skip to main content

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Synthesis of methanediol [CH 2 (OH) 2 ]: The simplest geminal diol
Geminal diols—organic molecules carrying two hydroxyl groups at the same carbon atom—have been recognized as key reactive intermediates by the physical (organic) chemistry and atmospheric science communities as fundamental transients in the aerosol cycle and in the atmospheric ozonolysis reaction sequence. Anticipating short lifetimes and their tendency to fragment to water plus the aldehyde or ketone, free geminal diols represent one of the most elusive classes of organic reactive intermediates. Here, we afford an exceptional glance into the preparation of the previously elusive methanediol [CH 2 (OH) 2 ] transient—the simplest geminal diol—via energetic processing of low-temperature methanol–oxygen ices. Methanediol was identified in the gas phase upon sublimation via isomer-selective photoionization reflectron time-of-flight mass spectrometry combined with isotopic substitution studies. Electronic structure calculations reveal that methanediol is formed via excited state dynamics through insertion of electronically excited atomic oxygen into a carbon–hydrogen bond of the methyl group of methanol followed by stabilization in the icy matrix. The first preparation and detection of methanediol demonstrates its gas-phase stability as supported by a significant barrier hindering unimolecular decomposition to formaldehyde and water. These findings advance our perception of the fundamental chemistry and chemical bonding of geminal diols and signify their role as an efficient sink of aldehydes and ketones in atmospheric environments eventually coupling the atmospheric chemistry of geminal diols and Criegee intermediates.  more » « less
Award ID(s):
2103269 1800975
PAR ID:
10324715
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
119
Issue:
1
ISSN:
0027-8424
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ( , Proceedings of the National Academy of Sciences)
    null (Ed.)
    Since the postulation of carbenes by Buchner (1903) and Staudinger (1912) as electron-deficient transient species carrying a divalent carbon atom, carbenes have emerged as key reactive intermediates in organic synthesis and in molecular mass growth processes leading eventually to carbonaceous nanostructures in the interstellar medium and in combustion systems. Contemplating the short lifetimes of these transient molecules and their tendency for dimerization, free carbenes represent one of the foremost obscured classes of organic reactive intermediates. Here, we afford an exceptional glance into the fundamentally unknown gas-phase chemistry of preparing two prototype carbenes with distinct multiplicities—triplet pentadiynylidene (HCCCCCH) and singlet ethynylcyclopropenylidene (c-C 5 H 2 ) carbene—via the elementary reaction of the simplest organic radical—methylidyne (CH)—with diacetylene (HCCCCH) under single-collision conditions. Our combination of crossed molecular beam data with electronic structure calculations and quasi-classical trajectory simulations reveals fundamental reaction mechanisms and facilitates an intimate understanding of bond-breaking processes and isomerization processes of highly reactive hydrocarbon intermediates. The agreement between experimental chemical dynamics studies under single-collision conditions and the outcome of trajectory simulations discloses that molecular beam studies merged with dynamics simulations have advanced to such a level that polyatomic reactions with relevance to extreme astrochemical and combustion chemistry conditions can be elucidated at the molecular level and expanded to higher-order homolog carbenes such as butadiynylcyclopropenylidene and triplet heptatriynylidene, thus offering a versatile strategy to explore the exotic chemistry of novel higher-order carbenes in the gas phase. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al ( , Science)

    Solvent molecules influence the reactions of molecular hydrogen and oxygen on palladium nanoparticles. Organic solvents activate to form reactive surface intermediates that mediate oxygen reduction through pathways distinct from reactions in pure water. Kinetic measurements and ab initio quantum chemical calculations indicate that methanol and water cocatalyze oxygen reduction by facilitating proton-electron transfer reactions. Methanol generates hydroxymethyl intermediates on palladium surfaces that efficiently transfer protons and electrons to oxygen to form hydrogen peroxide and formaldehyde. Formaldehyde subsequently oxidizes hydrogen to regenerate hydroxymethyl. Water, on the other hand, heterolytically oxidizes hydrogen to produce hydronium ions and electrons that reduce oxygen. These findings suggest that reactions of solvent molecules at solid-liquid interfaces can generate redox mediators in situ and provide opportunities to substantially increase rates and selectivities for catalytic reactions.

