SUBSTITUENT EFFECTS ON N-15 AND O-17 CHEMICAL-SHIFTS IN NITROBENZENES - CORRELATIONS WITH ELECTRON-DENSITIES
SUBSTITUENT EFFECTS ON N-15 AND O-17 CHEMICAL-SHIFTS IN NITROBENZENES - CORRELATIONS WITH ELECTRON-DENSITIES
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DOI：
10.1021/jo00158a006
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发表时间：
1983-01-01
影响因子：
3.6
通讯作者：
BROWNLEE, RTC
中科院分区：
文献类型：
--
作者：
CRAIK, DJ;LEVY, GC;BROWNLEE, RTC
15N and 170 NMR spectra have been measured for a series of para-and meta-substituted nitrobenzenes, and the derived substituent chemical shifts (SCS) have been correlated with oi and< rR substituent constants by using the dual substituent parameter (DSP) equation. The polar nature of the substituent is most important in determining the nitrogen chemical shifts, which follow a “reverse” trend; ie, electron-withdrawing substituents induce upfield 15N shifts. This observation is consistent with a ir-polarization mechanism in which the N= 0 bonds are polarized by the dipole of the substituent. The proposal that this mechanism is transmitted through space and is not dependent on conjugation between the substituent and side-chain nitro group is confirmed by the observation that substituent effects on 15N SCS values are~ 25% larger in themeta series compared with the para series. Substituent chemical shifts at theoxygen atom are an order of magnitude larger than those at nitrogen and depend strongly on both polar and resonance substituent effects. The 170 shifts follow a normal direction (ie, donor substituents induce upfield shifts) and are smaller in the meta series than in thepara series. Calculated ab initio ir-electron densities reproduce the 16N and 170 chemical shift trends.
