Strahlungschemie von Kohlenwasserstoffen. 19. Mitteilung . Die Deuteriumabspaltung in isotop‐isomeren Cyclohexanen

The G ‐value for D 2 production has been measured for C 6 D 12 and for gem‐, cis‐ , and trans ‐C 6 H 10 D 2 . The G ‐values for the unimolecular process are 0.24, 0.023, 0.010 and 0.004, resp. In C 6 D 12 two bimolecular processes can be distinguished: one includes ‘hot’ D‐atoms, e. g. a species that shows no isotope effect for the hydrogen abstraction yielding D 2 and HD, resp.; its G ‐value is 1.22. The other process goes via thermal D‐atoms, it has a G ‐value of 1.97 and gives an isotope effect for abstraction: k D / k H = 0.075 (10°C). In the partially deuteriated cyclohexanes, only the former process can be observed. Its G ‐value depends on the irradiation temperature and phase, is independent of the position of the D‐atoms in the molecule and amounts to 0.035 (10°C), 0.028 (−40°C solid), 0.040 (−40°C liquid with 25% hexane). The following conclusions can be drawn: the unimolecular detachment shows no intramolecular isotope effect in partially deuteriated molecules and comes only from the gem‐, cis‐ and trans ‐positions. Most of the G ‐values for the D 2 and HD production by different reaction paths can be cross‐checked by G ‐values from different mixtures. The agreement between these values is excellent.