Analysis of substituent effects on the carbon-13 and oxygen-17 NMR chemical shifts of some phenylthiophen-2′-ylmethanones by linear free energy relationships
✍ Scribed by Renato Noto; Michelangelo Gruttadauria; Stefano Chimichi; Giovanni Petrillo; Domenico Spinelli
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 88 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
The 13 C chemical shifts of the title compounds (1) were determined in CDCl 3 and in CD 3 OD as well as in D 2 SO 4 solutions. Moreover 17 O chemical shifts of 1 in CDCl 3 were measured. The SCS (substituent-induced chemical shift) values were analyzed by means of linear free energy (LFE) relationships and also by crosscorrelations with those of both the corresponding 5-substituted 2-acetylthiophenes (2) and 4-substituted acetophenones (3). The 13 C SCS values indicate a transmission pattern of the substituent effect which is more complex than those observed in 2 and 3. On the other hand, the 17 O SCS values are more significant and reliable indicators of the transmission of the electronic effects on to the carbonyl group of 1, clearly underlining the different propensities of the phenyl and the thiophen-2'-yl groups in accomplishing such a transmission. Some apparent discrepancies observed between protonation and 17 O NMR data of compounds 1, 2 and 3 are also discussed.