Resources, Structures, and Conformations of Natural Products

Covalent bonds in biological carbon compounds vary in length from 0.96 (OH) to 1.54 A (CC). In other words the variability is not more than 20%. The median length is about 1.25 A (Table 1.2.1). Longer bond lengths are only found in nonbiological bonds (e.g. 2.14 A in Cl) or in metal complexes and oxides (e.g., 2.1 AinFe(II)O). 

The bond angles of carbon-carbon bonds rise with the multiple bond character. The angle is 109° for single bonds, and somewhat larger for double bonds (120°). It disappears in the triple bond (180°), which does not occur in common 

Covalent bond energies are close to 100 kcal/mol in single bonds, 150 kcal/mol in double bonds, and 200 kcal/mol in triple bonds in natural compounds (Table 1.2.2). Hetero atom-hetero atom single bonds (e.g., in hydrazine, peroxides, disulfides, and elementary halogen molecules) have bond energies of less than 50 kcal/mol. They tend to homolyze spontaneously, giving two radical moieties with an unpaired electron each. 

Thermal energy is expressed in kcal/mol or is multiplied by a factor of 4.2 to yield kJ/mol. Electrical energy is given in electron volts (eV), which is directly connected to the electrochemical potential in volt (V) for one-electron transfers. The volt scale of electrochemistry is connected to the hydrogen electrode, which differs from the electrical eV scale by a constant of 4.5 V. This difference is, however, of no 

One mole of light quanta corresponding to a wavelength of 500 nm (= 20,000 cm ) contains the same energy as 1 mol of a one-electron redox pair with a potential difference of 250 mV and may cleave one mol of a molecular complex with a bond energy of 58 kcal/mol. 

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