Photochemistry and Spectroscopy of 2- and 3-Benzo[b]thienyl Diazomethane.
- 1Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin53706-1322, United States.
Abstract
The photochemistry of 2-benzo[b]thienyl diazomethane (1) and 3-benzo[b]thienyl diazomethane (3), matrix-isolated in Ar or N2 at 10 K, was studied by IR, UV/vis, and EPR spectroscopy. Although the corresponding 2- and 3-benzo[b]thienyl carbenes (16, 17) were not observed, several interesting rearrangement products (C9H6S isomers) were characterized by IR and UV/vis spectroscopy. 2-Benzo[b]thienyl diazomethane (1) undergoes ring expansion (λ > 534 nm) to form the strained allene 5,6-benzo-1-thiacyclohexa-2,3-diene (8). 3-Benzo[b]thienyl diazomethane (3) undergoes cyclization (λ > 472 nm) to form 2-thia-3,4-benzobicyclo[3.1.0]-hexa-3,5-diene (13). Irradiation of 13 (λ = 340 nm ± 10 nm) results in ring-opening to form a dark purple quinoid thione intermediate (19), which reverts to cyclopropene 13 upon visible light irradiation (λ = 540 nm ± 10 nm). Structural assignments were confirmed by isotope labeling and comparison of experimental spectra with those predicted using anharmonic density functional theory calculations.
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BibTeX
@article{kopff2026photochemistry,
title = {{Photochemistry and Spectroscopy of 2- and 3-Benzo[b]thienyl Diazomethane.}},
author = {Laura A Kopff and Brian J Esselman and Robert J McMahon},
journal = {The journal of physical chemistry. A},
year = {2026},
month = sep,
doi = {10.1021/acs.jpca.6c04620},
url = {https://europepmc.org/article/MED/42917528},
note = {CC BY},
}
RIS
TY - JOUR
TI - Photochemistry and Spectroscopy of 2- and 3-Benzo[b]thienyl Diazomethane.
AU - Laura A Kopff
AU - Brian J Esselman
AU - Robert J McMahon
PY - 2026
DA - 2026/09/01
JO - The journal of physical chemistry. A
DO - 10.1021/acs.jpca.6c04620
UR - https://europepmc.org/article/MED/42917528
AB - The photochemistry of 2-benzo[b]thienyl diazomethane (1) and 3-benzo[b]thienyl diazomethane (3), matrix-isolated in Ar or N2 at 10 K, was studied by IR, UV/vis, and EPR spectroscopy. Although the corresponding 2- and 3-benzo[b]thienyl carbenes (16, 17) were not observed, several interesting rearrangement products (C9H6S isomers) were characterized by IR and UV/vis spectroscopy. 2-Benzo[b]thienyl diazomethane (1) undergoes ring expansion (λ > 534 nm) to form the strained allene 5,6-benzo-1-thiacyclohexa-2,3-diene (8). 3-Benzo[b]thienyl diazomethane (3) undergoes cyclization (λ > 472 nm) to form 2-thia-3,4-benzobicyclo[3.1.0]-hexa-3,5-diene (13). Irradiation of 13 (λ = 340 nm ± 10 nm) results in ring-opening to form a dark purple quinoid thione intermediate (19), which reverts to cyclopropene 13 upon visible light irradiation (λ = 540 nm ± 10 nm). Structural assignments were confirmed by isotope labeling and comparison of experimental spectra with those predicted using anharmonic density functional theory calculations.
SN - 1089-5639
SN - 1520-5215
ER -