Fluorine substituent effects

Comparing the potentials across each row, we can test the idea of additivity of ortAo-substituent effects for 2-fluoro, 6-chloro, and then 2-fluoro-6-chloro substitution. The definition of a = 0 changes across each row to permit easy visual addition of the potentials in the physically appropriate manner to assess the degree of additivity of ort/io-chlorine and ort/io-fluorine substituent effects. For o-fluorotoluene and 2-fluoro-6-chlorotoluene, a = 0 denotes the (minimum-energy) pseudo-trans conformation for o-chlorotoluene, a=0 denotes the pseudo-cis conformation. The notion of additivity has considerable merit in all three electronic states. 

B.E. Smart, Fluorine substituent effects (on bioactivity), J. Fluorine Chem. 109(2001) 3-11. 

Table 8. Fluorine substituent effects on the 1 J(F, C) coupling in fluorinated derivatives of methane"...

There are several compilations and reviews of fluorocarbon physical properties [4, 5, 6 9,10, II I2, and only the boihng points, surface energies and activities, and solvent properties are discussed in this section to illustrate the charactenshc fluorine substituent effects... 

Fluorine-Substituent Effects on the Chemical, Physical and Pharmacological Properties of Biologically Active Compounds... 

Table 1.33 Calculated C—H bond dissociation energies (BDE, kcal/mol) for some fluo-rinated methanes an evaluation of a-fluorine substituent effect...

Sulfur amino derivatives provide no examples of planar configuration at N (Table 8). However, as a rule the On value in these molecules is far greater than the tetrahedral angle value of 109.5°. Solely in the case of FsSNF2, the angle is 107°. Such a low value, however, may be regarded as the result of the fluorine substituent effect, as observed in other fluoroamines. 

The problems that follow illustrate some of the ways that chemical shift calculations can assist in structure determination among compounds that contain benzene rings. The purpose of the first problem is to acquaint you with the online calculator at the URL referenced in Table 13.6. You will need the calculator for the substituent effect A of fluorine. With the exception of fluorine, substituent effects for the other atoms and groups are listed in the table. 

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