Bonding Studies in Group IV Substituted n,n-dimethylanilines Page: 2
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and p-trimethylgermyl groups are electron-withdrawing sub-
stituents. Further data which indicate this electron-with-
drawing effect in the ground state are the observed hyperfine
splitting constants of the radical cations of p-trimethyl-
silyl-N,N-dimethylaniline and p-trimethylgermyl-N,N-dimethyl-
aniline. These hyperfine splitting constants are larger
than those of the p-tert-butyl-N,N-dimethylaniline radical
cation, behavior typical of electron-withdrawing groups.
The absence of d-orbital overlap with the ring tr-system
found in CNDO/2 calculations suggests that djfpff bond formation
can not account for the stabilization of the highest-filled
molecular orbital observed in p-trimethylsilyl-N,N-dimethyl-
aniline. In addition the CNDO/2 results show that there is
significant overlap between the silicon p-orbitals and ring
carbon pff-orbital, a large amount of silicon d-orbital electron
density, and a significant charge build up on the methyl carbon
atoms of the trimethylsilyl group* This bonding description
is consistent with a cr-tT interaction in the ground state.
The energies of the low-lying excited states were deter-
mined from a correlation of the ultraviolet spectra with the
ground state energies. Excited states where strong conjugation
between the ring tr-system and either a trimethylsilyl or
trimethylgermyl substituent is possible show stabilizations
of approximately 0.20eV relative to those of N,N-dimethyl-
aniline. On the basis of the favorable energy match between
the group IV metal empty d—orbitals and these excited states
the observed stabilizations are attributed to djr-pjy*bonding.
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Drews, Michael James. Bonding Studies in Group IV Substituted n,n-dimethylanilines, dissertation, December 1971; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc164513/m1/3/: accessed December 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .