Halocarbenes as diagnostic tools for mass spectral localization of double bonds

Abstract

Different halocyclopropanes prepared by cycloaddition of halocarbenes to olefins by phase-transfer reactions have been analyzed by gas chromatography/mass spectrometry (GUMS). Starting from CCI,-adducts, the investigations have been extended to bromine-and fluorine-containing cyclopropanes. As reaction partners, a group of olefins, containing different alkyl substituents, have been selected. Thereby, special attention has been paid to smooth reaction conditions, high reaction yield and simple handling. The suitability for mass spectral analysis is discussed. Fragmentation pathways and diagnostic potential are evaluated. Best results have been obtained by addition of bromofluorocarbene to double bonds. The resulting bromofluorocyclopropanes are considered to be the most promising derivatives for mass spectral localization of double bonds.

Fluorinated Carbenes

“…Scherch et al investigated the use of halocarbenes in cyclopropane reactions to fix the location of the double bonds. 378 In their study employing CBr 2 , CCl 2 , CF 2 , CClF, CHCl, CHF, and CBrF, they found that bromofluorocarbene was the most useful. This conclusion was based on the high reactivity of bromofluorocarbene coupled with the ease in identifying the adduct fragments due to its characteristic isotopic patterns.…”

“…Bis(trifluoromethyl)carbene ( 397) is a highly electrophilic species due to the two electron-withdrawing trifluoromethyl groups. Two useful precursors for its photochemical or thermal generation are bis(trifluoromethyl)diazomethane (375) and bis(trifluoromethyl)diazirine (378).…”

“…In mass spectral analysis using electron impact ionization, the location of double bonds in underivatized olefins often shifts, leading to ambiguous structural results. Scherch et al investigated the use of halocarbenes in cyclopropane reactions to fix the location of the double bonds . In their study employing CBr 2 , CCl 2 , CF 2 , CClF, CHCl, CHF, and CBrF, they found that bromofluorocarbene was the most useful.…”

Determination of Alkenes in Hydrocarbon Matrices by Acetone Chemical Ionization Mass Spectrometry

“…Chemical derivatization procedures that involve the conversion of structures containing double bonds to other chemical structures that retain their structural information upon analysis by mass spectrometry or other analytical techniques have been developed in the past. − However, these procedures are often time-consuming and cannot be easily implemented for the routine analysis of olefins. A faster and more sensitive approach is to selectively ionize the olefinic structures in the chemical ionization (CI) source of a mass spectrometer by ion−molecule reactions.…”