Ab initio study of the photodissociation of nitrosoalkanes and nitrosamines

Cimiraglia, Renzo; Persico, Maurizio; Tomasi, Jacopo

doi:10.1021/ja00292a026

Cited by 21 publications

(16 citation statements)

References 3 publications

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“…Photodissociation on the S 1 PES was theoretically studied by ab initio calculations combined with classical trajectory calculations. [13][14][15] The results of these calculations are in good agreement with the observed rotational alignment of the NO fragment and the negative anisotropy of the recoil velocities. 9,11 It was concluded that nitrosamines suffer deformation from a planar geometry to a pyramidal structure at the amine nitrogen atom, followed by dissociation on a repulsive PES.…”

Section: Introductionsupporting

confidence: 80%

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The photodissociation dynamics of N-nitrosopyrrolidine from the first and second excited singlet states studied by velocity map imaging

Wenge

Kensy

Dick

2010

Phys. Chem. Chem. Phys.

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The photodissociation reaction of N-nitrosopyrrolidine isolated and cooled in a supersonic jet has been studied following excitation to the S(1) and S(2) electronic states. The nascent NO (X[combining tilde] (2)Pi((1/2),3/2), v, j) radicals were ionized by state-selective (1 + 1)-REMPI via the A(2)Sigma(+) state. The angularly resolved velocity distribution of these ions was measured with the velocity-map imaging (VMI) technique. Photodissociation from S(1) produces NO in the vibrational ground state and the pyrrolidine radical in the electronic ground state 1 (2)B. About 73% of the excess energy is converted into kinetic energy of the fragments. The velocity distribution shows a strong negative anisotropy (beta = -0.9) in accordance with the npi*-character of the S(0)--> S(1) transition. An upper limit for the N-NO dissociation energy of (14 640 +/- 340) cm(-1) is determined. We conclude that photodissociation from S(1) occurs very fast on a completely repulsive potential energy surface. Excitation into the S(2)pipi*-state leads to a bimodal velocity distribution. Two dissociation channels can be distinguished which show both positive anisotropy (beta = 1.3 and 1.6) but differ considerably in the total kinetic energy and the rotational energy of the NO fragment. We assign one channel to the direct dissociation on the S(2) potential energy surface, leading to pyrrolidine radicals in the excited electronic state 1 (2)A. The second channel leads to pyrrolidine in the electronic ground state 1 (2)B, presumably after crossing to the S(1) state via a conical intersection.

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Section: Introductionsupporting

confidence: 80%

“…Hence it is very unlikely that this vibrational progression is due to the NN or NO stretch vibration, as proposed previously. 9,13,16 We prefer an assignment to an internal vibration of the Py fragment.…”

Section: Photodissociation Following Excitation To the S 1 Statementioning

confidence: 99%

The photodissociation dynamics of N-nitrosopyrrolidine from the first and second excited singlet states studied by velocity map imaging

Wenge

Kensy

Dick

2010

Phys. Chem. Chem. Phys.

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“…19−21 For diarylnitrosamines, photodissociation of NO· occurs from the singlet excited state. 15,22,23 The triplet state of diarylnitrosamine has a low propensity to dissociate NO·. 15 Later we will show that photoexpulsion of NO· from 1 and 2 is minor pointing to the importance of a triplet reaction in our system.…”

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confidence: 81%

Mechanism of Photochemical O-Atom Exchange in Nitrosamines with Molecular Oxygen

et al. 2015

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The detection of an oxygen-atom photoexchange process of N-nitrosamines is reported. The photolysis of four nitrosamines (N-nitrosodiphenylamine 1, N-nitroso-N-methylaniline 2, N-butyl-N-(4-hydroxybutyl)nitrosamine 3, and N-nitrosodiethylamine 4) with ultraviolet light was examined in an (18)O2-enriched atmosphere in solution. HPLC/MS and HPLC-MS/MS data show that (18)O-labeled nitrosamines were generated for 1 and 2. In contrast, nitrosamines 3 and 4 do not exchange the (18)O label and instead decomposed to amines and/or imines under the conditions. For 1 and 2, the (18)O atom was found not to be introduced by moisture or by singlet oxygen [(18)((1)O2 (1)Δg)] produced thermally by (18)O-(18)O labeled endoperoxide of N,N'-di(2,3-hydroxypropyl)-1,4-naphthalene dipropanamide (DHPN(18)O2) or by visible-light sensitization. A density functional theory study of the structures and energetics of peroxy intermediates arising from reaction of nitrosamines with O2 is also presented. A reversible head-to-tail dimerization of the O-nitrooxide to the 1,2,3,5,6,7-hexaoxadiazocane (30 kcal/mol barrier) with extrusion of O═(18)O accounts for exchange of the oxygen atom label. The unimolecular cyclization of O-nitrooxide to 1,2,3,4-trioxazetidine (46 kcal/mol barrier) followed by a retro [2 + 2] reaction is an alternative, but higher energy process. Both pathways would require the photoexcitation of the nitrooxide.

