Cycloheptanone 1 - -1 -alkene

Cycloheptanone (49) contained a carbonyl and the analysis treated that carbon as C OC where did the second oxygen come from Multiply bonded atoms such as this are found in alkenes, alkynes, carbonyls, and nitriles and they require yet another rule. 

General Preparations.—Alkenes. Dehalogenation of vicinal dihalides is easily carried out using sodium in liquid ammonia, e.g. 1,2-dichlorocyclo-octane gave ds-cyclo-octene in 95% yield.The scope of the synthesis of ap-unsaturated carbonyl compounds by syn-elimination from 2-phenylselenoxides has been studied only low yields of the desired ketone were obtained from 2-phenylseleno-cycloheptanone and cyclo-octanone because of the competing Pummerer rearrangements, but improved yields could be obtained by prior conversion of the ketones into ketals. The reaction worked well for 2-methoxycarbonyl cyclic ketones, e.g. 2-methoxycarbonylcyclo-oct-2-en-l-one was prepared in 93% yield. ... 

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