Ethyl protonation

Figure 2.97 3IP NMR spectrum (ethyl protons decoupled) of IrH5(PEt2Ph)2. (Reprinted from J. Inorg. Nucl. Chem., 1973, 33, 2195. Copyright (1973) with kind permission from Elsevier Science Ltd, The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK.)...

H NMR data has been reported for the ethylzinc complex, Zn(TPP—NMe)Et, formed from the reaction of free-base N-methyl porphyrin H(TPP—NMe) with ZnEti. The ethyl proton chemical shifts are observed upheld, evidence that the ethyl group is coordinated to zinc near the center of the porphyrin. The complex is stable under N2 in the dark, but decomposed by a radical mechanism in visible light.The complex reacted with hindered phenols (HOAr) when irradiated with visible light to give ethane and the aryloxo complexes Zn(TPP—NMe)OAr. The reaction of Zn(TPP—NMe)Et, a secondary amine (HNEt2) and CO2 gave zinc carbamate complexes, for example Zn(TPP—NMclOiCNEti."" ... 

In addition to these low field resonances the chemical shift of the coordinated methyl group falls at —0.19 and the methyl portion of the coordinated ethyl group has a chemical shift of —0.61. By comparing these numbers with the chemical shifts of the ethyl protons in the analogous ethyl porphyrin derivative (129), in which the resonance positions are all above —5, it has been concluded that there is little or no ring current in the corrin ligand system. 

The value of the pKa in CTAB is much lower than that in SDS (Table 1). This is true for both the acid and ester forms of the complexes. Further, there is a significant difference in the pKa between the acids and esters of the heme complexes (see Table 1). It is interesting that this difference is largest in the neutral TX-lOO ( 1.0) as compared to that in SDS and in CTAB ( 0.6). There is also a trend in the variation in pKa with substitution at 2, 4 positions of the porphyrin i.e. ethyl proton > vinyl (Table 1). This trend is qualitatively the reverse of the trend in the strength of electron withdrawing power of the substituents. 

Perhaps the strongest evidence in favour of episulfonium ion involvement comes from the isolation of the 4-substituted 1-acetyltetrahydropyridines (137) and (138). Product (138) arises by addition of another molecule of 2-methylpropanethiol to (135). 4-Ethyl-pyridine 1-oxide on reaction with 2-methylpropanethiol, acetic anhydride and TEA yields another type of tetrahydropyridine (137). In this case TEA promotes elimination by abstraction of an ethyl proton, before 2-methylpropanethiol can attack position 6. Conversely, tetrahydropyridines are formed when R=Me, Pr or Pr1, as 2-methylpropanethiol (Scheme 78) is a better nucleophile (at C-6) than TEA is a base (at the 4-substituent). A different tetrahydropyridine (139) is obtained if the starting TV-oxide has a vacant 4-position (Scheme 79). Structural determination of compounds of this type has been greatly facilitated by the availability of 13C NMR (78JHC785). It should be remembered that while 3-substitution... 

Complex Temperature (K) Pyrrole-H Phenyl protons o-H m-H p-H CH3 Propyl protons a-CH2 P-CH2 Ethyl protons y-CHj a-CH2 P-CH3 Methyl protons 1 X... 

Note that in all the cases considered in Table 2 the ethyl protons of the initial Et3GeCOPh demonstrate positive polarization (A). Therefore, the analysis of these effects in accordance with the existing rules11 allows us to conclude that partially reversible photodecomposition of the ketone both in the presence and in the absence of the radical traps occurs from the triplet excited state with the formation of the triplet radical pair comprised of Et3Ge and COPh radicals. The analysis employed the following -factor and hyperfine interaction values of the radicals g(Et3Ge ) = 2.0089, g( COPh) = 2.0008 and Ah(CH2) < 0.5 mT (for Et3Ge )12. 

The ethyl protons are represented by the triplet at —1.2 ppm coupled to the deshielded quartet at —4.1 ppm. The other CH3 group is represented by the doublet at —1.8 ppm, coupled to one of four alkene CH protons. Rather than attempting to interpret the higher-order multiplets, we turn to the 2-D spectra. 

The n.m.r. spectrum (60 MHz., CDC13 solution, Me4Si external standard) shows singlets at 53.75 and 2.72 and a triplet (7 = 7 Hz.) at 53.62 assignable to allylic protons and a methyl singlet at 52.10 in the appropriate ratio of 1 1 1 3. The ethyl protons produce complex multiplets at higher fields. (In the checker s specimen, these multiplets gave a cumulative intensity of 6 rather than the expected 5.)... 

The definition given above for a spin system as a collection of sets insulated from one another can be formalized A spin system consists of sets of nuclei that spin couple with one another but do not spin couple with any nuclei outside the spin system hence insulated. For example, ethyl isopropyl ether consists of two spin systems the ethyl protons and the isopropyl protons, which are insulated from each other by the oxygen atom. It is not necessary for all nuclei within a spin system to be spin coupled with all the other nuclei in the spin system. 

Of particular importance is the spectrum obtained from the reaction of Cp2TiCl2 with EtMgCl in ether. Hyperfine structure from Ti and from two equivalent H atoms are observed (107), the latter being proved conclusively by replacement of the ethyl protons in EtMgCl by deuterium, whereby the 1 2 1 triplet was replaced by a 1 2 3 2 1 quintet. The paramagnetic species was originally thought to be... 

Fascinating is the observation that when the reaction is performed in the probe of an NMR spectrometer, the cyclopropyl protons of the starting material increase in intensity initially while the vinyl protons intensity decreased and even became an emission signal. The absorption signals decrease in intensity at about the same rate as the consumption of the starting material. All the ethyl protons of the product showed enhanced adsorption while all the aromatic protons gave emission signals (Scheme 11.64). 

These phenomena may be attributed to the formation of four sets of nonequivalent aromatic protons and two sets of nonequivalent tert-butyl and ethyl protons due to the contribution of the asymmetric metal cation complexation on the one side of octaethyl ester 4 (Figure 8). However, no intramolecular hopping between two binding positions could be observed as with biscalix[4]arenes [29, 30]. This result might be attributable to the conformational changes in the other side of the binding site in the process of metal complexation. Further experiments on these metal complexations are currently in progress in our laboratory. 

The internal chemical shift values, A5 = 5CH3-6CH2, of ethyl protons of Pb(C2Hs)4 In CCI4 and in hexamethyltriamidophosphate were reported to be +0.005 and -0.005 ppm, respectively [12]. 

In order to rationally connect the NMR spectral information to the solution conformation of the oUgomers, the chemical shifts of the main-chain methylene and terminal methine or ethyl protons were computationally estimated by density functional theory (DFT) [78] calculation for some optimized conformers of 1 of n=2 and 2 of n=2 and 4. The conformer structures optimized by the semiempirical PM5 method [51] are shown in Fig. 17 with their heats of formation (PM5) and theoretical chemical shifts obtained by the LORG method [79] using B88 [80]... 

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