Bonding resonance and

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

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

Chapter 1. Covalent Bonding, Resonance, and Bond Orbital Hybridization Papers SP 1 to SP 22 7... 

When attached to C=0, Ar s, like —Y (Problem 15.23), are electron-releasing by extended v bonding (resonance) and deactivate C=0. Two Ar s are more deactivating than one Ar. In ArCHjCOR only the electron-withdrawing inductive effect of Ar prevails consequently. ArCHj increases the reactivity of C=0. 

Double bond-no bond resonance (and equivalent molecular orbital descriptions) has been suggested to be involved (—R) (Figure 1.12). 

In order to account for the existence of hydrogen bonds we must consider the possible contributions of covalent bonding, resonance and electrostatic attraction and attempt to assess the importance of each. In short, we must ask how much each of the possible canonical structures (5-VI), (5-VII) and... 

Covalent Bonding, Resonance, AND Bond-Orbital Hybridization... 

As shown in Scheme 6.94, a set of resonance hybrids can be written in which delocalization of the C-H electrons (as is traditional for resonance structures the nuclei do not move) into the ring would cause the incoming electrophile to choose ortho- and para- over meta- substitution. This explanation has variously been called no-bond-resonance and the theory of hyperconjugation. Clearly, the same idea could also be used to account for the stabihty of tertiary carbocations over their secondary and primary analogues. One difficulty with the widespread acceptance of the idea of no-bond-resonance has been the observation that the nitration of other alkyl substituted benzenes such as (l,l-dimethylethyl)benzene (r-butylbenzene) (Figure 6.38), which is incapable of participating in the same way, is also enhanced relative to benzene (CeH ). Indeed, although (l,l-dimethylethyl)benzene (t-... 

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