The effect, on the energy increment for the first CH2 group, of changing the substituents on the central carbon atom of the first member of a normal alkyl series
Some years ago, Prosen, Johnson, and Rossini showed, from experimental enthalpies of combustion, the effect, on the energy increment for the first CH2 group, of changing the carbon and hydrogen substituents on the central carbon atom of the first member of a hydrocarbon normal alkyl series. The present authors have reviewed the experimental data on the enthalpies of combustion of the first several members of different normal alkyl series in which the central carbon atom of the end group may have attached to it atoms of nitrogen, oxygen, sulfur, chlorine, or bromine, as well as carbon and hydrogen. From these experimental data, the authors have evaluated the effect for the normal alkyl series in which the first member is the following, respectively: methane; ethane; methyl mercaptan, 2-thiapropane, and 2,3-thiabutane; methyl amine and dimethyldiazene; methyl bromide; propane, cyclopentane, and cyclohexane; methyl chloride; isobutane; ethene; methyl ether and methanol; propene and benzene; ethyne; acetaldehyde; formaldehyde. In the order given, the effect ranges from −(2.6 ± 0.4) to (8.9 ± 1.2) kcalth mol−1. (For propane, isobutane, and propene, in this series, the normal alkyl group is attached to the middle carbon atom.)