This overview compiles the actual knowledge of the biogenic emissions of some volatile organic compounds (VOCs), i.e., isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls, and acids. We discuss VOC biosynthesis, emission inventories, relations between emission and plant physiology as well as temperature and radiation, and ecophysiological functions. For isoprene and monoterpenes, an extended summary of standard emission factors, with data related to the plant genus and species, is included. The data compilation shows that we have quite a substantial knowledge of the emission of isoprene and monoterpenes, including emission rates, emission regulation, and biosynthesis. The situation is worse in the case of numerous other compounds (other VOCs or OVOCs) being emitted by the biosphere. This is reflected in the insufficient knowledge of emission rates and biological functions. Except for the terpenoids, only a limited number of studies of OVOCs are available; data are summarized for alkanes, alkenes, carbonyls, alcohols, acids, and esters. In addition to closing these gaps of knowledge, one of the major objectives for future VOC research is improving our knowledge of the fate of organic carbon in the atmosphere, ending up in oxidation products and/or as aerosol particles.

Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology

The silanol group and its role in liquid chromatography

Silicon-supported alkylsiloxane layers were prepared by reaction of alkylmethyldichlorosilanes and alkyltrichlorosilanes with silicon wafers under two conditions:  (1) in the vapor phase and (2) in toluene in the presence of ethyldiisopropylamine. Covalent attachment of di- and trichlorosilanes to the surface of silicon/silicon oxide through SiS−O−Si bonds occurs for the amine-catalyzed reactions. This sets apart this reaction from the self-assembly process that occurs in the reaction between certain trichlorosilanes and hydrated silica with no amine present. The thickness of the layers formed from dichloro- and trichlorosilanes (as assessed by ellipsometry) is on the order of the single molecule sizes and increases gradually with alkyl chain length. The thickness values are considerably smaller (by a factor of ∼0.75) than the length of the fully stretched alkyl chain, which argues for disordered structures of the monolayers. Dynamic advancing and receding contact angles for water, methylene iodide, and h...

Self-Assembly Is Not the Only Reaction Possible between Alkyltrichlorosilanes and Surfaces: Monomolecular and Oligomeric Covalently Attached Layers of Dichloro- and Trichloroalkylsilanes on Silicon

Chemically grafted monolayers of trialkylsilanes were prepared by reaction of (primarily) alkyldimethylchlorosilanes with silicon wafers under three conditions:  in the vapor phase at elevated temperature (60−70 °C), in toluene in the presence of ethyldiisopropylamine (EDIPA) at room temperature, in toluene/EDIPA at 60−70 °C. It was determined that reactions at the solution−solid interface are very slow in the later stages of the reaction and that long reaction times are necessary to achieve maximum bonding density. The bonding density is determined and can be controlled by the reaction conditions. The highest carbon content on the surface (assessed by X-ray photoelectron spectroscopy) as well as the highest contact angles were obtained using vapor phase reactions. A series of nine H(CH2)nMe2Si− surfaces was prepared with n = 1, 2, 3, 4, 8, 10, 12, 18, and 22. Water contact angles (θA/θR = ∼105°/∼94°) are independent of chain length, indicating that these surfaces project disordered methyl groups toward t...

Trialkylsilane Monolayers Covalently Attached to Silicon Surfaces: Wettability Studies Indicating that Molecular Topography Contributes to Contact Angle Hysteresis

It was in 1945 that researchers at the University of Chicago first reported that carbon tetrachloride could be added directly to olefinic double bonds (eq 1). This process was catalyzed by peroxides as radical initiators.1 This simple reaction is a classic example of anti-Markovnikov addition and has become known as the Kharasch addition reaction,2 in honor of its discoverer, M. S. Kharasch. In the late 1930s, Kharasch and independently Hey and Waters3 had presented a free-radical mechanism to explain this kind of addition reaction, and it is now generally accepted to occur in this manner.4 The use of the Kharasch addition is, however, often overlooked in synthetic organic chemistry although it has been employed in a number of specific syntheses. A few examples of these are shown in eqs 2-6.5-7 Both interand intramolecular Kharasch addition8 is possible.

/pdf/diaminoarylnickel-ii-pincer-complexes-mechanistic-1ua7ntyz8w.pdf

Diaminoarylnickel(II) “Pincer” Complexes: Mechanistic Considerations in the Kharasch Addition Reaction, Controlled Polymerization, and Dendrimeric Transition Metal Catalysts

Mechanism of dehydrogenation of secondary alcohols on chromia

Liquid chromatography on chemically bonded electron donors and acceptors

Aldehydes present in «clean» forest air (Niwot Ridge, CO, 3050-m altitude) were trapped on glass microcartridges containing porous glass particles impregnated with dansylhydrazine (DNSH) and analyzed on-line by HPLC with fluorescence detection. The detection limits of formaldehyde and acetaldehyde are 0.1 ppbv for 1-L air samples obtained at a sampling rate of 100 mL/min for 10 min. However, both field and laboratory studies show that, as for the conventional 2,4-dinitrophenylhydrazine method, ozone is a significant interference when its concentration exceeds 150 ppbv.

L. Nondek

Papers

Mechanism of dehydrogenation of secondary alcohols on chromia

Liquid chromatography on chemically bonded electron donors and acceptors

Measurement of sub-ppbv concentrations of aldehydes in a forest atmosphere using a new HPLC technique

Heterogeneous catalytic post-column reaction detectors for high-performance liquid chromatography application to n-methylcarbamates

Determination of surface hydroxyl groups on silanized silica gels for reversed-phase liquid chromatography