Double bond, electronic structure length

Recent calculations did further reveal that also the length of a finite nanotube has essential influence on its structure, which may adopt one out of three basic variants The Kekule-structure, the incomplete, and the complete Clar-structure (Figure 3.8). The first does not contain isolated double bonds, but is rather completely conjugated. The Clar-structures both feature p-phenylene moieties which, in the case of the incomplete Clar-structure, are flanked by isolated double bonds. This structural variety causes differences in electronic properties and thus in the... 

However a similar effect should then be observed in CI-CH2-CN, since the CN group is also strongly electron-attracting. Instead, the C-Cl bonds in Cl-CH3 and CI-CH2-CN are of essentially the same length [46]. Furthermore, the C-Cl bond was found to be weaker in CI-CH2-NO2 than in CI-CH3, by about 7 kcal/mol, which is not consistent with its having acquired some double bond character (structure 5). 

Examine the geometry of porphin. Is the molecule planar Does the molecule incorporate explicit single and double bonds (as in the structure above) or bonds of intermediate length How many % electrons are involved in porphin s central ring Is poiphin aromatic Elaborate. 

The question of electronic conductivity in the polyphosphazenes inevitably raises questions regarding the electronic structure of the phosphazene linkage.7-12 This matter has been the subject of controversy in the literature, but experimentally the situation is now well known.4,13 In spite of the fact that the phosphazene backbone is fully conjugated, bond equalized and possesses bond lengths which are indicative of partial double bond character, the evidence suggests that these are localized systems. 

There are many other molecules in which some of the electrons are less localized than is implied by a single Lewis structure and can therefore be represented by two or more resonance structures. For example, the three bonds in the carbonate ion all have the same length of 131 pm, which is intermediate between that of the C—O single bond in methanol (143 pm) and that of the C=0 double bond in methanal (acetaldehyde) (121 pm). So the carbonate ion can be conveniently represented by the following three resonance structures ... 

In an early electron diffraction investigation of the structure of 2-methylpropene (isobutylene), Bartell and Bonham (1960) found that the three terminal carbon atoms are arranged in an almost perfect equilateral triangle around the central carbon despite the considerable difference in the single and double bond lengths (Figure 5.4). This result led Bartell to suggest that the terminal carbon atoms are close-packed around the central carbon atom. He then... 

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