Trans-7-tetradecene
This molecule was partially transformed (30%) into the corresponding
trans-epoxide with 13C signals at 59 at 26 ppm
(Figure 4, Table 1 ) during auto-oxidation. Clearly the olefin
decreased while the epoxide increased. This removes any doubt about the
formation of epoxides alpha to the olefin, often proposed in the
literature. This observation, based on changes in NMR signal intensities
(Table 1 ), was confirmed by HMBC NMR (vide sotto). The methine
carbon and hydrogens of the epoxide are not adjacent to an olefin. Thus,
if these species form at 210°C, they are short lived intermediates
absent in solutions analyzed at 25°C.
Minor 13C NMR peaks (between 155 and 215 ppm), from
higher oxidized species (aldehyde, ketone, acid) are also present.
Transformation of olefinic carbons into carboxylic and aldehyde carbons
reveals fragmentation.
DOSY shows no species with largely reduced D compared to untreated
trans-7-tetradecene (Table 2 and Figure S5) which diffuses at D
= (7.8 ± 0.1) x 10-10 m2/s,Figure S 7 . After partial oxidation, the trans-7,8-epoxide
produced, with its 1H signal at 2.6 ppm, diffuses
somewhat slower D = (4.8 ± 0.1) x 10-10m2/s than unreacted trans-7-tetradecene in the mixture
(6.2 x 10-10 m2/s) (Figure
5 ).