Equivalent methylene protons

The H NMR spectrum of propane contains two signals one for the six equiva lent methyl protons the other for the pair of equivalent methylene protons... 

The ll NMR spectrum exhibits a signal for the two equivalent methylene protons and one for the three equivalent methyl protons. Both these signals are sharp singlets. The protons of the methyl group and the methylene group are separated by more than three bonds and do not split each other s signals. 

In each case the 4H NMR spectra of l,3-dihydrobenzo[c]thiophene and its 2,2-dioxide exhibit a singlet for the four equivalent methylene protons. The spectrum of the unsymmetrical sulfoxide [shown in 81... 

The C-nmr spectrum of ion [100] obtained by the INDOR-technique showed equivalent methylene carbon absorptions at S -l- 138 1 (ref. CSa 7i,p = 180 5 Hz). The methine carbon appears at -1-85 but Ji, was not obtainable by the experimental technique used. It was concluded that the ion has two sets of equivalent methylene protons both of which are coupled to equivalent carbon atoms. It must either have high symmetry or be a set of rapidly equilibrating ions. 

This pyramidal structure of stannyl radicals is supported by the negative temperature dependence of a(119Sn) and by the fact that optically active organotin compounds with the asymmetry centred on the tin can react through the intermediate stannyl radical and show retention of optical activity. Again, the fact that the trineophyltin radical (PhMc2CCII2)3Sn shows non-equivalent methylene protons in the ESR spectrum below -20 °C is most readily explained by the fact that the radicals are non-planar at tin.53... 

Compound 3, todolactol D, [a]n +56.1° (c=0.46, acetone), was isolated as yellowish amorphous. The molecular formula was found to be CjjHjgOg (m/z 386.1726) from the HR-MS. The EI-MS had a M pea)c at m/z 386 and a base ion peak at m/z 340. The latter was caused by the elimination of a mole of water from the M". Interpretation of the H-NMR and C-NMR indicated that compound 3 had an acetal structure. Acetylation of 3 yielded diacetate 3a. In the H-NMR of 3a (Table 2.2), the triplet at 5 1.19 originated from the methyl protons in the ethoxy group. This signal was coupled with two multiplets (6 3.46 and 3.77) which can be assigned to the non-equivalent methylene protons in the ethoxy 1 group. The other peaks were very similar to... 

Figure 5 Designation of non-equivalent methylene protons in 3- Ribo (C2 -OH) and B-D-2 -Deoxyribo-Nucleoside derivatives when viewed along the 0(5 )-C(5 )-C(4 ) bond, H (5 I) is to the right and Hj[(5 II) the left when viewed along the C(l )-C(2 )-C(3 ) bond, Hj (2 I) is to the right and Hj (2 II) is to the left (Cramer et ai, 1975)...

As a generalization one can say that if a proton (or protons) is coupled with n other equivalent protons, then it will give rise to (n -h 1) peaks. Thus in an ethyl group, the methylene protons are coupled to three adjacent equivalent protons and hence their resonance is split into (3 -h 1) = 4 peaks. The methyl protons are coupled to the two equivalent methylene protons and their resonance is therefore split into (2 -h 1) = 3 peaks. This generalization is correct only when the coupled nuclei have a spin of A wider generalization would be... 

Dynamic n.m.r. methods have been used to determine the average lifetimes of the magnetically non-equivalent methylenic protons of the acetate groups in l,3-propylenediaminetetra-a( tate complexes of zinc and cadmium it is proposed that these lifetimes are a measure of the rates of partial dissociation of the complexes. The kinetics have been reported for the interaction between zinc and glycine. 

Figure 8.13 shows the spectrum of syndiotactic PBMA at 100 °C. Note that the multiplicities for the butyl side chain resonances do not seem consistent with the rules for scalar couplings. For example, the methyl resonances are an apparent quartet instead of the triplet that one expects from scalar coupling to two adjacent and equivalent methylene protons. Further scrutiny reveals that the resonances for... 

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