Alkyl group size, effect

In comparison with the decomposition of taws-azoalkanes 20 a much larger group size effect has been found for the thermolysis rates of a few c/s-azoalkanes 24. Due to the repulsion of the free electron pairs on the two nitrogen atoms and due to steric interaction between the cis oriented alkyl groups cis azoalkanes 24 decom-... 

SURFACE AREAS. CO2 B-E-T surface areas of the unground and ground extracts were determined. The results are shown in Table III. O-methylation increases the surface area of the extract, but then the surface area of the extract decreases with increasing size of the added alkyl group. Ttit effect of... 

Figure 2. Effect of Alkyl Group Size on Coal Liquefaction Reactivity of Treated Wyodak Coal at I w Severity Reaction Conditions.

Effect of 0 -Alkyl Group Size upon Isomer Ratio in the Reaction of A7-Aukoxypyridinium Salts with Potassium Cyanide in Aqueous Ethanol at 20° for 30 Minutes ... 

Figure 17-5. Effect of alkyl group size on antiwear action of meth i...

The rate of reaction was slowed down by the presence of alcohols, the effect increasing with alcohol concentration and alkyl group size. The analysis of data allowed to discard an interpretation in terms of enzyme inhibition due to the binding of a single alcohol molecule to the protein. Data have been interpreted in terms of general... 

From Fig. 2 it can be seen that at low concentration alcohols play a destabilizing role on DNA helix conformation this effect increases with alcohol concentration and alkyl group size. At high concentration, on the contrary, the fraction of denatured DNA, in the case of methanol, reaches saturation whereas for the other alcohols it reaches a maximum and then decreases. The rate of decrease is higher for alcohols with longer alkyl chains. 

Strauss UP, Schlesinger MS (1978) Effects of alkyl group-size and counterirai type on behavior of copolymers of maleic-anhydride and alkyl vinyl ethtrs. 2. Fluorescence of dansylated copolymers. J Phys Chem 82(14) 1627-1632. doi 10.1021/jl00503a011... 

Experimental measurements of dipole moments give size but not direction We normally deduce the overall direction by examining the directions of individual bond dipoles With alkenes the basic question concerns the alkyl groups attached to C=C Does an alkyl group donate electrons to or withdraw electrons from a double bond d This question can be approached by comparing the effect of an alkyl group methyl for exam pie with other substituents... 

Whereas introducing a thiol moiety at C-7 markedly reduced the antibacterial activity relative to lincomycin (79), the 7(3)-7-deoxy-7-alkylthiolincomycins exhibited considerably enhanced antibacterial activity without apparent regard for the size of the alkyl group (80—82). A marked increase in gram-negative activity was shown when the 7(3)-substituent contained a 2- or 3-hydroxy or amino group, but this activity was insufficient to be effective in infected mice (83—85). 

Steric effects play a major role in determining the ortho para ratio in Friedel-Crafts alkylations. The amount of ortho substitution of toluene decreases as the size of the entering alkyl group increases along the series methyl, ethyl, /-propyl. No ortho product is found when the entering group is /-butyl. ... 

Further, for studying the role of pH and salt concentrations on bulk-electrostatic and non-bulk electrostatic contributions the same approach was made to experiments on the influence of the alcohols mentioned above on the oxygen affinity at various KC1 concentrations and pH-values 144,146). The results obtained indicate that at a low alcohol concentration the bulk-electrostatic contributions are dominant and that with increasing size of the alkyl group, alcohol and KC1 concentration, the nonbulk electrostatic, hydrophobic contributions increase. Recent results of kinetic measurements of 02 release show that cosolvents such as alcohols and formamide influence mainly the allosteric parameter L, i.e. -the equilibrium between T and R conformation and that the separation of the alcohol effects into bulk-electrostatic and hydrophobic (non-bulk electrostatic) contributions is justified. 

Brown and McDonald (1966) provided another type of kinetic evidence for these size relationships by determining secondary kinetic isotope effects in reactions of pyridine-4-pyridines with alkyl iodides. For example, the isotopic rate ratio in the reaction between 4-(methyl-d3)-pyridine and methyl iodide at 25-0 C in nitrobenzene solution was determined to be kjyfk = l-OOl, while that in the corresponding reaction with 2,6-(dimethyl-d6)-pyridine was 1-095. (Brown and McDonald (1966) estimate an uncertainty of 1% in the k jk values.) Furthermore, the isotopic rate ratio in the case of the 2-(methyl-d3)-compound increased from 1 030 to 1-073 as the alkyl group in the alkyl iodide was changed from methyl to isopropyl, i.e. the isotope effect increased with increasing steric requirements of the alkyl iodide. 

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