Propane chemical shifts

The decreased shielding caused by electronegative substituents is primarily an inductive effect and like other inductive effects falls off rapidly as the number of bonds between the substituent and the proton increases Compare the chemical shifts of the pro tons m propane and 1 mtropropane... 

Protons are equivalent to one another and have the same chemical shift when they are m equivalent environments Often it is an easy matter to decide simply by mspec tion when protons are equivalent or not In more difficult cases mentally replacing a proton m a molecule by a test group can help We 11 illustrate the procedure for a sim pie case—the protons of propane To see if they have the same chemical shift replace one of the methyl protons at C 1 by chlorine then do the same thing for a proton at C 3 Both replacements give the same molecule 1 chloropropane Therefore the methyl protons at C 1 are equivalent to those at C 3... 

Fig. 1. 13C-NMR fast exchange-slow exchange transition for the conformational interconversion of cyclododecane in solution of propane-d, (left side) and in the solid by CP-MAS techniques (right side) at 75.47 MHz. The temperature decreases from top to bottom as indicated at the spectra. Chemical shifts are given at the signals and refer to TMS = 0 ppm. (Ref.7))...

Data related to the effect of P-halogen on the proton and carbon chemical shifts of CF2H or CF2 groups are scarce (Scheme 4.13), although there is a recent review of 13C spectra of chlorofluorocyclo-propanes.3... 

In the proton NMR, the presence of the electronegative oxygen tends to shift the position of the chemical shift downfield. This can be seen in Table 9-3 and in the proton NMR spectra of propanal (Figure 9-18). 

Figure 9-33 Schematic proton nmr spectra X and Y are nonmagnetic nuclei. For 2-propane derivatives, as at the top, the CH3 resonances are double because of the splitting produced by the single proton on C2. For the ethane derivatives, the right set of lines is always a triplet when observable because of the two protons of the X—CH2— group. We assume here that the chemical shifts of the CH Y3 protons are independent of the number of Y substituents.

The application of 59Co n.m.r. spectroscopy to the study of cobalt(m) complexes is beginning to expand.285,286 An n.m.r. study of the stereoisomers of propane-1,2-diamine (pn), en, acac, CF3acac, etc., showed that the chemical shifts do not appear to be related to the absolute configuration, but that larger linewidths are observed with lower symmetry complexes 286 The chemical shifts are larger for ob-lel than for mer-fac isomerism in Co(pn)3 +. 285... 

Protons that are beta to a nitrogen atom show a much smaller effect, usually absorbing in the range <51.1 to <5 1.8. These chemical shifts show a downfield movement of about 0.2 ppm resulting from the beta relationship. The NMR spectrum of propan-1-amine (Figure 19-8) shows these characteristic chemical shifts. 

The carbon NMR chemical shifts of diethylmethylamine, piperidine, propan-l-ol, and propanal follow. Determine which spectrum corresponds to each structure, and show which carbon atom(s) are responsible for each absorption. 

Lignin Models. l-(4-Hydroxy-3-methoxyphenyl)-2-(2-methoxyphcnoxy)propan-1,3-diol (VII). The 4-benzyloxy-a-keto precursor to VII was prepared as previously described (16), Treatment of this compound (70 mg, 0.17 mmole) in THF(2 mL)/H2O(0.1 mL) with 10% Pd/C under H2 (balloon), with stirring, for 3 hours gave a colorless oil (49 mg, 91%) which was shown to be VII by comparison (TLC and NMR) with authentic material. A 70 30 erythroAhreo ratio was indicated by 13C-NMR. The XH and 13C-chemical shifts (CDCI3) have been previously published (17), Compound VII enriched with 13C at Ca was prepared from labeled acetovanillone, which was prepared from guaiacol and acetic acid-l-13C by a procedure analogous with that described previously (16), The 7-13C enriched compound was made by simply utilizing 13C-formaldehyde in the synthesis. 

The a chemical shifts of the monosubstituted cyclopropanes correlate well with those of the corresponding methyl compound It is noted that Q in iodocyclo-propane absorbs at rather high field this is a manifestation of the not completely understood heavy atom effect ... 

In contrast to these cases, for the Rhir heterometallic cluster catalysts inside NaY zeolite the dramatic suppression of hydrogenolysis by increasing the Ir contents is interpreted in terms not of a simple ensemble size effect but of an electronic state associated with the electron deficiency, namely, d-hole orbital of the clusters, as discussed for the Xe NMR chemical shifts on the series Rhe- tlr /NaY (245). The remarkable difference in hydrogenolysis activity between Rh and Ir crystallites inside NaY arises from their electron-deficient sites, which favor C—C bond scission via the alkane carbonium intermediate (177). The C2/C3 selectivity is defined as the ratio of the rates of butane conversion to ethane (k ) to the rates of butane conversion to methane plus propane (k,) ... 

Figure 3-13 Calculation of the C chemical shifts of the indicated carbon in 2-methyl propane (isobutane) and in 2,2-dimelhylpropane (neopentane).

To utilize the substituent parameters given in Table 3-5, one adds the appropriate values to the chemical shift of the carbon in the analogous hydrocarbon, rounding off to the nearest ppm. As seen in Figure 3-15, the chemical shift of the 1 carbon of 1,3-dichloropropane may be calculated from the value (16) for the methyl carbon of propane and from the figures in Table 3-5. The chemical shift of the 3 carbon of cyclopentanol similarly may be calculated from the value (27) for cyclopentane. 

The principal values, 6n, 622, 633, of the chemical shift tensor were obtained for each form by CP/MAS NMR experiments. The orientation of the principal axes with respect to the molecular frame was investigated by P CP/single-crystal NMR for the complex with propan-2-ol. The principal axis 1 of both chemically equivalent phosphorus atoms is nearly parallel to the P-S bond and the principal axis 3 is very close to the P=S bond. The comparison of experimental P 6 parameters with theoretical data calculated by the DFT GIAO approach provided complementary information about the most sensitive NMR parameters, which best characterize the nature of the C-H -S contacts. 

Lios and Duddeck ° studied substituted l-(2-hydroxyphenyl)-3-naphthyl-l,3-propane-diones. The OH resonance falls in the range 93-102 ppm. The higher value was found in a derivative with a methoxy group meta to the OH group in question. The position of the tautomeric equilibrium could also influence the chemical shifts. 

If the two structures produced by mental replacement of two different hydrogens in a molecule by a test group are the same, the hydrogens are chemically equivalent. Thus, the six methyl protons of propane are all chemically equivalent to one another and have the same chemical shift. 

Figure 2. Chemical shift differences in the cyclopolymer and linear polymer of bis(p-vinylphenylfpropane. The standard was 1,3-bis(p-isopropylphenyl)propane.

Butyl alcohol, which was used as an internal standard for chemical shift measurements, has a resonance at 1.2333 ppm downfield from the. sodium salt of 3-(trimethylsilyl)-l-propane sulfonic acid. 

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