Boron, nuclear spin

Natural boron consists of two isotopes, I0B (19.6%) and UB (80.4%). Isotopically enriched boron compounds can be made and are useful in spectroscopic and reaction-mechanism studies. The boron nuclear spins, (10B, S= 3 nB, S = 3/2) are also highly useful in structural elucidation. For an example see page 244. 

Boron s electron deficiency does not permit conventional two-electron bonds. Boron can form multicenter bonds. Thus the boron hydrides have stmctures quite unlike hydrocarbons. The B nucleus, which has a spin of 3/2, which has been employed in boron nuclear magnetic resonance spectroscopy. 

Boron has 2 stable naturally occurring isotopes and the variability of their concentration (particularly the difference between borates from California (low in °B) and Turkey (high in °B) prevents the atomic weight of boron being quoted more precisely than 10.811(7) (p. 17). Each isotope has a nuclear spin (Table 6.1) and this has proved particularly valuable in nmr spectroscopy, especially for The great... 

This spurious contribution could be attributed to the presence of boron nuclei in the metallized wafer. Boron is present in nature with two stable isotopes (10B, nB), one having nuclear spin 3/2 and abundance of 80.3%, and the other nuclear spin 3 and abundance of 19.7%. The nuclei have non-zero electric quadrupole moments. 

Nuclear relaxation rates, iron-sulfur proteins, 47 267-268 Nuclear resonance boron hydrides and, 1 131-138 fluorescence, 6 438-445 Nuclear spin levels, 13 140-145 Magnetic properties of nuclei, 13 141-145 Nuclear testing... 

One interesting experiment combines several aspects of NMR spectroscopy, including multiple-dimensional NMR, the physics of spin systems, and the ability to study molecular organization, in the study of the spectra of a phospholipid (67). Another interesting experiment uses the difference in nuclear spin splittings observed for two different isotopes of boron to determine its isotopic ratio (68). Finally, one experiment combines 2D-NMR with computational chemistry in order to obtain complete assignment of terpene spectra (69). 

P couples to any other nucleus with a nuclear spin /> 0. Apart from H and (the latter is only observable in carbon NMR spectra), P nuclei couple to themselves (P—P coupling), fluorine ( F), boron ( B and "B), and a variety of metals, especially transition metals. 

For atoms like hydrogen and lithium case A is valid, beryllium, boron, carbon and nitrogen are clearly of case B and in these cases the nuclear spin-electron spin interaction should be positive. 

Although boron atoms have a nonzero nuclear spin, boron NMR is more complicated than proton NMR or C NMR. Why ... 

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