The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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The allenes are a group of hydrocarbons with the general formula of CnH2n 2, but they differ from the alkynes in that there are two double bonds present, involving three carbon atoms, instead of the triple bond with two carbon atoms found in the alkynes. The functional group of the allenes is this twin double bond. All allenes are derivatives from 1,2 propadiene (allene) and they are isomers (compounds with the same chemical formulas but different structures and properties) of alkynes. Lower allenes are all liquids with a characteristic odor, and the higher members of the series are solids.
The allenes are not generally as stable as the alkenes which have only one double bond. Allenes can usually be converted to the appropriate alkyne by the simple addition of a base. Allenes are prepared by the removal of bromine and hydrogen bromide from 1,2,3 tribromopropane and its derivatives under the action of potassium hydroxide, zinc, and ethanol. The reactions which allenes partake in are typical of the alkenes, generally addition reactions involving the breaking down of the double bonds that are present.
Although allenes are far less common in nature than alkenes, a number of naturally occurring allenes have been identified and described, including pyrethrolone (an insecticide) and mycomycin (an antibiotic).