Electron-donating effects

Methacryhc acid and its ester derivatives are Ctfjy -unsaturated carbonyl compounds and exhibit the reactivity typical of this class of compounds, ie, Michael and Michael-type conjugate addition reactions and a variety of cycloaddition and related reactions. Although less reactive than the corresponding acrylates as the result of the electron-donating effect and the steric hindrance of the a-methyl group, methacrylates readily undergo a wide variety of reactions and are valuable intermediates in many synthetic procedures. 

AH ahphatic aldehydes and most ketones react to form cyanohydrins. The lower reactivity of ketones, relative to aldehydes, is attributed to a combination of electron-donating effects and increased steric hindrance of the second alkyl group in the ketones. The magnitude of the equiUbrium constants for the addition of hydrogen cyanide to a carbonyl group is a measure of the stabiUty of the cyanohydrin relative to the carbonyl compound plus hydrogen cyanide ... 

Substituent effects are often considerable, particularly when strongly electron-donating effects (to the aza-nitrogen) are present, when upheld shifts of up to 60 p.p.m. (2-NH2) may be observed. 

The reaction can proceed from both species 4 or 5 respectively. The strong electron-donating effect of one or even two 0 -substituents allows for the transfer of a hydride ion H onto another aldehyde molecule ... 

Generally, oxepins have a tendency to contract to a six-membered carbocycle when treated with acid. The driving force is the aromaticity of the phenol formed. However, when the less stable cyclohexa-2,5-diene-1,4-diol with an appropriate substitution pattern is treated with acid, the oxepin system is obtained. The treatment of cyclohexadienediols that are substituted with tert-butyl groups in the 2- and 6-positions and aryl at Cl and C4 with trifluoroacetic acid produces oxepins 1 with elimination of water.186 187 This reaction, however, is restricted to certain aryl substituents with at least some electron-donating effect. Generally, cyclohexa-2,4-dienone derivatives 2 are formed.187,188... 

Usually, C-mercury substituted phosphorus ylides are monomers and in order to stabilize these complexes the presence of a second substituent on the carbon is necessary to balance the electron-donating effect of the metal. However a dimeric complex 85 has been obtained by the reaction of mercuric halides HgX2... 

The difference in the reactivity of the two ends of the double bond in (13) is more subtle adduct (15) is formed so presumably the electron-donating effects of the methyl groups outweigh their bulk. 

It thus became clear that the improvement in properties of CVL as opposed to Malachite Green lactone was due to the electron-donating effect of the dimethylamino group in the 6-position of the phthalide ring. On this basis a far superior approach to that above was the incorporation of additional electron donors into the dialkylaminophenyl groups.39 Scheme 4 demonstrates the synthetic route to such compounds. 

The combination of mesomeric electron-donating effects of the methoxy groups and the high bond fixation of the system results in high reactivity of 1-methoxy- and 1,2-dimethoxybiphenylene [28, 63] with dichlorocarbene to produce a complex mixture of ring-expanded products (Scheme 7.9). 

Deuterium substitution rednces the electron affinity of organic snbstrates. The reduced electron affinity of deuterinm-snbstitnted analogs is due to the larger electron-donating effect of deuterium when compared to hydrogen. Its inductive constant is small bnt negative (-0.0011). The deuterium electron donor effect develops in organic ion-radicals also. 

It is clear that deuterium as a substituent has the electron-donating effect. In other words, it can decrease electron affinity of the whole molecule. Potentials of reversible one-electron reduction for naphthalene, anthracene, pyrene, perylene, and their perdeuteriated counterparts indicate that the counterparts exhibit slightly more negative potentials (Goodnow and Kaifer 1990, Morris and Smith 1991). For example, the measurable differences in the reduction potentials are equal to -13 mV for the pair of naphthalene-naphthalene-dj or -12 mV for the pair of anthracene-anthracene-djo. The possible experimental error does not exceed 2 mV (Morris and Smith 1991). In another example, in DMF with 0.1 M n-Bu4NPFg, the deuterated pyrenes were invariably found to be more difficult to reduce than pyrene itself. The largest difference observed, 12.4 mV, was between perdeuteriated pyrene and pyrene bearing no deuterium at all with standard deviations between 0.2 and 0.4 mV (Hammerich et al. 1996). 

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