Secondary stereoelectronic effect

While the primary and secondary stereoelectronic effects have been invoked to rationalize products,21 there have been reports in series of polycyclic ketones in which regiochemistry of migration was not explained by these effects.22... 

In the extreme carbocation limit of (3.163) and (3.164), the stereoelectronic secondary-hyperconjugation effects therefore blend seamlessly into ordinary pi-type conjugation phenomena (Section 3.3), the two extremes always being linked by electronic continuity. 

The principle of microscopic reversibility predicts that the reverse process must follow the same path which is indeed stereoelectronically allowed the oxygen atom in T has two secondary electronic effects (n-o ) (one electron pair of the oxygen atom is anti peri planar to the C-N bond while the other is antiperiplanar to C —Y bond) and the nitrogen has one (the nitrogen electron pair is antiperiplanar to the C —Y bond). Thus, there are three secondary electronic effects (n-o ) in ] and by the ejection of Y to form 4, two of these (due to the two electron pairs antiperiplanar to the C—Y bond) have been transformed into primary electronic effects (n- ) in the product 4. The third secondary electronic effect remains a n-o interaction in the product. The ejection of Y can therefore take place with the help of the primary and one secondary electronic effects. 

In this publication the author describes the phenomenon that most times the thermodynamically less stable product (see 29) of the two possible rings (e.g. 5-exo and 6-endo) is formed. Today looking at the 5-exo cyclization it is known that, although the generated primary radical is less stable than a secondary one, stereoelectronic effects favor reaction to the kinetically controlled product. According to MO-calculations, for a successful cyclization, an angle of 70° of the incoming radical to the plane of the alkene-/alkyne-bond is necessary.11... 

In another study, tertiary secondary primary relative reactivity data (TSP selectivity) for the deprotonation reactions of alkylbenzene radical cations [ 153] showed that with both intra- and intermolecular TSP selectivity the order S > T > P is usually observed, suggesting that the combination of steric and stereoelectronic effects makes an /Pr group less reactive than Et, but still more reactive than Me. 

Denmark argued that the synclinal transition state 19 may be favored due to stabilization by stereoelectronic effects such as secondary orbital overlap or minimization of charge separation. The allylstannane HOMO and the aldehyde LUMO could participate in. secondary orbital overlap in transition state 19, with specific-interactions between the allylstannane a-carbon and the aldehyde oxygen [50, 55]. Alternatively, the preference for the synclinal transition state 19 can also be attributed to minimization of charge separation in the transition state, compared to the situation in the antiperiplanar transition state 20 [50, 56],... 

Lactone is reacted with trimethyloxonium tetrafluoroborate (Me30+BF4 ). The produce is next refluxed with sodium iodide in acetone until complete disappearance of the 5-lactone. By taking entropy effects, stereoelectronic effects and the relative ease of SN2 reaction on primary versus secondary v.v tertiary carbons into consideration, comment on the possible product(s) profile. 

Sinnott (1988) discusses ALPH and the generalized anomeric effect in the context of epiphenomena, that is, secondary symptoms, mere concomitants of something else not regarded as its cause or result. It is therefore important in our review to discuss the hypothesized stereoelectronic effect in phosphorus chemistry, but it is essential to describe the theoretical calculations, the interpretation of which has been used to formulate this hypothesis. 

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