ON THE REGIOSELECTIVITY OF THE NUCLEOPHILIC AROMATIC PHOTOSUBSTITUTION. THE PHOTOREACTION OF 4-NITROVERATROLE WITH n-HEXYLAMINE.
4-Nitroveratrole is photosubstituted with n-hexylamine giving rise to two isomeric anilines, N-hexyl-2-methoxy-5-nitroaniline and N-hexyl-2-methoxy-4-nitroaniline.Mechanistic evidence indicates that the first is produced in an SN2Ar* reaction through singlet and triplet excited states, whereas the second arises from a radical ion pair via electron transfer from the amine to a triplet excited state.
ON THE REGIOSELECTIVITY OF THE NUCLEOPHILIC AROMATIC PHOTOSUBSTITUTIONS OF 4-NITROVERATROLE. A THREEFOLD MECHANISTIC PATHWAY.
4-Nitroveratrole (NVT) is photosubstituted with primary amines, piperidine and hydroxide ion.Primary amines and hydroxide ion cause replacement of the methoxy group in meta position with respect to the nitro group whereas piperidine photosubstitutes the methoxy group in para to the nitro group.Photoreactions with piperidine and hydroxide ion involve attack of the amine upon a triplet excited state of NVT.Mechanistic evidences indicate that the reaction with hydroxide ion is probably a SN23Ar* process whereas the reaction with piperidine involves a radical ion pair formed via electron transfer from the amine to a triplet excited state.Photoreactions with primary amines involve attack of the amine upon a singlet excited state of NVT (SN21 Ar* process).These results are discussed and justified in the context of nucleophile ionization potential considerations and ground state donor-acceptor complex formation abilities.
Photosubstitution-photoreduction mechanistic duality in the SET photoreactions of nitrophenyl ethers with amines. The role of the steps that follow the ET
Nitrophenyl ethers are photoreduced by primary amines in water through a mechanism initiated by single electron transfer that is in direct competition with the single electron transfer photosubstitution mechanism (S(N)Ar*-SET). Our results indicate that the preferred pathway does not depend on the electron donor or proton donor ability of the amine. The key factor that determines the progress of the photoreaction is the structure of the carbon skeleton of the amine, particularly the type of hydrogens on the carbon α to the amino group. A mechanistic rationale that includes hydrogen atom transfer as a key step is discussed.
Mir, Miquel,Marquet, Jordi,Massot, Oriol
p. 12603 - 12614
(2007/10/03)
The search for biochemical photoprobes. III. The photoreactions of 4-nitroveratrole and 2-fluoro-4-nitroanisole with bovine pancreatic ribonuclease A and with model nucleophiles
The photoreactions of 4-nitroveratrole (NVT) and 2-fluoro-4-nitroanisole (FNA) with bovine pancreatic ribonuclease A (RNAase A) and with model nucleophiles are described. From them it is concluded that 2-fluoro-4-nitrophenyl ethers constitute improved alternative biochemical photoprobes, specially for proteins where a number of good nucleophiles are present.
THE SEARCH FOR NEW BIOCHEMICAL PHOTOPROBES. II. THE NUCLEOPHILIC PHOTOSUBSTITUTION OF 2-FLUORO-4-NITROANISOLE.
The photosubstitutions of 2-fluoro-4-nitroanisole with several amines are studied.The preparative results, the thermal stability of the photochemical substrate, and the limiting quantum yield values obtained from photoreactions with several nucleophiles suggest the possible usefulness of 2-fluoro-4-nitrophenyl ethers as biochemical photoprobes.
Pleixats, R.,Figueredo, M.,Marquet, J.,Moreno-Manas, M.,Cantos, A.
p. 7817 - 7826
(2007/10/02)
THE PHOTOREACTIONS OF 2-FLUORO-4-NITROANISOLE WITH AMINES. THE SEARCH FOR NEW BIOCHEMICAL PHOTOPROBES
The photosubstitutions of 2-fluoro-4-nitroanisole with several amines are studied from the preparative and the preliminary mechanistic points of view.The possible usefulness of this structure as biochemical photoprobe is discussed.
Figueredo, M.,Marquet, J.,Moreno-Manas, M.,Pleixats, R.
p. 2427 - 2428
(2007/10/02)
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