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Paper Information

Journal:   IRANIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING (IJCCE)   2002 , Volume 21 , Number 1; Page(s) 6 To 12.
 
Paper: 

2H ISOTOPE EFFECT ON 13C CHEMICAL SHIFTS OF NITRO- BENZO-9-CROWN-3

 
 
Author(s):  MOGHIMI A.*, RASTGAR M., GHANDI M., BIJANZADEH H.R.
 
* CHEMISTRY DEPARTMENT, UNIVERSITY OF IMAM HOSSEIN, TEHRAN, I.R. IRAN
 
Abstract: 

Deuterium substitution on two ortho-substituted –OCH2 fragments in Nitro-Benzo-9-Crown-3 induces low frequency shifts, positivemn DCj, in all13 C NMR resonances which are an indication of the increased shielding in this crown ether. The magnitude of these shifts vary from 15DC7=716 to 54DC3=15 ppb for C7 and C3 carbons directly attached to 2H, respectively. The influences of concentration and solvent, CDCl3, CD3COCD3, and C6D6, on mn DCj values were investigated. The mn DCj values depended more on the nature of the solvent than on the concentration.

The order of induced isotope shifts is: 15D, 51D> 24D, 42D > 34 D>, 43D> 56D, 65D> 45D, 54 D. The isotope shifts observed are suggested to be a sum of contributions from low frequency shift due to inductive-type and negative hyper conjugation perturbations. The C-D bond, as a poorer electron acceptor than a C-H bond induces less positive charge on directly attached oxygen's O1 and O2. This, in turn, causes shielding of C1 and C2 in C1O1CD2 and C2O2CD2 fragments. The difference in 34DC1 and 43DC2 values is attributed to the conformational dependence of the negative hyper conjugation. The C1 and C2 are in fact, not equally affected by the two CD2 groups by negative hyperconjogation because of the existence of NO2 group attached to the benzene ring.

 
Keyword(s): NMR, L3C NMR, 2H ISOTOPE SHIFT, 2H ISOTOPE LABELING, CROWN ETHERS, NITRO-BENZO-9-CROWN-3
 
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