** Authors:**
EMAD A. S. AL-HYALI

** Abstract: **
Two sets of additive parameters used previously for the
calculation of C-13 chemical shifts of mono and poly six-membered
cycloalkanes were applied for the prediction of N-15 chemical shifts
of some methyl piperidine derivatives. These sets are based on 2
principles: the p-character (substituents electronic effect) of the
atom under consideration and the steric effect that reflects the
spatial arrangement of the molecule. An additional parameter, namely
the ring angle of the studied atom, was added to the other parameters
to define the structural distortion that is due to large steric
interactions.
The p-character in set (1) is represented by the number of carbon
atoms; primary, secondary, tertiary, and quaternary types at \alpha
-position to the nitrogen, while in set (2) it is introduced as the
partial electronic charge. The steric effect is expressed in terms of
the actual number of the interacting proton-proton and/or proton-lone
pairs in both sets. Quantum mechanical and regression analysis
methods were employed for this investigation.
The results showed that both sets were good for the prediction of N-15
chemical shifts. The parameters of set (2) were more consistent with
the theory of nuclear magnetic resonance (NMR) spectroscopy;
therefore, they are considered for further research. The study also
included derivation of a common set of parameters for the calculation
of C-13 and N-15 chemical shifts of cyclic systems. The derived
parameters were tested by the estimation of the chemical shifts of
other systems. Deviations were observed only in positions that were
involved in large steric interactions.

** Keywords: **
N-15 chemical shift, Additive parameters, Regression analysis

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