Amidines. Part 32. Influence of substitution at the amino nitrogen atom on the sensitivity to substitution at the imino nitrogen atom. pK_aValues of N¹-methyl-N¹-phenylformamidines in water–ethanol solutions

Abstract

A series of new N'-methyl-N1-phenylformamidines (RN=CH-NMeC,H,, 13 compounds) containing variable substituents at the imino nitrogen atom has been synthesized. The pK, values of the compounds have been measured in four binary ethanol-water solvents and correlated with Hammett-type substituent constants, and with pK, values of the corresponding primary amines determined in the same solvents. It is shown that substitution at the amino nitrogen atom has considerable influence on the sensitivity of the amidino group to the polar effects of substituents at the imino nitrogen atom. The parameters for both types of regression depend on the solvent.The equation for prediction of the pK, values for trisubstituted amidines, enabling explanation of changes in the p values for substitution at one site caused by substitution at the other two sites. is derived.

Study of hydrogen bonding and solvent polarity effects on the nitrogen NMR shieldings ofN,N-dimethylacetamidine

“…For example, Fourier transform ion cyclotron resonance spectrometry of the parent acetamidine gives a gas-phase proton affinity of 962.7 kJ mol 1 . 1 In the case of various alkylsubstituted formamidines, pK a values of about 9 have been measured, 2 and pK a values of about 13 have been reported for some N,N 0 -disubstituted amidines. 3 As shown by the resonance structures in Scheme 2, rotation around the C-NR 2 bond is restricted, the barrier being about 50-60 kJ mol 1 ( 13 C NMR measurements).…”

Directly-Observed β-Hydrogen Elimination of a Late Transition Metal Amido Complex and Unusual Fate of Imine Byproducts

“…The monomeric imine formed from β-hydrogen elimination in this case would be highly reactive and was not observed. Instead, the amidine PhNC(H)NMePh , was formed in 85% yield. This surprising product was clearly identified by comparison of 1 H NMR spectra, GC retention times, and MS data to an authentic sample prepared by addition of MeI to Li[PhNCHNPh].…”

Substituent Effects in the 13C-NMR Spectra of Six-Membered Nitrogen Heteroaromatic Compounds

“…Some support for this assumption was provided by study on relations between basicity and substitution [16][17][18][19][20] where it was shown that the polar effects of a substituent in a conjugated system can be considerably altered by changes of electron density in the system influencing transmission of these effects through the bonds.…”