Study of base hydrogen bond in N,2,6-trichloro-p-benzoquinone imine with nuclear magnetic resonance and infrared spectroscopy. The assignment of syn and anti proton signals in the chloroimino group

Abstract

The nuclear magnetic resonance (n.m.r.) spectra of N,2,6-trichloro-p-benzoquinone imine (1) a n d the anisotropy effect of the chloroimino group are investigated. A comparison of the n.m.r. spectra of 1 with those of oximes with a similar structure shows that the extent of the anisotropy effect is the same for both the chloroimino and the hydroxyimino group. This is also confirmed by comparison of N-chlorocyclohexanimine with cyclohexanone oxime. A downfield shift of the C-H proton signal in solvents acting as a base is observed, which is interpreted in terms of a C-H . . -base hydrogen bond. The extent of the shift is different between syn and anti sides and this gives the definite assignment for these two types of proton signals. Namely, the high-field signal, the extent of the downfield shift being larger, is assigned to anti protons, and the low-field one to syn protons. This assignment is extended to oximes owing to the equality of the anisotropy effects of the hydroxyimino and the chloroimino group. The formation of the C-H . . . base hydrogen bond is confirmed by the infrared (i.r.) spectra, and the correlation between the extents of n.m.r. downfield shift and i.r. low wave number shift is discussed. Furthermore it is found that the behavior of benzene molecule as solvent is different between the chloroimino and the hydroxyimino compounds.Canadian Journal of Chemistry, 46, 2989Chemistry, 46, (1968 IntroductionThe assignment of syn and anti proton signals for oximes has been attempted by many workers. Phillips (1) assigned the anti proton to the highfield peak and syn to the low-field one, assuming that a large deshielding effect is caused by its proximity to the hydroxyl group. However, this notion is not confirmed on any definite experimental basis and cannot explain the phenomenon about oxime hydrochlorides (2, 3). Lustig (4) made an assignment of the syn and anti proton signals ofp-chlorobenzaldoxime, the structure of which had been determined by the X-ray diffraction (5). Karabatsos and his co-workers (6) assigned the resonance peaks of oximes and the related compounds by comparison of nuclear magnetic resonance (n.m.r.) spectra in aliphatic and aromatic solvents. However, this method is applicable only in the case where the nature of an interaction between the solute and solvent is known with certainty.In our previous papers, we have investigated the i1.m.r. anisotropy effect' of the hydroxyimino group and deduced the following conclusions: (a) The anisotropy effect arises mainly from the

Transformation of the Antibacterial Agent Sulfamethoxazole in Reactions with Chlorine: Kinetics, Mechanisms, and Pathways

“…The UV spectrum and observed half-life (∼48 h) for decay of a Product SMX2 isolate in aqueous solution matched those previously reported for NCBQ (29). In addition, the apparent reduction of Product SMX2 by sodium thiosulfate and its ability to oxidize potassium iodide were consistent with such a structure.The 1 H NMR spectrum of Product SMX2 (Supporting Information Figure S3) was also compatible with the NCBQ structure, where (i) signals corresponding to the methyl group and heterocyclic proton of SMX's isoxazole ring (as observed for pure SMX) were absent from the spectrum of Product SMX2 and (ii) instead of two aromatic proton signals (as observed for pure SMX), the spectrum of Product SMX2 exhibited four proton signals, presumably due to anisotropic effects created by the presence of an N-chlorimino group (32). Final confirmation of Product SMX2 as NCBQ was obtained from comparison of the former compound's UV spectrum and HPLC retention time to those observed for a standard of the latter.…”

Identity of a Purple Dye Formed by Peroxidic Oxidation of p-Aminophenol at Low pH

“…The NMR spectrum for p -benzoquinone imine (0.018 M in Et 2 O; see Table and Figure ) has not previously been reported in the literature and shows several unusual features that serve as a useful test of the computational models. Whereas protonated p -benzoquinone imine exhibits an AA′BB′ spectrum typical of a protonated para-substituted ring (Figure ), unprotonated p -benzoquinone imine in Et 2 O exhibits four substantially different chemical shifts because of the asymmetric deshielding effect of the lone pair . Whereas the deshielding of the imine proton (due to conjugation of the nitrogen electrons onto the aromatic ring) is well-known, the apparent double triplet and double quadruplet of the upfield resonances are unexpected and appear to be due to imine proton coupling, which is greater to the more distant ring protons.…”

“…Whereas protonated p-benzoquinone imine exhibits an AA 0 BB 0 spectrum typical of a protonated parasubstituted ring (Figure 11), unprotonated p-benzoquinone imine in Et 2 O exhibits four substantially different chemical shifts because of the asymmetric deshielding effect of the lone pair. 24 Whereas the deshielding of the imine proton (due to conjugation of the nitrogen electrons onto the aromatic ring) is well-known, the apparent double triplet and double quadruplet of the upfield resonances are unexpected and appear to be due to imine proton coupling, which is greater to the more distant ring protons. Molecular modeling results presented in Table 1 support this conclusion.…”

Nitrogen analogs of 1,4-benzoquinones. Activities against the ascitic sarcoma 180 of mice

“…Assignment of the NMR spectra of the quinone imines is based on the fact that the lone pair of electrons of the nitrogen atom causes a separation between syn and anti proton signals. 9 The NMR spectrum of lV-bromo-2,6dichloro-1,4-benzoquinone 4-imine in acetone-d6 shows a multiplet around 2.1, a singlet at 2.65, and two doublets around 7.5-8.0. The multiplet around 2.1 and singlet at 2.65 are both due to a small amount of undeuterated solvent used.…”