No-bond-resonance

P Fluonnation always strongly stabilizes carbamons both by induction and by negative (anionic) hyperconjugaQon, 7 The latter "no-bond resonance has been controversial, but its importance is now well established both theoretically [133, 134] and expenmentally [67] The X-ray crystal structures of salts 8 [fi5] and 9 [136] provide cogent evidence for negative hyperconjugation... 

Gleiter, R], and Gygax, R. No-Bond-Resonance Compounds, Structure, Bonding and Properties. 63,49-88 (1976). 

Note Had you been given the choice, CH3Br, you would not choose it due to a possible Baker-Nathan effect (no-bond resonance). In base, one result is protolysis ... 

The stabilization mechanism operating in aryl-substituted vinyl cations such as 9 can be qualitatively depicted by the Lewis resonance structures A-C (Scheme 4). There is hyperconjugation between the carbon atom C° which is described by the no-bond resonance structure B. In addition, -delocalization between the aryl ring and the C+ carbon atom is indicated by structures such as C. 

Gerischer, H., and Willig, F. Reaction of Excited Dye Molecules at Electrodes. 61, 31-84 (1976). Gleiter, R], and Gygax, R. No-Bond-Resonance Compounds, Structure, Bonding and Properties. 63,49-88 (1976). 

RA, unpublished data). By comparison, the large and unfavorable effect of benzoannelation on the stability of the benzenonium ion as reflected in its small negative pATR value (-2.3) compared with the larger negative values for the 1-naphthalenonium ion ( 8.0) and 9-phenanthrenonium ion (-11.6) is surprising (cf. Table 2, p. 44). The order is explained, however, if it reflects the relative magnitudes of the hyperconjugative stabilization of the ions, which in turn depends on the aromaticity of their no-bond resonance structures. 

The anomeric effect in terms of a stabilizing effect can be illustrated by the concept of "double-bond - no-bond resonance" (14, 15) shown by the resonance structures 4 and 2 or by the equivalent modern view (16, 17) that this electronic delocalization is due to the overlap of an electron pair orbital of an oxygen atom with the antibonding orbital of a C —OR sigma bond (12). 

These effects, which have also been called symbiosis, double bond-no bond resonance, clustering, or geminal or anomeric effect [54], can also be explained in terms of the HSAB principle X3C+ will be harder than H3C+ if X is hard. Accordingly, X3C+ will have a higher affinity for the hard X- than H3C+ will have [54]. 

Hine, J. Polar effects on rates and equilibria. VIII. Double bond-no bond resonance. /. Am. Chem. Soc. 1963, 85, 3239-3244. 

The compounds we shall discuss in this paper have aroused particular interest since 1958, when it was proven that they exemplify a peculiar type of electron delocalization, sometimes referred to as single bond-no bond resonance. This concept refers to a delocalization of a bonds rather similar to the well-known delocalization of -n bonds. 

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