Cyclopropane bond lengths

The cyclopropane ring is necessarily planar, and the question of conformation does not arise. The C—C bond lengths are slightly shorter than normal at 1.5 A, and the H—C—H angle of 115° is opened somewhat from the tetrahedral angle. These structural... 

Conjugated chains, 14, 46 Correlation diagrams, 44, 50 Cyclobutadiene, 171 Cyclobutane, 47, 222 orbital ordering, 26 through-space interactions, 26 Walsh orbitals, 27 Cyclobutene, 200 Cyclohexane, 278 Cyclohexene (half-boat), 274 Cyclopen tadiene, 225 Cvclopen tadienone, 269 Cyclopentadienyl anion, 237 Cyclopentane, 254 Cyclopen ten e, 241 Cyclopropane, 41, 47, 153 construction of orbitals, 19, 22 Walsh orbitals, 22, 36, 37 Cyclopropanone, 48, 197 bond lengths, 38 Cyclopropen e, 49, 132 reactivity, 40... 

The above relationships between the thiiranes (20) and their dioxides (17) are reminiscent of those between cyclopropane and cyclopropanone. The entire phenomena of the C—C bond lengthening and the concomitant C—S bond shortening in the three-membered ring sulfones and sulfoxides can be accounted for in terms of the sulfur 3d-orbital participation and the variation in the donor-acceptor capacities of the S, SO and S02 . The variations of the calculated valence-state orbital energies, together with the corresponding variations of the C—C overlap populations, can be used to understand the discontinuous variations of the C—C and the C—S bond lengths in the series thiiranes -... 

The molecular structure of the parent compound was investigated in the vapor and in the solid phase using X-ray, XN and GED methods. The reported data are shown in Table 16. In both phases a clear bond length separation could be detected with a localized three-membered ring and its three adjacent double bonds. The symmetry-equivalent cyclopropane bonds are rather long in C3v-symmetric BUL (1.533-1.542 A), which can be explained by the common electron-withdrawing effect of the 7r-systems in a. svM-ciinal conformation. For comparison, the unaffected bonds in unsubstituted cyclopropane are 1.499 A in the crystal and 1.510 A in the gas phase. Therefore, the bond lengths in BUL... 

Accompanying this trend is a monotonic decrease in the internal angle at the adjacent position (P), from 119.6° in tetralin to 113.0° in cyclopropabenzene (Figure 16). The bond lengths at the ring fusion are demonstrably shorter in cyclopropabenzenes. This has caused some discussion of bond fixation in cyclopropabenzene however, parallel effects are seen for cyclopropane and cyclo-propene among cycloalkanes and cycloalkenes, respectively. Thus, the shorter bonds in cyclopropabenzene are expected or rationalized by simple rehybridization independent of any bond fixation. 

TABLE 9. Bond lengths (A) and bond angles (deg) in halogen-substituted cyclopropanes"... 

Calculations of the geometry of 106 have been reported by a number of groups238"243. The most accurate data are those from the calculations of Kraka and Cremer based on MP2/DZ+P and CCSD(T)/DZ+P calculations238. The C(l)-C(6) distance in the latter work was found to be 1.572 A, which is clearly longer than the value found for cyclopropane. The C(l)—C(6) bond order is significantly smaller than 1, indicating a partial bond between these atoms. 7t-Electron delocalization, as reflected by the ratio of calculated bond lengths [C(l)—C(2) 1.461, C(2)—C(3) 1.357, C(3)—C(4) 1.446 A], appeared to be... 

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