Methyl and methylene groups

Zaera F and Floffmann FI 1991 Deteotion of ohemisorbed methyl and methylene groups surfaoe ohemistry of methyl iodide on Pt(111) J. Phys. Chem. 95 6297-303... 

As a polymer prototype consider an n-alkane molecule consisting of n methylenes and 2 methyl groups. How serious an error is made in M for different n s if the difference in molecular weight between methyl and methylene groups is ignored ... 

Figure 4 Comparison of average distances from the bilayer center along the bilayer normal for deuterated methyl and methylene groups distributed throughout the DPPC molecule computed from constant-pressure MD calculations and neutron diffraction measurements on gel and liquid crystalline phase DPPC bilayers.

Formulas for the analysis of surface sum-frequency generation spectrum by CH stretching modes of methyl and methylene groups. J. Chem. Phys., 96, 997-1004. 

Complex of strong bands due to the overlapping C-H stretching vibrations of the various methyl and methylene groups. 

In water-suppressed muscle spectra, contributions of lipids, methyl and methylene groups of creatine (Crs, Cr2), trimethylammonium-containing compounds (TMA), including signals from carnitine (Ct), choline (Cho), and taurine (Tau) are well observable as demonstrated in Fig. 15. Furthermore, small signals of histidine protons of carnosine (Cs) can be sometimes identified... 

Table 2.5 lists the additive values for representative fragments/and structural factors F. As an example, the infinite dilution distribution ratio of C2H5 C(0)0C2H5, ethyl propionate, between 1-octanol and water is obtained as follows. The carboxylate group contributes -1.49 to log P, each ethyl group contributes 0.89 -H 0.66 - 0.12 = 1.43 (for the methyl and methylene groups and... 

The influence of the solvent on chiroptical properties of synthetic polymers is dramatically illustrated in the case of poly (propylene oxide). Price and Osgan had already shown, in their first article, that this polymer presents optical activity of opposite sign when dissolved in CHCI3 or in benzene (78). The hypothesis of a conformational transition similar to the helix-coil transition of polypeptides was rejected because the optical activity varies linearly with the content of the two components in the mixture of solvents. Chiellini observed that the ORD curves in several solvents show a maximum around 235 nm, which should not be attributed to a Cotton effect and which was interpreted by a two-term Drude equation. He emphasized the influence of solvation on the position of the conformational equilibrium (383). In turn, Furakawa, as the result of an investigation in 35 different solvents, focused on the polarizability change of methyl and methylene groups in the polymer due to the formation of a contact complex with aromatic solvents (384). 

The vibrational modes of alkanes are common to many organic molecules. Although the positions of C—H stretching and bending frequencies of methyl and methylene groups remain nearly constant in hydro-... 

In contrast, an extremely low activity was observed for the gallium-modified silicalite-1. scrambling started first at 723 K, which clearly indicates that Bronsted acid sites are necessary to activate propane adsorbed on zeolites Ga/ HZSM-5 179,181. A low activity was also observed for C-2-propane adsorbed on zeolite HZSM-5 in the absence of gallium. On this catalyst, C scrambling was observed after heating at 573 K for 20 min, and the theoretical 2 1 ratio of the signal intensities of methyl and methylene groups was reached after 80 min at 573 K. 

In contrast, comparable rates were determined over platinum of low dispersion suggesting that isomerization occurs without alkene formation.161 The carbene-alkyl species (21) formed with the involvement of terminal carbon atoms is a probable surface intermediate in this selective mechanism. Highly dispersed platinum catalysts are active in nonselective isomerization in which the precursor species is the 22 dicarbene allowing ring closure between methyl and methylene groups. On iridium a pure selective mechanism is operative,162 which requires a dicarbyne surface species (23). 

When 2M3BN, deuterium labeled on the methyl group, is isomerized in the presence of Ni[P(0-p-tolyl)3]4 and ZnCl2 at 110°C, the deuterium label is found in both the methyl and methylene groups of the resulting 3PN (48). 

When DCN is substituted for HCN, propionitrile is formed in which deuterium is found in both methyl and methylene groups, indicating that the insertion of ethylene into the nickel-hydrogen bond is reversible and occurs rapidly compared to the irreversible coupling of Et and CN to give propionitrile. A singlet at z 7.97 is assigned to coordinated ethylene. 

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