A brief analysis is presnted of the current understanding of substituent perturbations in monosubstituted benzenes as determined by substituent induced carbon chemical shifts. A critical tabulation of the four substituent chemical shifts is given for c. 700 monosubstituted benzenes.

13C substituent effects in monosubstituted benzenes

The doubly-bridged iron(II)-tetraphenylporphyrin derivative 6, carrying a sterically fixed S− ligand in the ‘proximal’ position and the substrate at the ‘distal’ site, was synthesised as an enzyme model for cytochrome P-450. Compound 36, the CO complex of 6, displays a split Soret band (403 and 457 nm) similar to the native cytochrome P-450.

Synthetic Models of the Active Site of Cytochrome P-450. 1st Communication. The Synthesis of a Doubly-Bridged Iron(II)-Porphyrin Carrying a Tightly Bound Thiolate Ligand†

A Direct and Mild Conversion of Tertiary Aryl Amides to Methyl Esters Using Trimethyloxonium Tetrafluoroborate: A Very Useful Complement to Directed Metalation Reactions

Carbon-13 NMR spectra are reported for 63 substituted benzonitriles in deuteriochloroform or in its mixture with dimethyl sulphoxide-d6. The substituent-induced chemical shifts (SCS) of the CN carbon correlate well with dual substituent parameters (DSP) in the para series but poorly in the meta series, whichever parameters are used. The DSP treatment was found to be inferior to principal component analysis (PCA), using as a probe 29 sets of literature data on α,β-unsaturated benzene derivatives. Whereas one component is sufficient for meta derivatives, two terms are needed for para derivatives, which are different for the α- and β-positions. The constants derived by PCA could be in principle used to predict further SCS, but their scope must be still explored.

Correlation of carbon‐13 substituent‐induced chemical shifts revisited: Meta‐ and para‐substituted benzonitriles

Ferrocene Linked to PtL2 Fragments (L2 = Cl2, Fumaronitrile, 3,6-Di-tert-butylcatecholato): A Spectroscopic and Theoretical Investigation of Redox Behavior and Charge Distributions†

All carbon-13 chemical shifts for 11 para-substituted N,N-dimethylbenzamides in 1 mole % chloroform solution are reported, with assignments based upon double resonance experiments, analogy to chemical shifts of benzamide, and self-consistency between experimental and calculated values using recognized substituent parameters. In contrast to earlier reports, the aryl carbon chemical shift assignments for N,N-dimethylbenzamide are C-2, 127.0; C-3, 128.7; C-4, 129.4, and for p-chloro-N,N-dimethylbenzamide are C-1, 134.6; C-4, 135.5 ppm, relative to internal TMS. Good Hammett correlations (σp) are reported for 13C chemical shifts of C-1 (σ = 11.9 ppm) and even for the carbonyl group (σ = −2.3 ppm) but are markedly improved if correlated with σp+ (σ = 9.5 ppm) and Dewar's F (σ = −1.9 ppm), respectively. Excellent Swain–Lupton F and R correlations were found for some of the 13C chemical shifts and yielded values for percent resonance contributions to transmission of substituent effects as follows, C-1, 75 ± 4%; C-2, 51 ± 3%; CO, 31±2%. These are compared to similar values calculated from the CO of benzoic acids of 34±10%, and from the nitrogen-15 chemical shifts of benzamides of 56±2%. Correlations of these 13C δ values and 15N δ values with rotation barriers (ΔG) for N,N-dimethylbenzamides were examined, and it was found that while CO δ values correlated only poorly the C-1 δ values correlated very well, but the best correlation was for 15N δ values of benzamides. It is suggested that Δ G and δ 15N are intrinsically related due to their numerical correlation, and the close similarity in percent resonance contribution of substituent influence on these parameters.

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

Correction. Infrared Spectra dn Transmission of Electronic Effects in Substituted Phenyl N,N-Dimethylcarbamates and S-Phenyl N,N-Dimethylthiocarbamates

Joyce M. Wilkins

Papers

Carbon-13 NMR spectra of a series of para-substituted N,N-dimethylbenzamides. Comparisons of linear free energy relationships for carbon-13 and nitrogen-15 chemical shifts and rotation barriers

Correction. Infrared Spectra dn Transmission of Electronic Effects in Substituted Phenyl N,N-Dimethylcarbamates and S-Phenyl N,N-Dimethylthiocarbamates