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Observed chemical shift

In Table III a comparison is made between calculated and observed chemical shift values of a variety of allenes that were not included in the data set of Table I,... [Pg.255]

Stracture C, however, gives a much closer approximation to the observed chemical shift and thus may represent the preferred structure. The calculations also indicate a lengthened C(3)—C(4) (1.58A) and a contraction of the C(2)—C(3)—C(4) bond angle to 101.5°, both of which would be consistent with C—C hyperconjugatioiL... [Pg.322]

Recall that the observed chemical shift is 130.9. For the B3LYP geometry, all of the computations using the 6-31G(d) basis set—however augmented—are substantially less accurate than the one using the 6-311+G(2d,p) basis set. ... [Pg.105]

Eor ethylzinc chloride, CH3CH2ZnCl, and ethylzinc bromide, CH3CH2ZnBr, there is a linear relationship between the observed chemical shift and the ratio of ethylzinc halide to diethylzinc. Extrapolation of these lines to x=l (mol fraction of CH3CH2Z11X) gives predicted values for the average chemical shift that closely match those measured for these species. This indicates that for these two organozinc halides, the Schlenk equilibrium lies heavily on the side of the ethylzinc halide in toluene. However, in the case of ethylzinc iodide, CH3CH2ZnI, there is a... [Pg.94]

Observed chemical shift (number of Hz away from TMS) Spectrometer frequency in MHz... [Pg.446]

Having determined 60bserved> the mole fraction of acetic acid present is obtained from Eq. (5.5.3), which takes into account the stoichiometry of the reaction [Eq. (5.5.1)] and the fact that an equimolar feed was used. Equation (5.5.3) shows that the mole fraction of acetic acid present in the reaction mixture is obtained directly from the chemical shift values of the H resonance of the OH groups of the pure compounds and the observed chemical shift of the OH resonance of the reaction mixture ... [Pg.596]

As indicated in Chapter 2, the single fluorine substituent has an extremely broad range of observed chemical shifts, which include sulfonyl fluorides and acyl fluorides absorbing downfield in the region of +40 and +25 ppm, respectively, all the way up to fluoromethyltrimethylsilane, with its signal far upheld at -277 ppm. [Pg.48]

A misconception that we commonly encounter is that a spectrum can be a mixture of the salt and the free base. This is an excuse that is often used by chemists to explain an inconveniently messy looking spectrum Don t be tempted by this idea - proton transfer is fast on the NMR timescale (or at least, it is when you use a polar solvent ) and because of this, if you have a sample of a compound that contains only half a mole-equivalent of an acid, you will observe chemical shifts which reflect partial protonation and not two sets of signals for protonated and free-base forms. It doesn t happen - ever ... [Pg.97]

In practice the source is oscillated back and forth at a velocity that varies between 1 cm s 1. Samples with Fe in different chemical environments then absorb at different frequencies and the observed chemical shifts are correlated with electronic configurations in different environments. [Pg.293]

The observed chemical shifts of the 22 carbon atoms compare closely with those reported by Frank (38). The only significant difference observed was that of the dimethylamino carbons which were found at 48.5 ppm rather than at Frank s reported value of 41 ppm. This difference in chemical shifts can probably be ascribed to differing amounts of water present in the DMSO-dg solvents and hence in the pH of these respective solutions. [Pg.119]

Beyond routine analytical NMR data, a relatively large set of 13C NMR data is available for derivatives of the [l,2,4]triazolo[2,3- ][l,3,5]triazine 19 ring system <1995J(P1)801, 2002JHC327>. The experimentally observed chemical shifts are compiled in Table 1. [Pg.849]

B (right) Observed chemical shift (<50bs—<5l) as a function of total ligand concentration, LT. The points are values calculated from the exact simulation, and the curve is the best fit to Eq. (14), assuming no exchange contribution the value of Kj estimated from the fit is 6.2xl(T6 M. From Ref. [13] with permission. [Pg.317]

Duddeck s approach is largely empirical, he does assess the various transmission mechanisms believed to be responsible for the observed chemical shifts. [Pg.352]


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