Related Experiment Video
Updated: Jun 30, 2026

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
Published on: October 31, 2019
Temperature stability and photodimerization kinetics of beta-cinnamic acid and comparison to its alpha-polymorph as
Abstract:
Photoreactions of the alpha- and beta-polymorphs of trans-cinnamic acid were studied by (13)C CPMAS solid-state nuclear magnetic resonance spectroscopy, and the reactants and products were spectroscopically characterized in detail. Chemical shifts and chemical shift anisotropy tensors calculated using density functional theory (DFT) were found to be in good agreement with the experimental results and helped to identify the polymorphs and the individual assignments of reactant and photoproduct carbon atoms. The beta-polymorph is metastable. Its transformation into the alpha-cinnamic acid polymorph is monitored by temperature-dependent (13)C NMR spectroscopy. The transformation occurs at a very slow rate at room temperature but is highly accelerated at elevated temperatures. Analysis of the kinetics of the photoreaction shows that the beta-polymorph progresses at a slower rate compared to that of alpha-cinnamic acid. Based on chemical shift tensor values of reactants and products as obtained from 2D PASS spectra, the difference in reaction rates is suggested to be due to the higher amount of molecular reorientation of functional groups upon photoreaction and the larger distance between the reacting double bonds.
More Related Videos
09:33Determination of the Photoisomerization Quantum Yield of a Hydrazone Photoswitch
Published on: February 7, 2022
08:54Vibrational Spectra of a N719-Chromophore/Titania Interface from Empirical-Potential Molecular-Dynamics Simulation, Solvated by a Room Temperature Ionic Liquid
Published on: January 25, 2020
Related Concept Videos
¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
Stability of Substituted Cyclohexanes
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
UV–Vis Spectroscopy: Woodward–Fieser Rules
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.
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement