Electron-withdrawing -CN groups

A Dieckmann reaction of 7 and enol etherification provided trans-octalone 6 in 90% yield. An additional 10% of the transposed /3-ethoxy -enone 24 was also isolated. Compound 24 could easily be removed chromatographically (the first chromatography of the synthesis) and could be isomerized back to the 9 1 mixture in favor of 6 by resubjection to the etherification conditions. Compound 7 had three different CC Et groups, yet only the one adjacent to the CN group was attacked by the nascent ketone enolate. This selectivity, attributed to the effect of the powerfully electron-withdrawing CN group, was expected, as it was observed previously in the preparation of 3c.3 The selectivity of the enol ether formation was also expected from previous work. 

In contrast, the complex [Ni(mnt)2]2 was initially reported to be unreactive toward Mel (61) and it was speculated that the sulfur atoms are not sufficiently nucleophilic due to presence of the strongly electron-withdrawing CN group. Later investigations by Vlcek (65) reveal that the alkylation reaction does occur upon treatment with Mel, but the adduct decomposes rapidly in solution. The net reaction is described by Eq. 7. 

When such deprotonation is precluded, as in 94, R =Ph, R2=CN, nucleophilic addition of added methanol to the radical cation activated by the electron withdrawing CN group occurs to give 98 as the main product isolated in 43 % yield. Controlled potential electrolysis of 94, R=H, R =Ph, R2=CN produces 99 in modest yield (34%). It is suggested that this product results via dimerization of the intermediary radical cation. 

Electrodes of two-dimensional sheet polymers of phthalocyanines prepared by in situ reaction of tetracyanobenzene with thin metal films were prepared and characterized in their photoelectrochemical characteristics. Anodic photocurrents were detected, characterizing these films as n-type semiconducting materials. It was also found that such films could be reduced at more positive potentials than unsubstituted phthalocyanines. This change when compared to films of divalent unsubstituted phthalocyanines is caused by unreacted CN groups that were found in the films " . Such films therefore can be looked at as substituted phthalocyanines with electron-withdrawing CN groups which explains their photoelectrochemical characteristics. 

This carbocation is unstable because it is located next to an electron-withdrawing CN group that bears a 6+ on its C atom. This carbocation is difficult to form, so CH2=CHCN is only slowly polymerized under cationic conditions. 

This 2° carbocation is more stable because it is not directly bonded to the electron-withdrawing CN group. As a result, it is more readily formed. Thus, cationic polymerization can occur more readily. 

To verify Eqs. (46) and (47), use was made of the Vi and Vr values for the pyrimidine ring (Table XXII), and the values of the ap and hp coefficients calculated for substituted phenyl groups (Section IV,A,1). The parameters of Eqs. (46) and (47) are listed in Table XXIII. Table XXIV lists, as examples, the values of substituent constants found by NMR and calculated with the aid of these equations for 2-, 4-, and 5-pyrimidinyl groups with electron-withdrawing (CN) and electron-releasing (OMe) substituents in various positions of a pyrimidine ring. The agreement between the calculated and the determined values is fairly satisfactory. 

The substrates 90-93 (Scheme 17) all have two double bonds in the same relative position to the incipient radical center. One of these double bonds is captodative (-CN, -NMePh), with the other bearing an electron-withdrawing (CN or C02Me) or -releasing (PhCH20, PhS) group, or a phenyl substituent. In each case, cyclization is seen to favor, in some cases exclusively, formation of the captodative radical [55]. 

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