Bond Lengths in Hydrocarbons

Carbon-carbon bond lengths in hydrocarbons depend both on the formal bond order (single, double, triple) and on the detailed environment. 

Measure and record the carbon-carbon bond lengths in ethane, ethene and ethyne. These will serve as standards for single, double and triple bonds, respectively. 

Is the double bond incorporated into allene significantly shorter, significantly longer or about the same length as the bond in ethene Draw a Lewis structure for allene to justify your conclusion. 

Measure the carbon-carbon bond length in benzene. Would you describe it as a single bond, a double bond, or somewhere in between Draw whatever resonance contributors are needed to justify your conclusion. 

Are the carbon-carbon bond distances in allyl cation, allyl radical allyl anion all similar, or are they significantly 

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Thus there appears to be no average bond length deformation beyond experimental error (2-0 esd). Only two of the bonds deviate from their counterparts by more than 3 esd (4-6 esd in both cases). The conclusion from this example is that crystal packing does not influence bond lengths in hydrocarbons much, if at all, at current levels of accuracy of measurement. 

Fig. 25. Linkage bond lengths in hydrocarbons containing less strain.

Electronic Digital Computers to Molecular Orbitd Problems. I. The Caloiladon Bond-Lengths in Hydrocarbons. 

Limiting (6-311+G basis set) Hartree-Fock bond lengths in the compounds examined are consistently shorter than experimental distances, the same result as seen for multiple bonds in hydrocarbons. Results obtained using the 6-31G basis set are nearly identical, which suggests that the 6-31G model closely reflects the Hartree-Fock limit insofar as bond length calculations for these types of systems. 

Bond Lengths in Aromatic Hydrocarbons.—As on example of the use of the single-bond double-bond resonance curve of interatomic... 

Kiralj, R. and Ferreira, M.M.C. (2002) Predicting bond lengths in planar benzenoid polycyclic aromatic hydrocarbons a chemometric approach. J. Chem. Inf. Comput. Sci., 42, 508-523. 

The first class contains all those molecules for which the excitation energy of the alkali atom, , is lower than the difference between the ioniza-tion energy I and the electron affinity (M) of the molecule [ < / - (M)], and where in addition the change in bond length in going from MtoM is very small (<0-l A). Examples are N2, 02, NO, CO, SOz, C02, the unsaturated hydrocarbons, and the olefinic and aromatic hydrocarbons. In all... 

Initially, the a-bond energies were adjustable parameters to fit heats of formation for selected compounds. In the improved treatment of hydrocarbons, they were calculated directly as a function of the bond length. In this way a smaller value of 20 kcal/mol was obtained for the resonance energy of benzene. It... 

A and rzj = 1.47 A. Rather good agreement has been reported between calculated and experimental bond lengths in polynuclear aromatic hydrocarbons. Typical results are shown on the next page for naphthalene and anthracene (with... 

Bond numbers and bond lengths in tetrabenzo de, no, st, cj, dj) heptacene and other condensed aromatic hydrocarbons a valence bond treatment. Acta Cryst. B36 (1980) 1898-1901. 

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