Alkyl Halides

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Overview:

Alkyl Halides introduces the structure of the halogenated hydrocarbons, their common uses, nomenclature, physical properties, preparations, and reactions. It is in this unit that the concept of devising syntheses is introduced.

Of the three types of alkyl halides to be studied, the aromatic and vinyl halides will be addressed in other units.

Common and systematic (usually IUPAC) nomenclature are addressed as well as commonly used names that do not necessarily fit a systematic form. Practice problems help clarify any unusual issues.

The uses and characteristics of selected alkyl halides such as Fluorocarbon 11, the trichloroethanes, and halothanes are specifically mentioned. The physical properties such as polarity, density, boiling points, and solubilities are addressed for the alkyl halides in general.

The Chemistry Professor consistently uses a highly effective format for presenting preparations and reactions of the alkyl halides and all other classes. This format includes addressing the general reaction, the mechanism, examples, and limitations. It is found that this consistent approach is most suitable for students who are unfamiliar with organic chemistry. This method of delivery helps reinforce the orderliness of the study.

Preparations addressed include preparations from alcohols, halogenation of hydrocarbons, addition of hydrogen halides to alkenes and alkynes, addition of halogens, allylic bromination, and halide exchange. The structures and mechanism for allylic bromination are addressed in detail. Both Markovnikov and anti-Markovnikov rules are considered. Few new mechanisms are presented in this unit, favoring approaching important mechanisms related to alkyl halides at a later time.

The reactions of alkyl halides presented include formation of alcohols, the Williamson ether synthesis, reaction with ammonia, the Wurtz reaction, dehydrohalogenation, and dehalogenation. The Saytzeff rule is stressed in applicable reactions.

In keeping with the philosophy used throughout her teaching career, the Chemistry Professor introduces a format for helping students understand the need to learn reactions and preparations: the synthesis. Students are asked to synthesize compounds, but the only starting materials they are given are alcohols of no more than 4 carbons, benzene, toluene, and inorganic reagents. Some very few, very specific organic reagents may be permitted under select circumstances, and those instances are very specifically defined. It seems that the thinking through of a synthesis employs a practice of logic that promotes understanding, rather than rote memorization. Further, the student experiences the need to exert care in selecting which reagent combinations to use in order to prevent undesirable side reactions. The expectation of devising syntheses is employed throughout the study of the remaining classes.

 

 

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