Triplet 2-formyl phenylnitrene was generated by photolysis of 2-formyl phenylazide isolated in Ar, Kr, and Xe matrixes and characterized by IR, UV-vis, and EPR spectroscopies. Upon generation at 10 K, the triplet nitrene spontaneously rearranges in the dark to singlet 6-imino-2,4-cyclohexadien-1-ketene on the time scale of several hours. The intramolecular [1,4] H atom shift from the nitrene to the imino ketene occurs by tunneling, on the triplet manifold, followed by intersystem crossing. This case constitutes the first direct evidence of a tunneling reaction involving a nitrene.
Four cyanobutadiene
isomers of considerable interest to the organic
chemistry, molecular spectroscopy, and astrochemistry communities
were synthesized in good yields and isolated as pure compounds: (E)-1-cyano-1,3-butadiene (
E-1), (Z)-1-cyano-1,3-butadiene (
Z-1), 4-cyano-1,2-butadiene (2), and 2-cyano-1,3-butadiene
(3). A diastereoselective synthesis was developed to
generate (E)-1-cyano-1,3-butadiene (1) (10:1 E/Z) via tandem SN2 and E2′ reactions. The potential energy
surfaces of the E2′ reactions leading to (E)- and (Z)-1-cyano-1,3-butadiene (1) were analyzed by density functional theory calculations, and the
observed diastereoselectivity was rationalized in the context of the
Curtin–Hammett principle. The preparation of pure samples of
these reactive compounds enables measurement of their laboratory rotational
spectra, which are the critical data needed to search for these species
in space by radioastronomy.
Encouraging the persistence of underrepresented
populations in
STEM begins in gateway science courses like general chemistry. In
these courses, success often depends on students’ ability to
affirm their identity and sense of belonging in the science classroom.
General chemistry suffers from an unfortunate lack of diverse role
models; however, the instructor can use personal identity to help
remedy this problem. Actively affirming identity in the classroom
allows students from all backgrounds to feel like they belong in science.
Additionally, by sharing information about oneself, the instructor
is in a unique position to share power in the classroom, empowering
students to develop their own voices as scientists.
Photolysis (λ > 472 nm) of 2-diazo-3-pentyne (11) affords triplet 1,3-dimethylpropynylidene (MeC3Me, (3)3), which was characterized spectroscopically in cryogenic matrices. The infrared, electronic absorption, and electron paramagnetic resonance spectra of MeC3Me ((3)3) are compared with those of the parent system (HC3H) to ascertain the effect of alkyl substituents on delocalized carbon chains of this type. Quantum chemical calculations (CCSD(T)/ANO1) predict an unsymmetrical equilibrium structure for triplet MeC3Me ((3)3), but they also reveal a very shallow potential energy surface. The experimental IR spectrum of triplet MeC3Me ((3)3) is best interpreted in terms of a quasilinear, axially symmetric structure. EPR spectra yield zero-field splitting parameters that are typical for triplet carbenes with axial symmetry (|D/hc| = 0.63 cm(-1), |E/hc| = ∼ 0 cm(-1)), while theoretical analysis suggests that the methyl substituents confer significant spin polarization to the carbon chain. Upon irradiation into the near-UV electronic absorption (λmax 350 nm), MeC3Me ((3)3) undergoes 1,2-hydrogen migration to yield pent-1-en-3-yne (4), a photochemical reaction that is typical of carbenes bearing a methyl substituent. This facile process apparently precludes photoisomerization to other interesting C5H6 isomers, in contrast to the rich photochemistry of the parent C3H2 system.
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