Charge-Site Initiation Inductive Cleavage

This reaction will not cleave a multiple bond to a heteroatom. For the carbonyl group (Equation 4.25), electron-pair attraction to the charge site yields the canonical resonance structure inductive cleavage of this then gives the alkyl ion and acyl radical. However, these products are the complements of the alkyl radical and acylium ion formed by a-cleavage (Equation 4.14), in contrast to the a- and i-reactions (Equations 4.13 and 4.22) at a saturated heteroatom. 

Considering Equations 4.14 and 4.25, one would expect aliphatic ketones to show four major ions from cleavage of the two bonds to the carbonyl group the favored acylium ion should be the one formed through loss of the larger alkyl group, and the favored carbonium ion should be the more stable one. Unknowns 4.9 and 4.10 are the spectra of 3-pentanone and 3-methyl-2-butanone which is which  

Even-electron ions. As discussed in Section 4.4, the favored decomposition of an EE ion yields another EE ion and a molecule as the neutral product. Product molecules of low proton affinity are favored, such as those of Equations 4.26-4.28 (PA = 7.4,6.2, and 7.2 eV, respectively Field s Rule, Section 4.4). Equations 4.26 and 4.27 are two-step pathways for forming the same products produced by Equations 4.22 and 4.25, respectively. However, these are energetically less favorable by 0.2-0.8 eV (20-80 kj/mol) than their one-step counterparts. 

In Unknown 4.11 the m/z 130 peak has the elemental composition CsHigO. Use the above mechanisms in elucidating the structure of this molecule. (Hint The molecular ion information from Table A.4 is also valuable.) 

The cleavage of two bonds in a ring is necessary to produce a fragment ion (Equation 4.30). Cleavage of one bond causes no change in mass, producing 

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C. Charge-Site-Initiated Cleavage Inductive Cleavage... 

Another common one-bond cleavage is charge-site-initiated or inductive cleavage, often indicated in a fragmentation mechanism by the symbol i. Inductive cleavage involves the attraction of an electron pair by an electronegative heteroatom that ends up as a radical or as a closed-shell neutral... 

One particularly intriguing aspect of Cl for molecular weight determination for polymers is the appearance of the quasimolecular ion (MH+). Cl leads to less fragmentation compared to EL Proton attachment preferentially occurs on heteroatoms, and the initial fragmentation is at the charge site normally by heterolytic cleavage (inductive effect). 

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