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Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyl(tropone)iron
Published on: August 12, 2019
Stereodefined Precursor-Based Preparation and Isomer-Resolved Spectroscopic Validation of trans-3-Penten-1-yne
Sung Man Park1, So Yeon Kim1, Wonchul Lee1
1Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Republic of Korea.
None:
The preparation and characterization of volatile cis/trans stereoisomers require controlled access to defined isomeric forms and independent validation of their molecular compositions under spectroscopic conditions. Here, we report the integrated synthetic-spectroscopic characterization of trans-3-penten-1-yne, a volatile C5H6 enyne stereoisomer. A stereochemistry-preserving preparation route using trans-crotonaldehyde, combined with Corey-Fuchs-type dibromoolefin formation, a trimethylsilyl-protected enyne intermediate, mild deprotection, and freeze distillation, enables the low-temperature isolation of a trans-enriched sample while minimizing evaporative loss. The isomeric composition is first determined via nuclear magnetic resonance (NMR) spectroscopy and then independently evaluated under jet-cooled gas-phase conditions using vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. The good consistency between the NMR- and VUV-MATI-derived trans/cis ratios indicates that the trans-enrichment of the isolated sample is retained during vaporization and supersonic expansion. The VUV-MATI spectrum yields the precise adiabatic ionization energy of the trans-isomer and enables the differentiation of its threshold features from those of the residual cis-component. Infrared-dip VUV-MATI spectroscopy, supported by anharmonic simulation, confirms the neutral-state vibrational fingerprint of trans-3-penten-1-yne, and Franck-Condon analysis reveals that the cationic vibronic structure is consistent with the ionization of the well-defined trans neutral precursor. This combined approach establishes VUV-MATI spectroscopy as a gas-phase analytical complement to NMR spectroscopy in analyzing volatile stereoisomeric hydrocarbons and provides a reliable framework for interpreting the congested ionization spectra of labile enyne systems.
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Stability of Conjugated Dienes
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
Structure of Conjugated Dienes
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...

