Alkane loss

Nevertheless, alkane losses are analytically useful in distinguishing between isomeric C H2n+iNH3+ species. Thus, CH3CH2(CH3)CHNH3+ loses mainly C2IL and only a little CH4 (19 and 4%, respectively, of the base peak for NH3 loss), whereas... 

A closer look at the spectrum of K-decane also reveals fragment ions at m/z 84, 98, and 112, i.e., rearrangement ions at even mass number. The origin by loss of H from the accompanying carbenium ions at m/z 85, 99, and 113, respectively, can be excluded by application of the even-electron rule. Instead, alkane molecular ions may undergo alkane loss, [76] e.g.,... 

Veith, H.J. Gross, J.H. Alkane Loss From Collisionally Activated Alkylmethyle-neimmonium Ions. Org. Mass Spectrom. 1991,26, 1061-1064. 

The pattern of apparent alkane losses from specifically deuterated oarboxylate ions is most easily rationalized by invoking a 1,2-elimination mechanism (see Equation 1)... 

There has been considerable debate as to what degree Cl, like Br, radicals might play a role in Arctic springtime tropospheric chemistry. To obtain information on this, Jobson et al. (1994) collected daily air samples at Alert (82.5° N, 62.3° W) from January 21 to April 19, and on an ice floe 150 km north of Alert during April 2-15, 1992. They derived information on the concentrations of OH, Cl, and Br from the different decay rates of a suite of non-methane hydrocarbons the so-called hydrocarbon clock method. Besides some removal of alkanes by reaction with OH during ODEs, additional alkane losses, consistent with removal by reaction with Cl, were measured. 

The primary photochemical reaction is CO loss, and alkane loss occurs via secondary reactions ". Photoinduced rearrangement of the allyl complexes upon photolysis - ... 

Figure 6 Energy surface corresponding to an inverse KIE for alkane loss due to a single-step reductive elimination.

Two recent articles describe details of the isotope effects in C-H activation. One separates the kinetic isotope effect on reductive coupling from that of oxidative cleavage by looking at the irreversible loss of propane from Tp Rh(CNneopenyl)(/ -propyl)D/H. The oxidative cleavage isotope effect was measured by irreversible activation of CH2D2. These separate measurements were combined to give an overall inverse equilibrium isotope effect on alkane loss. ... 

The reactivity of doubly charged rare earth cations with small hydrocarbons was also investigated by FTICR-MS. In early studies, Freiser and coworkers examined reactions of Sc and Y " " (Hill et al., 1997), as well as La (Ranasinghe et al., 1992), with linear Cj-Cg alkanes combinations of electron transfer, hydride transfer, carbanion transfer, dehydrogenation, and alkane-loss products were observed. None of the metal ions reacted with methane, and La + was also unreactive with ethane. Since the metal dications have only one valence electron, oxidative addition to form two covalent bonds to the metal center is not possible, and alternative multicentered mechanisms were proposed. Another interesting aspect of these studies was the observation... 

Transposition of substituents takes place from aromatic compounds based on ortho effects from hydroxyphenyl ketones via assumed nucleophilic attack on the carbonyl carbon atom of the phenoxide site to give a tight tetravalent intermediate that promptly decomposes through benzyne neutral release and formation of a carboxylate anion (Scheme 17.19a). This reaction is hindered from meta- and para-substituted phenols. Alternatively, radical alkane loss is also observed that can be rationalized by considering the formation of an ion-neutral complex (Scheme 17.19b) comprised of quinone-like and alkylide groups. The relatively low ionization energy allows the generation of odd-electron quinone-like species and the elimination of the alkane radical (Scheme 17.19b). 

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