NMR spectroscopic characterization of new 2,3‐dihydro‐1,3,4‐thiadiazole derivatives

The ¹H and ¹³C NMR resonances of twenty‐seven 2,2‐dimethyl‐5‐(2‐nitrophenyl‐5‐substituted)‐2,3‐dihydro‐1,3,4‐thiadiazoles, and twenty‐seven 3‐acyl‐5‐(2‐amino‐5‐substituted)‐2,2‐dimethyl‐2,3‐dihydro‐1,3,4‐thiadiazoles were assigned completely using the concerted application of one‐dimensional and two‐dimensional experiments (DEPT, HMQC and HMBC). NOESY experiments, X‐ray crystallography and conformational analysis confirm the preferred conformation of these compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

2,3‐Diethoxy‐9,10‐anthraquinone

Anthraquinone derivatives form an important class of dyes and are also known for their medicinal properties. Recently, 2,3‐disubstituted anthraquinones have been shown unexpectedly to jellify various organic solvents. No information on the packing mode of these derivatives was known. Here, the first X‐ray structure of a 2,3‐disubstituted anthraquinone is reported, namely 2,3‐diethoxy‐9,10‐anthraquinone, C₁₈H₁₆O₄. The merit of this study lies in the observation of significant differences between the packing in 9,10‐anthraquinone, which displays a herring‐bone arrangement, and that in the title 2,3‐diethoxy derivative, in which the molecules lie on parallel crystallographic morror planes separated by a distance of 3.4081 (1) Å, reminiscent of the graphite layer architecture.     

Pyrazine‐2,3‐dicarboxamide

In the crystal structure of the title di­amide, C₆H₆N₄O₂, linear tapes of carbox­amide N—H?O and pyrazine C—H?N hydrogen‐bond dimers are connected by N—H?O bonds to form a staircase‐like pattern.     

5‐Fluoro­indoline‐2,3‐dione

In the title compound (5‐fluoro­isatin), C₈H₄FNO₂, the N atom of one mol­ecule is linked to the amido‐O atom of an adjacent mol­ecule across a center of symmetry by a cyclic hydrogen bond [N?O = 2.888 (4) Å].     

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

2,3‐Dimethyl‐2,3‐dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour‐phase detection systems. In this study, the formation and detection of gas‐phase [M+H]⁺, [M+Li]⁺, [M+NH₄]⁺ and [M+Na]⁺ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]⁺ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]⁺ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision‐induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source‐formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]⁺ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.     

One‐step preparation of some 2‐isopropenyl‐2,3‐dihydronaphtho‐[2,3‐b]furan‐4,9‐diones

Some 2‐isopropenyl‐2,3‐dihydronaphtho[2,3‐b]furan‐4,9‐diones la‐f,b',f were prepared by one‐step cyclizations of 2‐hydroxy‐1,4‐naphthoquinones 2a‐f with 1,4‐dibromo‐2‐methyl‐2‐butene ( 3 ).     

Two new isatin derivatives: 1‐benzyl‐4,5,6‐trimethoxyindoline‐2,3‐dione and 1‐benzyl‐5‐fluoroindoline‐2,3‐dione

Isatin (1H‐indole‐2,3‐dione) derivatives represent synthetically useful substrates which can be used to prepare a broad range of heterocyclic compounds. In the title compounds, C₁₈H₁₇NO₅, (I), and C₁₅H₁₀FNO₂, (II), the isatin ring systems are planar and form a dihedral angle of 73.04 (7)° in (I) and 76.82 (11)° in (II) with the benzyl groups. The bicyclic scaffolds in both compounds are almost superimposable, with an r.m.s. deviation of 0.061 Å. The crystal structures of both derivatives are stabilized by C—H...O interactions. These contacts generate an R¹₂(7) ring motif in (I) and a C(7) chain motif in (II).