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“…The occurrence of this transition state is in agreement with previous studies which predicted a twisting of the N-N-O bonds leading to a barrierless path for dissociation on S 1 both in nitrosamine and N-nitrosodimethylamine. 18,19 Therefore, the first excited singlet surface exhibits a dissociative character with an only possible channel, the homolytic dissociation ͑5͒,…”

Section: -6mentioning

confidence: 99%

“…Photochemistry of nitrosamine and N-nitrosodimethylamine has been also studied theoretically; most of the work has been focused on N-N photodissociation after excitation at the lowest energy wavelength. Cimaraglia et al, 18 by means of the SCF-CI approach, estimated that the ground state dissociation energy amounts to 47.7 kcal/ mol ͑2.07 eV͒. The calculated vertical transitions S 0 -T 1 and S 0 -S 1 were, respectively, 62.1 kcal/ mol ͑2.69 eV͒ and 81.1 kcal/ mol ͑3.52 eV͒.…”

Section: Introductionmentioning

confidence: 99%

A complete active space self-consistent field study of the photochemistry of nitrosamine

Peláez

Arenas

Otero

et al. 2006

The Journal of Chemical Physics

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Photodissociation mechanisms of nitrosamine (NH2NO) have been studied at the complete active space self-consistent field level of theory in conjunction with atomic-natural-orbital-type basis sets. In addition, the energies of all the critical points and the potential energy curves connecting them have been recomputed with the multiconfigurational second-order perturbation method. Ground state minimum of nitrosamine has a C1 nonplanar structure with the hydrogen atoms of the amino moiety out of the plane defined by the N-N-O bonds. Electronic transitions to the three lowest states are allowed by selection rules: (i) S0-->S3 (7.41 eV) has an oscillator strength of f=0.0006 and it is assigned as an (npO)0-->(piNO*)2 transition, (ii) S0-->S2 (5.86 eV) has an oscillator strength of f=0.14 and it is assigned as an npN-->piNO* transition, and (iii) S0-->S1 (2.98 eV) has an oscillator strength of f=0.002 and it is assigned as an npO-->piNO* transition. It is found that N-N bond cleavage is the most likely process in all the photochemical relevant states, namely, S1 (1 1A"), S2 (2 1A'), and T1 (1 3A"). While S1 and T1 yield exclusively homolytic dissociation: NH2NO-->NH2 (1 2B1)+NO(X 2Pi), on S2 the latter process constitutes the major path, but two additional minor channels are also available: adiabatic homolytic dissociation: NH2NO-->NH2 (1 2A1)+NO(X 2Pi), and adiabatic oxygen extrusion: NH2NO-->NH2N (1 3A1)+O(3P). The excited species NH2 (1 2A1) experiences a subsequent ultrafast decay to the ground state, the final products in all cases the fragments being in their lowest electronic state. We have not found a unimolecular mechanism connecting excited states with the ground state. In addition, homolytic dissociation in the ground state, tautomerizations to NHNOH and NHNHO, and intersystem crossings to T1 are considered. The most favorable process on this state is the isomerization to NHNOH.

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Ab initio study of the photodissociation of nitrosoalkanes and nitrosamines

Cited by 21 publications

References 3 publications

The photodissociation dynamics of N-nitrosopyrrolidine from the first and second excited singlet states studied by velocity map imaging

The photodissociation dynamics of N-nitrosopyrrolidine from the first and second excited singlet states studied by velocity map imaging

Mechanism of Photochemical O-Atom Exchange in Nitrosamines with Molecular Oxygen

A complete active space self-consistent field study of the photochemistry of nitrosamine

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