Substituents substitution, Table

Substituent Effects in Electrophilic Aromatic Substitution (Table 12 2, p 464)... 

Substituents affect the orientation of the reaction. The three possible disub-stituted products—ortho, meta, and para—are usually not formed in equal amounts. Instead, the nature of the substituent already present on the benzene ring determines the position of the second substitution. Table 16.1 lists... 

Evidence has been presented from F-nmr shielding effects in m- and p-substituted fluorobenzenes (10) that solvent interaction modifies the O/ values of a number of the substituents of Table V (specifically NMc2, NH2, NHCOMe, OMe, CH3SO, SF3, CF3SO, CF3, SO3ME, CN, CO2R, NO2 and MeCO). The indicated changes in Oj between hydrocarbon and weakly protonic solvents are... 

Scheme 9, path d). An increasing number of alkyl substituents at the benzylic carbon (toluene 28.6%, ethyl benzene 50.5%, isopropylbenzene 46.7% [191]) and electrolytes of lower nucleophilicity (TBAOAc, HOAc [192]) favor side chain substitution. Table 13 presents some selected examples of aromatic nuclear substitution with different nucleophiles X or HX (Eq. 19). 

Structural parameters of selected mononuclear complexes containing heteroatomic 7i-donor-substituted allenylidene ligands are summarized in Table 1. When these data are compared to those reported for related complexes bearing conventional alkyl or aryl substituents (see Table 1 of chapter All-Carbon-Substituted Allenylidene and Related Cumulenylidene Ligands ), a lengthening of the M=C bond... 

In benzenoid compounds, 2JCH of the substituted carbon becomes more positive when the electronegativity of the substituent decreases (Table 3.10) [128] ... 

The relative strength of a substituted benzoic acid and hence the value of cr depends on the nature and position of the substituent in the ring. For this reason, cr is called the substituent constant. Table 26-6 lists several substituent constants and these will be seen to correspond to the polar character of the respective substituents. Thus the more electron-attracting a substituent is, by either resonance or induction, the more acid-strengthening it is, and the more positive is its cr value (relative to H as 0.000). Conversely, the more strongly a substituent donates electrons by resonance or induction, the more... 

Another synthesis of aryl-substituted methylidynetricobalt nonacar-bonyls was developed by Dolby and Robinson (15) who found that chloro-methylidynetricobalt nonacarbonyl alkylate s aromatic compounds in a Friedel-Crafts-type reaction. High product yields were obtained when equimolar amounts of ClCCo3(CO)9 and aluminum chloride and an excess of the arene were stirred at 60°-70°C for 2 hours. When the arene was a solid, the reaction was carried out in dichloromethanc solution. Both ortho and para substitution was encountered, the size of the substituent (s) already present on the benzene ring appearing to determine the position of substitution (Table IV). Noteworthy is that milder temperature conditions affected the position of substitution thus, reaction of chlorobenzene with chloromethylidynetricobalt nonacarbonyl in dichloromethane at 42° gave... 

The question still remaining to be settled is that of the observed preferential attack at C-2 in the aminations of 3-substituted pyridines. This preferred orientation does not seem to depend on the electrical effect of the 3-substituent (see Table VII). Since an attempted kinetic study of the reaction has, until now, been thwarted by the insolubility of sodamide in the reaction medium,268 a somewhat related system was investigated,10 namely that involving the reaction between methoxide ion in methanol and 2-chloro-, 2-chloro-3-methyl-, and... 

The effects of substituting a phenyl group for —H or —Me at the silicon end of the Si=C bond has different effects on the rates of silene reactions depending on the substituents present at carbon. For example, the l,3,5-(l-sila)hexatriene derivatives 21a-c exhibit a significant decrease in reactivity toward methanol and acetone with increasing phenyl substitution (Table 11). This too is consistent with the stepwise mechanisms proposed for... 

The chemical information available through LFER is primarily the reaction constant p, but this value depends upon the substituent constants selected for the construction of the LFER. The u values available are ct, ct", ct" or and Ui, these quantities are listed, for many substituents, in Tables 7-1, 7-3, 7-4, 7-6, and 7-7. A reasonable approach is to plot log k against the substituent constant defined by a standard reaction that is expected to be most like the reaction under study. It is also reasonable to plot log k against several of the ct quantities, seeking the best correlation. [In choosing between two types of substituent constants, it is necessary to make use of substituents for which the two scales (say ct and rr, for example) are not themselves correlated, for otherwise both LFERs will be acceptable. ] The ct or o constants should be applicable to reactions that do not combine reaction sites and para substituents of the + and — type (push-pull systems capable of through resonance) for example, one would not expect ct" or o to provide good correlations for reactions of phenols or anilines substituted with nitro or cyano or for reactions of benzoic acids substituted with amino or methoxy. 

Recently, this methodology has been expanded towards the synthesis of 1-substituted vinylcyclopropanes. Thus, heating 0.5-1 equivalent of the appropriate cyclopropenone acetal in a dry aromatic solvent to 80-150°C for 30-48 h in the presence of an electron-deficient alkene afforded a cyclopropane. This was isolated after hydrolysis of the ketene acetal moiety. The [1-1-2] cycloaddition proceeded with a high degree of regio- (>92 8) and stereoselectivity (> 84 16), depending on the substituents (see table below). ... 

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