Ultrafast X-ray Diffraction of Transient Molecular Structures in Solution.
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| Title: | Ultrafast X-ray Diffraction of Transient Molecular Structures in Solution. |
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| Authors: | Ihee, H., Lorenc, M., Kim, T.K., Kong, Q.Y., Cammarata, M., Lee, J.H., Bratos, S., Wulff, M. |
| Source: | Science (pre-March 2025). 8/19/2005, Vol. 309 Issue 5738, p1223-1227. 5p. 4 Graphs. |
| Subjects: | Molecular structure, Chemical structure, X-ray diffraction, Alkenes, Molecular dynamics, Strains & stresses (Mechanics) |
| Abstract: | We report direct structural evidence of the bridged radical (CH[sub 2]ICH[sub 2]•) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereochemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C[sub 2]H[sub 4]I[sub 2]) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with ∼0.01 angstrom spatial resolution and ∼100 picosecond time resolution: The loss of one iodine atom from C[sub 2]H[sub 4]I[sub 2] leads to the C-I-C triangular geometry of CH[sub 2]ICH[sub 2]•. This transient C[sub 2]H[sub 4]I then binds to an iodine atom to form a new species, the C[sub 2]H[sub 4]I-I isomer, which eventually decays into C[sub 2]H[sub 4] + I[sub 2]. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion. [ABSTRACT FROM AUTHOR] |
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| Database: | Psychology and Behavioral Sciences Collection |
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| Abstract: | We report direct structural evidence of the bridged radical (CH[sub 2]ICH[sub 2]•) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereochemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C[sub 2]H[sub 4]I[sub 2]) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with ∼0.01 angstrom spatial resolution and ∼100 picosecond time resolution: The loss of one iodine atom from C[sub 2]H[sub 4]I[sub 2] leads to the C-I-C triangular geometry of CH[sub 2]ICH[sub 2]•. This transient C[sub 2]H[sub 4]I then binds to an iodine atom to form a new species, the C[sub 2]H[sub 4]I-I isomer, which eventually decays into C[sub 2]H[sub 4] + I[sub 2]. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 00368075 |
| DOI: | 10.1126/science.1114782 |
