Zeugmatographic high resolution nuclear magnetic resonance spectroscopy. Images of chemical inhomogeneity within macroscopic objects

Abstract

CompoundIa Iv Ferrocene 6.88" 1,l'-Diacetylferrocene 7.05 7.41 4a 7.04 7.67 4b 7.22 7.73 4c 7.16 7.67 aIa and Iv are i0.05 eV. Calibration relative to HXe/@.3.5 (dt, J = 13, 2 Hz, 2 H); 2.9 (brd, J = 13 Hz, 2 H). Interesting, although the mass spectrum of 6d has a strong peak for the molecular ion (mle, 156 for C&"B79Br), the base peak occurs at m/e 76, which corresponds to a loss of HBr to the parent borabenzene ( C S H~B + ) .~ Treating 6d with excess tert-butyllithium followed by ferrous chloride produces bis( 1-tert-buty1borabenzene)iron (4c) in an overall yield of 28%: Mp, 144-145O; 'H N M R (CDC13), 7 8.85 (s, 18 H), 5.65 (d, J = 9 Hz, 4 H), 4.60 (m, 4 H), 4.40 (t, J = 5.5 Hz, 2 H); "B N M R (CDC13) 6 -24.6; mass spectral m/e, 322 (M', C 1 p H z s~~B 2~~F e ) ; uv (CzH50H) 214 (35000), 274 (2170), 312 (1320), 362 (660). 4b has also been produced analogously from 2d with methyllithium and presumably the synthesis could be extended to other 1-substituted analogs by varying the alkyllithium. Compounds 4a and 4b have recently been reported by H e r b e r i~h .~ Thus this synthesis provides a point of convergence for the two methods for producing borabenzenes.Like the previously reported complexes, data indicate that the 1 -substituted-borabenzene is a q6-ligand.1-3 s-Boron coordination to iron is suggested by the air-stability of 4 in contrast to their pyrophoric conjugate acids 6 and by the large upfield shift of 4 relative to 6 in the "B N M R spectra. Similarly the IH N M R chemical shift values show a considerably smaller range than those of q5-cyclohexadienyl iron complexes.'The S7Fe Mossbauer spectrum of 4a has been measured.The isomeric shift relative to NazFe(CN)5NO.2H20 is identical with that of ferrocene, 0.72 mm/sec, while the quadrupole splitting is 1.97 mm/sec, somewhat smaller than that of ferrocene (2.40 mm/sec). A similar reduction in the magnitude of the quadrupole splitting has been observed for ferrocenes with strongly electron withdrawing substituent^.^ This suggests 1 -phenylborabenzene withdraws somewhat more electron density from the iron than do the cyclopentadienyl rings of ferrocene, although the equality of the isomeric shift makes it improbable that there is any large electronic difference at iron. The ionization potentials of 4 have been measured by He(1) ionization, See Table I. The vertical ionization potentials are approximately 0.8 eV greater than ferrocene'O and indeed are similar to those of the electron withdrawing ferrocene 1 ,l'-diacetylferrocene.Friedel-Crafts acetylation of 4b with acetylchloride, aluminum chloride in methylene chloride at 0' gave a 20% yield of a monoacetyl product, 7b: mass spectral mle, 280 (M+, C~~H I~I~B~~~F~O ) ; ir (CDC13) 1662 cm-l; H N M R , 7 9.35 (s, 3 H), 9.13 (s, 3 H), 7.63 (s, 3 H), 5.90 (d, J = 8 Hz, 1 H), 5.50 (d, J = 9 Hz, 1 H), 5.34 (d, J = 9 Hz, 1 H), 4.8-4.3 (m, 5 H), 4.08 (d, J = 6 Hz, 1 H). Since only three a-protons are observed as higher field doublets, the acetyl group must occupy the 2-position. Bis( 1 -tert-butylborabenzene)iron...

Quantitative proton chemical‐shift imaging

“…The potential of chemical-shift imaging has long been appreciated (19,20) and several techniques have been developed, yet only a few reports of clinical applications have appeared. Several methods have been described which require time-varying gradients (21-23), but these cannot be implemented on most clinical imaging units.…”

“…For each phantom best-fit values of the parameters S0,J TI, and T I F were determined using Eqs. [13], [14], and [19].…”

Methodology of magnetic resonance imaging

“…13 (Lauterbur, 1972(Lauterbur, , 1973(Lauterbur, a, b, 1974a(Lauterbur, , b, 1977(Lauterbur, , 1979Edelstein et al 1980;Johnson et al 1983;Kumar et al 19750,6;Lauterbur et al 1975;Mansfield &Maudsley, 1976c, 19776;Mansfield, 1977;Hoult, 1979). In some procedures, two-dimensional (2-D) image reconstruction can be achieved by a 2-D Fourier transformation (Kumar et al I 975 fl > b).…”

“…The projection-reconstruction technique has first been introduced into NMR by Lauterbur (Lauterbur, 1972(Lauterbur, , 1973a1974a, b, 1977Lauterbur et al 1975). In X-ray tomography this type of imaging is used routinely (Brooks & Di Chiro, 1976;Shepp, 1980).…”

NMR chemical shift imaging in three dimensions.

“…A recent review (10) summarizes and compares many of these methods. With few exceptions (11,12), previous workers have used protons for NMR imaging because of signal/noise (S/N) considerations and because the proton signal from tissue comes predominantly from water and therefore is at a single resonant frequency. The latter condition is necessary because most imaging methods are unable to cope with a distribution ofresonant frequencies.…”