Homopolar double bond

A simple rule for the occurrence of trans-h A distorted structures 2 at homopolar double bonds was derived from an elementary molecular orbital model treating a-jt mixing and a valence bond treatment . The relation between the singlet-triplet separation (A st) of the constituent ER2 and a +jt bond energy Ea+ was used as a criterion for determining the expected structure of R2E=ER2. The trans-b ai geometry 2 occurs when l/AEa+ < A sT < l/2Ea+n- The first part of the inequality determines the irawi-bending distortion of the double bond, while the second part determines the existence of a direct E=E link. 

In view of the very low reactivity of simple alkenes towards hydra-zoic acid, 2ind since these electron-withdrawing groups render the homopolar double bond less basic, it is unlikely that the reactions are Adfi in type. By comparison with hydrogen halide additions to such... 

The GO bond or the single C—O bond a constant characteristic value of the interatomic distance is obtained for a number of molecules Table LIII). The case of the double bond C=0 is rather different from that of the ethy-lenic bond G=C, since the C=0 bond is not homopolar and contributions from other valence bond structures, with a separation of charge and a different multiplicity of the bond, always occur. In aldehydes and ketones, for example, the structure > C+—0 contributes to the resonance of the molecule and in carbon dioxide the structure 0 —G O+ occurs. In Table LIV the internuclear. distances of this bond in various molecules is given. In aldehydes the GO bond distance is i-20 A and very probably the same distance occurs in ketones. In urea, because of the contribution of the structure... 

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