Antioxidant effectiveness of dehydrogenated p-phenylene diamines through NMR calculations

NMR shifts of N-phenyl-N’-alkyl-p-phenylenediamines (PPD) in vacuum were evaluated by B3LYP calculations using GIAO method. According to our previous studies, the Molar Antioxidant Effectiveness (AEM) of PPD antioxidants correlates with NMR chemical shifts of the amine nitrogen between aromatic rings (NA), the side aliphatic chain nitrogen (NB) and its neighboring tertiary carbon atom (CT) as well as of the hydrogens bonded to them. Our results indicate that the above mentioned chemical shifts correlate with increasing reactivity of dehydrogenated PPD antioxidants at these sites as well.

Geometry at the aliphatic tertiary carbon atom: computational and experimental test of the Walsh rule

The geometrical parameters of molecules of 2-substituted 2-methylpropanes and 1-substituted bicyclo[2.2.2]octanes were calculated at the B3LYP/6-311+G(d,p) level. They agreed reasonably well with the mean crystallographic values retrieved from the Cambridge Structural Database for a set of diverse non-cyclic structures with a tertiary C atom. The angle deformations at this C atom produced by the immediately bonded substituent are also closely related to those observed previously in benzene mono derivatives (either as calculated or as derived from crystallographic data). The calculated geometrical parameters were used to test the classical Walsh rule: It is evidently true that an electron-attracting substituent increases the proportion of C-atom p-electrons in the bond to the substituent and leaves more s-electrons to the remaining bonds; as a consequence the C—C—C angles at a tertiary carbon are widened and the C—C bonds shortened. However, this rule describes only part of the reality since the bond angles and lengths are controlled by other factors as well, for instance by steric crowding. Another imperfection of the Walsh rule is that the sequence of substituents does not correspond to their electronegativities, as measured by any known scale; more probably it is connected with the inductive effect, but then only very roughly.

Preparation of diamantanedicarboxylic acids with carboxyl groups on one secondary and one tertiary carbon atom

Bromination of 3-diamantanecarboxylic acid leads to a mixture of bromodiamantanecarboxylic acids which on Koch-Haaf carboxylation at high dilution affords a mixture of diamantanedicarboxylic acids with one carboxyl on the secondary and the other on the tertiary carbon atom of the diamantane skeleton. At low dilution, the Koch-Haaf carboxylation gives predominantly 3,9-diamantanedicarboxylic acid.