of the double bond determines the numbering of the parent hydrocarbon. In molecules containing functional groups designated by a suffix, the location of the functional group indicated by the suffix determines the numbering. Common names of haloalkanes consist of the common name of the alkyl group followed by the name of the halide as a separate word. The name alkyl halide is a common name. several of the polyhalomethanes are common solvents and are referred to by their common or trivial names. Compounds of the type CHX 3 are called haloforms. The chloroflourocarbons (CFCs) manufactured under the trade name Freon are the most well known. CFCs are nontoxic, nonflammable, odorless, and noncorrosive. Characteristic Reactions of Haloalkanes A nucleophile (nucleus-loving reagenet) is any reagent that donates an unshared pair of electrons to form a new covalent bond. Nucleophilic substitution is any reaction in which one nucleophile is substituted for another. Substitution takes place on an sp 3 carbon, X is the leaving group and Nu - . Halide ions are among the best and most important leaving groups. Nucleophilic substitution occurs in the alkylation of an acetylide ion. Because all nucelophiles are also bases, nucleophilic substitution and base-promoted β -elimination are competing reactions. Nucleophilic substitution is a reaction in which one nucleophile is substituted for another. β -elimination reactions involve the removal of atoms or groups of atoms from two adjacent carbon atoms. Products of Nucleophilic Aliphatic Substitution Reactions If the Nu is negatively charged, then the atom donating the pair of electrons in the substitution reaction becomes neutral in the product. If the nucleophile is uncharged, then the atom donating the pair of electrons in the substitution reaction becomes positively charged in the product. The products then often undergo a second step involving proton transfer to yield a neutral substitution product. S N 2 and S N 1 Mechanisms for Nucleophilic Substitution In S N 2 bond breaking and bond formation occur simultaneously. The LGs departure is assisted by the incoming Nu. This is a bimolecular reaction, a reaction in which two species are involved in the reaction leading to the transition
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This note was uploaded on 02/09/2012 for the course SCIENCE 2213 taught by Professor Lee during the Spring '11 term at UWO.

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Orgo 7 - 7. Haloalkanes (215-255) How Are Haloalkanes...

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