A photoionization study of the ion-neutral complexes CH3CH+CH3·CH2CH3] and CH3CH2CH+CH3·CH3in the gas phase: Formation, H-transfer and C—C bond formation between partners, and channeling of energy into dissociation

✍ Scribed by John C. Traeger; Charles E. Hudson; David J. McAdoo

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 910 KB
• Volume: 7
• Category: Article
• ISSN: 1044-0305
• DOI: 10.1016/1044-0305(95)00591-9

✦ Synopsis

Photoionization

mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the Iz-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex [CHaCH+CHa'CH,CH,] (31, but not through [CH,CH+CH,CH,'CH,] (4). The appearance energy for C,H, + formation from 1 is 66 kJ mol-' below that ex ected P for the formation of n-C,H: and just above that expected for formation of I'-C,H,. This demonstrates that the H shift that isomerizes C,H: is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 + CH,CH+CH,CHs +' CH, by direct cleavage of the Cl -C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 + 2 + 4 --, C,H, '+ CH, occurs in this same energy range. Thus some of the potential energy made available by the isomerization of ?z-C,H, in 1 is specifically channeled into the coordinate for dissociation.

In contrast, analogous formation of 3 by 1 + 3 is predominantly followed by reaction between the electrostatically bound partners. (