Effect of methyl groups

Shatenshtein et al.5 5 5- 591 have also measured rate coefficients for dedeuteration of thiophen derivatives by lithium or potassium l-butoxides in dimethyl sulphoxide or l-butyl alcohol (70 vol. %) in diglyme (Table 178). Interestingly, the 2 position is more reactive than the 3 position and this was reasonably attributed to the —I effect of the hetero sulphur atom. The methyl substituent lowers the reactivity of the 2 position from each position in accord with its +1 effect and consequently the effect was greatest from the 3 position. However, the deactivation from the 5 position was greater than from the 4 position, and this was incorrectly attributed to the +M effect of methyl group operating from the 5 position since... 

Bowden and Thomas report that the effect of methyl groups on the conductivity of trityl chloride in sulfur dioxide is in the order p>o>m> none.1 1 The trityl chloride-stannic chloride complex and a whole series of trityl bromides are strong electrolytes in sulfur dioxide.160-152 Benzhydryl chloride, ra-chlorobenzhydryl chloride, and -dimethylbenzhydryl chloride do not conduct in sulfur dioxide. Earlier reports to the contrary may have been due to the use of impure compounds.162 Dimesitylmethyl chloride has also been reported to conduct in sulfur dioxide.163... 

Here again the base-strengthening effect of methyl groups is clearly marked, as may be seen by comparing 2-methyl-butene-2 and 2,3-dimethylbutene-2 in Table 16. 

The theoretical calculations further permitted the high basicity to be explained and the effect of methyl groups on the basicity to be estimated, with some limitations. 

In calculations on proton addition complexes of azulene and methyl-azulenes by means of the HMO method, Heilbronner and Simonetta (1952) took the effect of methyl groups into aecount by adjustment of the a and j8 values, as had already been done by PuUmann and collaborators (1950) in calculating the spectra of the methylazulenes. These calculations correctly reproduce the effeet of a methyl group on the basicity of azulene. In contrast to the ease of naphthalene, the position of addition of the proton remains independent of the position of the methyl group ... 

In order to study the effect of methyl groups on the basicity of benzene more exactly, Ehrenson (1961, 1962) carried out calculations for the... 

The bathochromic effect of methyl groups is small (about 2 nm). An additional band in the region 305-345 nm (log e 3.48-3.76) was found in the spectra of the [b]-series and the benzo derivative. Only the thieno[b]tro-pylium salts exhibit a third band at 338-346 nm (log s 3.57-3.78). Dichloro-dimethyl compound 337b, compared with the tetramethyl derivative 337a, shows a bathochromic shift of about 10 nm (67JOC1610). 

The effect of methyl groups in the aromatic ring of 1-phenylethyl chloride is shown in Table 3. The small but significant rate increase of the o-CH3 group was reasonably ascribed to steric acceleration. 

Another clear example is the effect of methyl groups on B-subgroup metals. Table 11 compares stability data for mercury, thallium, and lead systems. There is now an effective reduction of (b)-class character due to the extra ligands CH3- This must be attributed to the lowered electron affinity of the metal orbitals if our discussion is correct. 

The short-range +1 effects of methyl groups are evident from the isolation of 46 and 38% yields of 3-oxides from 2-amino-4-methyl- and 2-methylamino-4-methylpyrimidines. In the former reaction, 7% of the 1-oxide was also observed (84CJC1176). 

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