Matrix and Time-Resolved Infrared Spectroscopy of Chloro-p-nitrophenylcarbene and Related Species

Abstract

Chloro-p-nitrophenyldiazirine (2) was deposited in an argon matrix. Photolysis (350 nm) releases chloro-pnitrophenylcarbene (1) as a persistent species. The IR and UV-vis spectra of carbene 1 were obtained, and the IR spectrum was adequately simulated by density functional theory (DFT) calculations. The carbene has an intense IR vibration at 1206 cm -1 involving the carbene carbon and aromatic ring carbon. This band was observed by TRIR spectroscopy upon laser flash photolysis (355 nm) of 2 in heptane at ambient temperature. The presence of benzene did not influence the frequency of this vibration. The carbene lifetime as measured by TRIR spectroscopy (≈400 ns) is consistent with previous LFP studies utilizing UV-vis detection. Upon LFP of 2 in CCl 4 or CF 2 ClCFCl 2 the photogenerated carbene abstracts chlorine atom from solvent to form R,R-dichloro-p-nitrobenzyl radical with a TRIR band at 1316 cm -1 . Upon LFP of 2 in acetonitrile, acetone, methyl acetate, pyridine, and tetrahydrofuran ylide species were produced. The ylides had similar TRIR spectra with bands at 1584, 1504, and 1312 cm -1 .

Solvation and complexation of carbenes – a perspective

“…We also did not find spectroscopic evidence for CCl 2 πcomplexation with mesitylene (23) or durene (24), even though calculations predicted that these complexes should be as enthalpically favorable as the CCl 2 -anisole complexes. [27] Possibly, the sensitivity of our UV dectector is reduced in the 300-350 nm spectral region (where the most intense absorptions of the CCl 2 complexes of 23 and 24 are expected), because of strong background absorption by dichlorodiazirine (17).…”

“…Fig. (a)) . When PNPCC is generated in anisole, the absorptions of the carbene are replaced by new signals at 388 and 492 nm (cf.…”

Visualizing Carbene Equilibria

“…PNPCC also forms an O ‐ylide with THF . We were able to demonstrate the reversibility of O ‐ylide formation with diethyl ether (Et 2 O), di‐ n ‐propyl ether (Pr 2 O) and THF, and determine the associated equilibrium constants and thermodynamic parameters .…”

“…Donating substituents (Me, MeO) result in low values of K. Note that K for F 5 -PhCCl exceeds K for p-O 2 N-PhCCl (Table 2); pentafluorophenyl is a strong electron-withdrawing moiety (25). (14) PNPCC also forms an O-ylide with THF (29,30). We were able to demonstrate the reversibility of O-ylide formation with diethyl ether (Et 2 O), di-n-propyl ether (Pr 2 O) and THF, and determine the associated equilibrium constants and thermodynamic parameters (31).…”

Free radicals in superfluid liquid helium nanodroplets: A pyrolysis source for the production of propargyl radical

“…In the infrared region of the spectrum, direct absorption methods have been used to obtain rotationally resolved spectra of a number of such systems, in both gas cells [3,4] and free jet expansions [5][6][7][8][9][10][11][12][13][14][15][16]. The radicals of interest are typically produced by pyrolysis [5,6], microwave discharge [7][8][9][10][11][12], electric discharge [13][14][15][16] or photolysis [17][18][19][20][21][22][23][24]. For example, flash pyrolysis has been used to generate radicals in cold supersonic jets, as first demonstrated by Kohn et al [5].…”