THE MOLECULAR-STRUCTURES AND CONFORMATIONAL COMPOSITIONS OF 1-BROMO-3-CHLOROPROPANE AND 1,3-DIIODOPROPANE, AS DETERMINED BY GAS-PHASE ELECTRON-DIFFRACTION AND MOLECULAR MECHANICS CALCULATIONS

The molecular structures and conformational compositions of 1-bromo-3- chloropropane (BCP) and 1,3-diiodopropane (DIP) have been studied by g as-phase electron diffraction at 27 and 38-degrees-C, respectively. BC P was found to exist as a mixture of the following four conformers, wi th estimated mole fractions in brackets: AA (0.1), AG (0.3), GA (0.1) and GG (0.5). These estimated mole fractions correspond to the followi ng relative conformational energies: DELTAE(AA) = 0.5 kcal mol-1, DELT AE(AG) = 0.3 kcal mol-1, DELTAE(GA) = 0.9 kcal mol-1 and DELTAE(GG) = 0.0 kcal mol-1. DIP was found to exist as a mixture of AA, AG and GG. The mole fractions and uncertainties estimated at 2sigma were found to be 0.05(9), 0.40(21) and 0.55(24), respectively. This corresponds to the following relative conformational energies: DELTAE(AA) almost-equa l-to 1.1 kcal mol-1, DELTAE(AG) = 0.7(6)kcal mol-1 and DELTAE(GG) = 0. 0 kcal mol-1. In order to conduct a more detailed investigation of the conformational geometries, results from molecular mechanics (MM) calc ulations have been included in the analysis.