Methyl groups, attraction

Aldehydes, Ketones, ndAcids. As with many aromatic compouads, the oxidatioa of methyl groups is an attractive synthetic route to both aldehydes and carboxyUc acids ia the quiaoliaes. The hydrolysis of dibromomethyl groups has also beea used for aldehydes and the hydrolysis of nitriles for carboxyhc acids. Detailed reviews of the synthesis of these compounds have appeared (4). 

The Henkel process provides a means to convert toluene to benzene and at the same time makes use of the methyl group. Neither of these two processes is economically attractive for use in the United States. 

Because of the electron-attracting properties of the ring nitrogen atoms, methyl groups undergo aldol-like condensations. For example, 3- and 4-methylpyridazine react with chloral to give 3- or 4-(2-hydroxy-3,3,3-trichloropropyl)pyridazine, and 4-methylpyridazine reacts with anisaldehyde to yield 4-(p-methoxystyryl)pyridazine. 

The acidic strength of various quinoxaline derivatives is also listed in Table II. -Methyl groups have an acid-weakening effect and quinoxalin-2-one (2-hydroxyquinoxaline) is, as expected, a weaker acid than quinoxaline-2-thione (2-mercaptoquinoxaline), The marked enhancement of the acidic strength of 5-hydroxyquinoxaline 1-methiodide compared to 5-hydroxyquinoxaline itself, is due to the electron-attracting property of the positively charged nitrogen, ... 

N-Benzoyl-Lalanine methyl ester is in turn about eight times more reactive than is its D enantiomer). The open-chain compounds may not bind to the enzyme in the same manner, however, as does the locked substrate. The conformation around the amido bond of the open-chain compounds, for example, can be transoid rather than cisoid (81). In addition, if equatorial 24 is considered to be the reactive conformer for both the Dand L enantiomers, and if the alanine methyl group is attracted to the hydrophobic aromatic binding subsite, then structures 34 and 38 would result. The L enantiomer of N-benzoyl-phenylalanine methyl ester 38 in this representation has approximately the same conformation as equatorial L-24. But attraction of the methyl of the D enantiomer to the location occupied by the methyl group of the L enantiomer causes the carbomethoxy group to move from the position it occupies in D-24. 

The importance of the three stereogenic centers became evident as two of the stereoisomers [(2S,3S,7S) and (2S,3R,7R)] were recognized early as sex pheromones and that other enantiomers and diastereoisomers were often found to be inhibitory to the attractive response. Recently, the sawfly pheromone field has undergone a major advance with the recognition that several sawfly species synthesize and utilize sex pheromones of different structural types than the 3,7-dimethylpentadecan-2-ols. Shorter and longer chain lengths (undecan-2-ols 2 and tridecan-2-ols 3) and an additional methyl group in position 9 or 11 (4 and 5) characterize these new pheromone discoveries (Fig. 1). With an ad-... 

Fig. 9. Effect of the chain length of hydrocarbons on the adsorption enthalpy and rates of desorption. (A) Hydrocarbon in interaction with zeolite framework. Methyl groups interact with the framework oxygen protons exhibit an additional attractive force. (B) Heat of adsorption as a function of carbon number for zeolites MFI and FAU in the acidic and non-acidic form. (C) Relative desorption rates of a C12, Ci6, and C20 alkane compared to octane at 348 K. Values calculated from the linear extrapolation of the heat of adsorption values shown in (B).

A positive AS° implies that the cis conformation is characterized by less degrees of freedom, a fact which can be attributed to a locking effect of the methyl group into a Cs conformation by virtue of attractive pi nonbonded interactions. 

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