Related Experiment Video
Updated: Jan 30, 2026
Cell Aggregation Assays to Evaluate the Binding of the Drosophila Notch with Trans-Ligands and its Inhibition by Cis-Ligands
Published on: January 2, 2018
Propiolic Acid in Solid Nitrogen: NIR- and UV-Induced cis → trans Isomerization and Matrix-Site-Dependent trans → cis
Susy Lopes1, Timur Nikitin1, Rui Fausto1
1CQC, Department of Chemistry , University of Coimbra , 3004-535 Coimbra , Portugal.
Abstract:
Propiolic acid (HCCCOOH, PA) was studied experimentally by infrared spectroscopy in a nitrogen matrix and by ab initio calculations. The vibrational spectra of the cis and trans monomers (O═C-O-H dihedral equal to 0 and 180°, respectively) were measured and assigned. The trans-PA monomer was produced by selective vibrational excitation of the cis-PA monomer molecules trapped in different matrix sites. Broadband in situ UV irradiation (λ > 235 nm) of matrix-isolated PA yielded as product the higher-energy trans conformer, with no other photoproducts being detected. Two cis- cis dimers were also identified in the matrixes and characterized structurally and vibrationally. trans-PA was found to decay back to cis-PA in the dark, by tunneling, and the different lifetimes of the higher-energy PA conformer resulting from pumping different matrix sites and different experimental conditions (using a filter blocking the higher-energy IR radiation of the spectrometer source and without using such a filter) were discussed.
Related Concept Videos
02:37Disubstituted Cyclohexanes: cis-trans Isomerism
In cyclohexane, the substituents can occupy different positions generating distinct isomers....
02:02Cis-regulatory Sequences
02:02Cis-regulatory Sequences
02:34Structural Isomerism
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
02:52Stereoisomerism
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...