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Phys Chem Chem Phys

Title:		Controlling factors of oligomerization at the water surface: why is isoprene such a unique VOC?
Author(s):		Ishizuka S; Fujii T; Matsugi A; Sakamoto Y; Hama T; Enami S;
Address:		"Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan"
Journal Title:		Phys Chem Chem Phys
Year:		2018
Volume:		20
Issue:		22
Page Number:		15400 - 15410
DOI:		10.1039/c8cp01551a
ISSN/ISBN:		1463-9084 (Electronic) 1463-9076 (Linking)
Abstract:		"Recent studies have shown that atmospheric particles are sufficiently acidic to enhance the uptake of unsaturated volatile organic compounds (VOCs) by triggering acid-catalyzed oligomerization. Controlling factors of oligomerization at the aqueous surfaces, however, remain to be elucidated. Herein, isoprene (2-methyl-1,3-butadiene, ISO), 1,3-butadiene (1,3-b), 1,4-pentadiene (1,4-p), 1-pentene (1-p), and 2-pentene (2-p) vapors are exposed to an acidic water microjet (1 > 1,3-b > 1,4-p >> 1-p approximately 2-p. Importantly, the cationic oligomerization of ISO yields a protonated decamer ((ISO)10H+, a C50 species of m/z 681.6), while the pentenes 1-p/2-p remain as protonated monomers. We suggest that ISO oligomerization is uniquely facilitated by (1) the resonance stabilization of (ISO)H+ through the formation of a tertiary carbocation with a conjugated C[double bond, length as m-dash]C bond pair, and (2) pi-electron enrichment induced by the neighboring methyl group. Experiments in D2O and D2O : H2O mixtures revealed that ISO oligomerization on the acidic water surface proceeds via two competitive mechanisms: chain-propagation and proton-exchange reactions. Furthermore, we found that ISO carbocations undergo addition to relatively inert 1-p, generating hitherto uncharacterized co-oligomers"
Keywords:
Notes:		"PubMed-not-MEDLINEIshizuka, Shinnosuke Fujii, Tomihide Matsugi, Akira Sakamoto, Yosuke Hama, Tetsuya Enami, Shinichi eng England 2018/05/26 Phys Chem Chem Phys. 2018 Jun 6; 20(22):15400-15410. doi: 10.1039/c8cp01551a"