Inductive effects trifluoromethyl group

Attack at the meta position leads to a more stable intermediate than attack at either the ortho or the para position and so meta substitution predominates Even the inter mediate corresponding to meta attack however is very unstable and is formed with dif ficulty The trifluoromethyl group is only one bond farther removed from the positive charge here than it is m the ortho and para intermediates and so still exerts a significant although somewhat diminished destabilizing inductive effect... 

Answer. Two factors contribute to the stabilization of carbanions by an adjacent trifluoromethyl group or other perfluorinated groups. Most obviously, the strong inductive effect of the highly electronegative fluorine atoms will tend to increase the... 

Dixon and Smart71 examined a series of fluorine-substituted phosphonium ylides. Fluorine stabilizes carbanions via an inductive effect, favouring pyramidal carbanions. Dixon and Smart argued that the first substitution of F on the ylidic carbon (H3P=CHF) causes the carbon to become very pyramidal (the sum of the angles at C is 338.5°), which reduces the potential overlap of the anionic orbital with any P orbitals. The leads to the long P—C distance of 1.723 A. The second F substitution (H3P=CF2) actually breaks the P—C bond and the system is best described as a weak interaction of phosphine with CF2. Trifluoromethyl groups act to stabilize the anions via hyperconjugation. This leads to a planar ylidic carbon in H3P=C(CF3)2. 

Lastly, as can be seen from the data at the bottom of Scheme 2.8, the inductive effect of a trifluoromethyl group affects chemical shifts of protons as distant as three carbons away. 

The inductive effects of the trifluoromethyl and trichloromethyl groups increase the electrophilic reactivities of the carboxonium ions when compared with those formed from acetophenone or acetaldehyde. 

The strong inductive effect of the three trifluoromethyl groups polarizes the bond between the carbon and hydrogen and makes the hydrogen very acidic (pKa = 7). In basic media, the compound is deprotonated, and the tris(trifluoromethyl)carbanion adds to the double bond of acrylonitrile in the sense of the Michael addition. It joins the P-position of acrylonitrile because of its lower electron density. The product is 4,4-bis(trifluoro-methyl)-5,5,5-trifluorovaleronitrile T [107],... 

The regiochemistry of Diels-Alder reactions with 3.3.3-trifluoropropene (1) shows that the inductive effect of a trifluoromethyl group increases the magnitude of the molecular orbital coefficient of the unsubstituted terminus, but the effect is not great enough to achieve high regioselectivity with dienes other than l-methoxy-3-(trimethylsiloxy)buta-l,3-diene (Danishefsky s diene, 4) compare the reaction of 1 with 2, 3, and 4. ... 

Similarly, electrophilic CHj radicals add faster to ethylene than to tetrafluo-rethylene, in which the inductive effects of the fluorine substituents make the double bond somewhat electron deficient. The reverse selectivity is shown by CH3 radicals, which are nucleophilic in character [24]. This parallels the observations in organic chemistry thatcarbonium ion formation is facilitated by replacement of hydrogens by alkyl groups and hindered by CF3 groups. There is a polarization of a electrons towards the trifluoromethyl group, whereas these electrons can be more effectively released by alkyl substituents. 

Other methylenecyclopropenes apparently owe their stability to inductive effects brought about by stron y electron-withdrawing groups. Thus l,2-bis-(trifluoromethyl) 4,4-bis-(p-tolyl)methylenecyclopropene (87) is a perfectly stable molecule with a dipole... 

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