A methyl groups

Transferases. Enzymes which transfer a group, possibly a methyl group or a glycosyl group, from one compound to another. The name of the group transferred is usually in-... 

BUTENE. As shown in Figure 38, a group attached to C-1 can migrate from position 1 to 3 (1,3 shift) to produce an isomer. If it is a methyl group, we recover a 1-butene. If it is a hydrogen atom, 2-butene is obtained. A third possible product is the cyclopropane derivative. The photochemical rearrangement of 1-butene was studied extensively both experimentally [88]... 

Example Hthanc is stable in the staggered gauche) con formation. The transition state for rotating a methyl group in ethane has the eclipsed con form at ion, A gcom etry optim i/ation start in g from an eclipsed eon formation yields th e tran sition state. 

Aromatic nitriles are converted into a methyl group with ammonium for-mate[109]. Aldehydes and ketones are reduced to alcohols[l 10],... 

When the 5-position is occupied by a methyl group, sulfonation takes place at C-4 (247). 

The monomethine cyanines with a methyl group on the chain (Table 2113) are prepared in a basic medium from a 2-alkyl-substituted thiazolium by condensation of an electrophilic reagent. 

In conclusion, in terms of electrophilic reactivity a methyl group in the 2-position is equally reactive in the two categories of heterocycles (selenazole and thiazole). Of the two positions ortho to nitrogen, only the 2-position is activated. The 5-position is sensitive to electrophilic reagents and resembles more closely the para position of a benzene ring. 

As in the case of the free bases, the substitution of a nuclear hydrogen atom by a methyl group induces a bathochromic shift that decreases in the order of the position substituted 4->5->2- Ferre et al. (187) have proposed a theoretical model based on the PPP (tt) method using the fractional core charge approximation that reproduces quite correctly this Order of decreasing perturbation. 

As early as 1889 Walker (320), using samples of thiazole, 2,4-dimethylthiazoie, pyridine, and 2,6-dimethylpyridine obtained from Hantzsch s laboratory, measured the electrical conductivity of their chlorhydrates and compared them with those of salts of other weak bases, especially quinoline and 2-methylquinoline. He observed the following order of decreasing proton affinity (basicity) quinaldine>2,6-dimethyl-pyridine>quinoline>pyridine>2,4-dimethylthiazole> thiazole, and concluded that the replacement of a nuclear H-atom by a methyl group enhanced the basicity of the aza-aromatic substrates. 

Thiazole-N-oxides are prepared by the action at low temperature (-10°C) of hydrogen peroxide in acetic acid (474). 4-MethyIthiazole and 2,4-dimethylthiazole afforded the corresponding N-oxides with yields of 27 and 58%, respectively (Scheme 88). Thiazole-N-oxides without a methyl group in the 2-position are so unstable that they have a tendency to form 2-hydroxythiazoles and are decomposed by oxidation, whereas a 2-methyl group would prevent such rearrangement (474). 

Mills and Smith (504) were the first, in 1922, to develop a systematic study of the reactivity of methyl groups fixed on nitrogen-containing heterocycles. While in alkylpyridines the 2- (or 6) and 4-positions are activated, only the 2-position in thiazole corresponds to an enhanced reactivity of the methyl groups in condensation with aldehydes 4- and 5-methylthiazoles bear inert methyl groups. Quatemization of the thiazole nitrogen enhances still further the reactivity of the methyl in the 2-position (cf. Chapter IX), but it does not increase the reactivity of a methyl group in the 4-position (504). The authors invoke the possibility for 2- (and 6) methylpyridine and 2-methylthiazole to pass, to some extent, into the reactive enamine form (245), while 4-methylthiazole could adopt such a structure only with the participation of an unusual formula such as 247 (Scheme 112). 

Substitution by a methyl group increases AG° and AH°, and this increase is attributed to polar effects. As can be seen from Table III-15, there is an increase in AG and AH° of roughly 1 kcal/mole for each methyl group. Similar effects have been observed with picolines and lutidines (151). There is only a slight difference for the isomeric compounds, the substituent effect being weakest for the 5-derivative. 

Benzoyl peroxide has been the most common source of phenyl radicals. But in reaction with thiazoles the benzoyloxy radical abstracts a hydrogen atom from the thiazole nucleus or from a methyl group in the case of methylthiazoles, giving by-products such as dithiazolyls or 2.2 -dithiazolylethane (183). The results obtained with benzoyl peroxide are summarized in Tables III-23, III-24. and III-25. 

On account of the high degree of stability of the thiazole ring a large variety of substituted derivatives yield thiazolecarboxylic acids upon oxidation. The oxidation of a methyl group or a substituted methyl group to a carboxyl group has been accomplished in a few instances. 

As just noted (Section 2 7) CH3 is called a methyl group In addition to having methyl groups at both ends n butane contains two CH2 or methylene groups Isobutane con tains three methyl groups bonded to a CH unit The CH unit is called a methme group... 

Both schemes count five carbon atoms m their longest continuous chain and bear a methyl group as a substituent at the second carbon An alternative numbering sequence that begins at the other end of the chain is incorrect... 

An alkyl group lacks one of the hydrogens of an alkane A methyl group (CH3 —) is an alkyl group derived from methane (CH4) Unbranched alkyl groups m which the point of attachment is at the end of the chain are named m lUPAC nomenclature by replac mg the ane endings of Table 2 2 by yl... 

Epichlorohydnn is the common name of an industrial chemical used as a component in epoxy cement The molecular formula of epichlorohydnn is C3H5CIO Epichlorohydnn has an epoxide functional group it does not have a methyl group Write a structural formula for epichloro hydrin... 

---