Secondary organic aerosol (SOA) particles are formed from the oxidation of volatile organic compounds (VOC) in the atmosphere followed by deposition into the particle phase. The latter process is facilitated by low volatility oxidation products, which are especially capable of condensing onto pre-existing particles as well as participating in new particle formation. Highly oxygenated organic molecules (HOM) are formed in the atmosphere through autoxidation of VOCs. A significant portion of HOM are low volatility, constituting a large contribution to SOA formation. The oxidation of α-pinene by ozone is a canonical SOA system that has drawn significant attention. Autoxidation of α-pinene is unusually rapid and efficient, generating HOM on a sub-second timescale through a yet to be determined mechanistic pathway. To facilitate elucidation of autoxidation pathways via mass spectrometric monitoring of hydrogen abstractions and H/D exchanges, access to a range of previously unknown deuterated α-pinenes is required. Herein we report the synthesis of two new selectively deuterated α-pinene isotopologues: α-pinene-4,4-d2 from verbenone via sequential reductions with lithium aluminum deuteride and α-pinene-5-d1 in thirteen steps from Hagemann’s ester. In addition, we report progress toward the synthesis of α-pinene-1-d1 utilizing the photoisomerization of verbenone to chrysanthenone as a key step. Synthetic access to these three compounds will augment the current library of α-pinene isotopologues available to the atmospheric community.

Total synthesis of deuterated α-pinene isotopologues for elucidation of atmospheric oxidation pathways

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