     
    more » « less
  3. ; ; ; ( , 2023 AAAR Meeting)
    Abstract Number: 99 Working Group: Aerosol Chemistry Abstract Isoprene, the largest non-methane volatile organic species emitted into Earth’s atmosphere, reacts with hydroxyl radicals to initiate formation of secondary organic aerosol (SOA). Under low nitric oxide conditions, the major oxidative pathway proceeds through acid catalyzed reactive uptake of isoprene-epoxydiol isomers (IEPOX). We have recently established the structures of the semivolatile C5H10O3 uptake products (formerly designated “C5-alkene triols) of cis- and trans-β-IEPOX as 3-methylenebutane-1,2,4-triol and isomeric 3-methyltetrahydrofuran-2,4-diols. Importantly, both uptake products showed significant partitioning into the gas phase. Here, we report evidence that the uptake products along with their gas phase oxidation products constitute a hitherto unrecognized source of SOA. We show that partitioning into the gas phase results in further oxidation into low volatility products, including highly oxygenated C5-polyols, organosulfates, and dimers. In the chamber studies, gas phase products were characterized by online by iodide-Chemical Ionization Mass Spectrometry (I-CIMS) and particle phase products by offline analysis of filter extracts by HILIC/(-)ESI-HR-QTOFMS using authentic standards. The chamber studies show the potential for a substantial contribution to SOA from reactive uptake of the second generation gas phase oxidation products onto both acidified and non-acidified ammonium bisulfate seed aerosols. Identification of these previously unrecognized early-generation oxidation products will improve estimates of atmospheric carbon distribution and advance our understanding of the fate of isoprene oxidation products in the atmosphere. 
    more » « less
  4. ; ; ; ; ( , Photochemistry and Photobiology)
    ABSTRACT

    Criegee intermediates make up a class of molecules that are of significant atmospheric importance. Understanding their electronically excited states guides experimental detection and provides insight into whether solar photolysis plays a role in their removal from the troposphere. The latter is particularly important for large and functionalized Criegee intermediates. In this study, the excited state chemistry of two small Criegee intermediates, formaldehyde oxide (CH2OO) and acetaldehyde oxide (CH3CHOO), was modeled to compare their specific dynamics and mechanisms following excitation to the bright ππ* state and to assess the involvement of triplet states to the excited state decay process. Following excitation to the bright ππ* state, the photoexcited population exclusively evolves to form oxygen plus aldehyde products without the involvement of triplet states. This occurs despite the presence of a more thermodynamically stable triplet path and several singlet/triplet energy crossings at the Franck‐Condon geometry and contrasts with the photodynamics of related systems such as acetaldehyde and acetone. This work sets the foundations to study Criegee intermediates with greater molecular complexity, wherein a bathochromic shift in the electron absorption profiles may ensure greater removalviasolar photolysis.

     
    more » « less
  5. ( , 41st Meeting American Association for Aerosol Research)
    Isoprene, the largest non-methane volatile organic species emitted into Earth’s atmosphere, reacts with hydroxyl radicals to initiate formation of secondary organic aerosol (SOA). Under low nitric oxide conditions, the major oxidative pathway proceeds through acid catalyzed reactive uptake of isoprene-epoxydiol isomers (IEPOX). We have recently established the structures of the semivolatile C5H10O3 uptake products (formerly designated “C5-alkene triols) of cis- and trans-β-IEPOX as 3-methylenebutane-1,2,4-triol and isomeric 3-methyltetrahydrofuran-2,4-diols. Importantly, both uptake products showed significant partitioning into the gas phase. Here, we report evidence that the uptake products along with their gas phase oxidation products constitute a hitherto unrecognized source of SOA. We show that partitioning into the gas phase results in further oxidation into low volatility products, including highly oxygenated C5-polyols, organosulfates, and dimers. In the chamber studies, gas phase products were characterized by online by iodide-Chemical Ionization Mass Spectrometry (I-CIMS) and particle phase products by offline analysis of filter extracts by HILIC/(-)ESI-HR-QTOFMS using authentic standards. The chamber studies show the potential for a substantial contribution to SOA from reactive uptake of the second generation gas phase oxidation products onto both acidified and non-acidified ammonium bisulfate seed aerosols. Identification of these previously unrecognized early-generation oxidation products will improve estimates of atmospheric carbon distribution and advance our understanding of the fate of isoprene oxidation products in the atmosphere. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email