The ultraviolet photodissociation of axial and equatorial conformers of 3-pyrroline

Abstract

Resolved sets of photoproducts arising from the photodissociation of axial and equatorial conformers of 3-pyrroline have been observed using H(Rydberg) atom photofragment translational spectroscopy following excitation in the wavelength range of 250-213 nm. 3-pyrroline (alternatively 2,5-dihydropyrrole) is a five membered partially saturated heterocycle in which the bonding around the N atom is pyramidal (sp(3) hybridized) and the N-H bond can lie either axial or equatorial to the ring. Careful analysis of total kinetic energy release data derived from H atom time-of-flight measurements reveals excitation of the 3-pyrrolinyl cofragment consistent with N-H bond fission in both the axial and equatorial conformers. This allows determination of the energy difference between the ground state conformers to be 340±50 cm(-1) and the N-H bond strength for axial and equatorial conformers as 31,610±50 and 31,270±50 cm(-1), respectively.

Electronically excited states and photochemical reaction mechanisms of β-glucose

“…3 and 6) show the typical behavior of an X-H detachment reaction (X being an oxygen, nitrogen or sulfur atom) as previously reported for the ps* and ns* states of phenol, 79-81 pyrrole [80][81][82][83] and several other aromatic and non-aromatic molecules. 80,81,[83][84][85] While the conical intersections for the hydrogendetachment reactions are located around 5.0 eV (cf. Fig.…”

“…Although the conical intersection for the C-O ring-opening reaction is about 1.0 eV lower in energy than the conical intersections for the hydrogen-detachment processes, we expect the latter to prevail due to the faster motion of the light hydrogen atom. This hypothesis, however, can only be proven by photofragmentation spectroscopy 81,84,85 or by computational studies of the non-adiabatic nuclear-wavepacket or mixed quantum-classical surface-hopping dynamics. 63,79,[86][87][88][89][90][91][92][93][94] Although we were unable to optimize the conical intersections for the C-C ring-opening reactions, we can confirm based While no photodissociation experiments have been performed on carbohydrates so far, numerous experiments have been performed on methanol.…”

Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging

“…The present results for iodocyclohexane should be contrasted with the results of our recent photofragmentation studies of the cyclic amines morpholine 40 and 3-pyrroline. 41 Both of the latter exist as axial and equatorial conformers, and both undergo prompt N-H bond fission following UV excitation. Kinetic energy measurements of the resulting H atoms allowed resolution of velocity subgroups originating from each conformer, but in neither case did we discern any conformer-specific differences in the pattern of energy disposal within the resulting radical partnerconsistent with the minimal impulse caused by loss of the light H atom.…”

Conformer-Resolved Quantum Dynamics Study of the Photodissociation of 3-Pyrroline

“…Only weak coupling between the X̃and A(3s/ πσ*) states is found to exist at this point. However, a large variation of the first-order interstate coupling constants λ α (1,2) (R) with the N−H bond length is found. Specifically, at the conical intersection between the X̃and A(3s/πσ*) states (located at R = 1.66 au, corresponding to an N−H bond length of 3.58 au), the states X̃and A(3s/πσ*) are found to be coupled strongly by the degrees of freedom Q 4 , Q 17 , and ϕ.…”