Bonding resonance

Can you provide a rationalization of this difference in terms of both valence bond-resonance and PMO considerations Explain. 

Aldiough diese structures have a positive charge on a more electronegative atom, diey benefit from an additional bond which satisfies file octet requirement of the tricoordinate carbon. These carbocations are well represented by file doubly bonded resonance structures. One indication of file participation of adjacent oxygen substituents is file existence of a barrier to rotation about the C—O bonds in this type of carbocation. 

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... 

Peptide bond resonance has several important consequences. First, it restricts free rotation around the peptide bond and leaves the peptide backbone with only two degrees of freedom per amino acid group rotation around... 

Bonds resonate between single/triple and double... 

The values in Table 2.4 show how resonance affects the strengths of bonds. For example, the strength of a carbon-carbon bond in benzene is intermediate between that of a single and that of a double bond. Resonance spreads multiple bond character over the bonds between atoms as a result, what were single bonds are strengthened and what were double bonds are weakened. The net effect overall is a stabilization of the molecule. 

Three years ago it was pointed out2 that observed values of interatomic distances provide useful information regarding the electronic structures of molecules and especially regarding resonance between two or more valence bond structures. On the basis of the available information it was concluded that resonance between two or more structures leads to interatomic distances nearly as small Us the smallest of those for the individual structures. For example, in benzene each carbon-carbon bond resonates about equally between a single bond and a double bond (as given by the two Kekul6 structures) the observed carbon-carbon distance, 1.39 A., is much closer to the carbon-carbon double bond distance, 1.38 A., than to the shrgle bond distance, 1.54 A. 

Through these four points we draw a smooth curve, as shown in Fig. 1, which we accept as representing the dependence of carbon-carbon interatomic distance on double-bond character for single bond-double bond resonance. We believe that by a suitable translation and a change of vertical scale (to give the correct end-points) the same function can fee used for bonds between other atoms, and probably also for double bond-triple bond resonance. This use of the curve will be illustrated below. 

Fig. 1.—The empirical function expressing the dependence of carbon-carbon interatomic distance on bond character for single bond-double bond resonance.

Dec., 1935 Single Bond-Double Bond Resonance and Interatomic Distances 2707... 

The Dependence of Bond Angles on Single Bond-Double Bond Resonance.—In a molecule such as phosgene or 1,1-dichloroethylene the value 125°16 for the angle Cl-C-0 (0) is predicted by the theory of the tetrahedral carbon atom in case that the C-Cl bonds have no double bond character. If the double bond resonates equally among all three positions, giving the Cl-C bond one-third double bond character, we expect from symmetry... 

The possibility that only some of the outer electrons enter into bond formation needs to be considered. There is a close relation between interatomic distance and bond type, and the values of the interatomic distances in the sequence6 K, A2, 4.62A Ca, Al,A3, 3.93-3.95A Sc, not yet investigated Ti, A3, 2.92-2.95A V, A2, 2.63A Cr, A2, 2.49A, as well as those in the similar sequences from Rb to Mo and Cs to W, indicate that the number of bonds resonating among the available positions increases from one to nearly six. 

J >, in which one bond resonates independently from one position... 

The metallic form of tin, white tin, consists largely of the bivalent atoms SnB, which have a metallic orbital. In white tin each atom has co-ordination number 6, and the bonds resonate among the alternative positions. It is the energy of this... 

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