Prepared froni 4-(2,6,6-trimcthylcyclohex-l-cnyl) -but-3-yn-2-01 acetate by epoxidation followed by lithium aluminium hydridc reduction: NMR. (CDCI,) : 1.04(3H, s). 1.20(3H, s ) , 1.27(311, d, J = ~H z ) , 1.34(3H, s), 4,36(1H, q, ,I = 7 Hz), 5,46(1H, d x d , J = 7HZ, J' -5112) ppni; IR. (liq.): 3350, 1955 cm-l.Summary. The literature data on hcteropolar and homopolar 2-center bond dissociation energies in organic molecules in the gas phase and the corrcsponding heats of formation of radicals and ions havc been critically evaluated. Data for more than 500 bonds are represented in tabular form together with the pertinent literature references.Selected electron affinitics and n-bond dissociation energies have also bccn incorporated. The follow-up paper will discuss some cmpirical general aspects of these data particularly regarding the effect of structure on the bond dissociation energies.