2-Bromoethyl nitrite

These values were obtained in the presence of 2-bromoethyl nitrite. 

Iglesias, E., Leis, J.R., Pena, M.E. Micellar effects on the nitrosation of piperidines by 2-bromoethyl nitrite and 1-phenylethyl nitrite in basic media. Langmuir 1994, 10(3), 662-669. 

Cations react rapidly and indiscriminately with nucleophiles. Thus if a reaction which is suspected to go via a cationic intermediate is carried out in the presence of an added nucleophile, and an adduct containing the new nucleophile is obtained, this provides evidence for a cationic intermediate which is trapped by the added nucleophile. For example, the addition of bromine to alkenes is thought to go via a cationic intermediate 4 (reaction 5.11). If chloride or nitrite ions are added to the reaction mixture, the chloride or nitrite adducts 5 and 6 are obtained, even though the chloride and nitrite ions do not react with ethene (or 1,2-dibromoethane) directly at a rate that would account for the amount of these products in the reaction mixture. This provides strong evidence for the intermediate bromoethyl cation 4, which will be trapped by the added chloride or nitrite ions (reactions 5.12 and 5.13). The structure of bromoalkyl cations is discussed further in the section on electrophilic addition. 

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