This work reports the first ground-based atmospheric measurements of 26 halocarbons in Singapore, an urban-industrial city-state in Southeast (SE) Asia. A total of 166 whole air canister samples collected during two intensive 7 Southeast Asian Studies (7SEAS) campaigns (August-October 2011 and 2012) were analyzed for C-C halocarbons using gas chromatography-electron capture/mass spectrometric detection. The halocarbon dataset was supplemented with measurements of selected non-methane hydrocarbons (NMHCs), C-C alkyl nitrates, sulfur gases and carbon monoxide to better understand sources and atmospheric processes. The median observed atmospheric mixing ratios of CFCs, halons, CCl and CHCCl were close to global tropospheric background levels, with enhancements in the 1-17% range. This provided the first measurement evidence from SE Asia of the effectiveness of Montreal Protocol and related national-scale regulations instituted in the 1990s to phase-out ozone depleting substances (ODS). First- and second-generation CFC replacements (HCFCs and HFCs) dominated the atmospheric halocarbon burden with HFC-134a, HCFC-22 and HCFC-141b exhibiting enhancements of 39-67%. By combining near-source measurements in Indonesia with receptor data in Singapore, regionally transported peat-forest burning smoke was found to impact levels of several NMHCs (ethane, ethyne, benzene, and propane) and short-lived halocarbons (CHI, CHCl, and CHBr) in a subset of the receptor samples. The strong signatures of these species near peat-forest fires were potentially affected by atmospheric dilution/mixing during transport and by mixing with substantial urban/regional backgrounds at the receptor. Quantitative source apportionment was carried out using positive matrix factorization (PMF), which identified industrial emissions related to refrigeration, foam blowing, and solvent use in chemical, pharmaceutical and electronics industries as the major source of halocarbons (34%) in Singapore. This was followed by marine and terrestrial biogenic activity (28%), residual levels of ODS from pre-Montreal Protocol operations (16%), seasonal incidences of peat-forest smoke (13%), and fumigation related to quarantine and pre-shipment (QPS) applications (7%).

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Atomically precise synthesis of topological molecular carbons such as Möbius carbon nanobelts (MCNBs) represents a big challenge in synthetic organic chemistry as it requires careful control of both twist and strain. So far, only one singly twisted MCNB has been reported and the MCNBs with more than two twists remain unknown. Herein, we report the facile synthesis of the first triply twisted MCNB by rational design and via a synthetic route involving Suzuki coupling-mediated macrocyclization, Bi(OTf)3-catalyzed cyclization of vinyl ethers, followed by oxidative dehydrogenation. The Möbius band-like structure was unambiguously confirmed by X-ray crystallographic analysis, which also revealed coexistence of (P,P,P)- and (M,M,M)- enantiomers. The racemic isomers were resolved by chiral HPLC and the isolated enantiomers exhibited a large absorption dissymmetry factor (|gabs| = 0.019) according to circular dichroism spectroscopy, which can be explained by the fully conjugated structure and the desirable orientation of the electric and magnetic transition moments.

Expanded helicenes are expected to show enhanced chiroptical properties as compared to the classical helicenes but the synthesis is very challenging. Herein, we report the facile synthesis of a series of expanded helicenes Hn (n=1-4) containing 11, 19, 27 and 35 cata-fused benzene rings through Suzuki coupling-based oligomerization followed by Bi(OTf)3-mediated regioselective cyclization of vinyl ethers. Their structures were determined by X-ray crystallographic analysis. Enantiopure H2, H3, and H4 can be isolated by chiral HPLC and they all exhibit strong chiroptical responses with high absorption dissymmetry factor (|gabs|) values (0.020 for H2, 0.021 for H3, and 0.021-0.024 for H4).