Effect of Intramolecular Hydrogen Bonds on the Gas-Phase Basicity of Guanidines

Abstract

Three series of novel trisubstituted guanidines containing at least one hydrogen bond accepting (HBA) group were modelled using B3LYP/6–311+G(2df,p)//B3LYP/6–31G(d) calculations. Their structure was modified by incorporating a variety of different HBA groups covering a wide range of hydrogen bond strengths. Calculated gas-phase basicities (GBs) ranged from 1035 to 1181 kJ mol–1 depending on the nature of the substituent. To rationalise changes in the GB, a correlation of GB against two independent variables (pKHB and σ4B) was conducted where pKHB served as the descriptor of the hydrogen bond strength and σ4B was introduced to describe changes in the GBs in the open-chain model systems, i.e. in the absence of intramolecular hydrogen bond (IMHB), caused by the electronic effect of the propyl-HBA substituent. A very good correlation of the calculated gas-phase basicities against these two independent variables was established for all three sets of the bases.

Experimental Basicities of Phosphazene, Guanidinophosphazene, and Proton Sponge Superbases in the Gas Phase and Solution

“…Many new classes of nonionic superbases have been designed, and many of them have been prepared during the past decade. Among these are guanidinophosphazenes, − various types of proton sponges, − superbasic guanidine derivatives, ,,− macrocyclic proton chelators, , chiral phosphazenes, ,− quinones, phosphonium ylides, ,, azaphosphatranes, , carbenes, ,,− etc. ,− Theoretical calculations predict that many of these bases are more basic than the most basic experimentally measured compoundP 2 -phosphazene EtP 2 (dma) 5 (dma = dimethylamino; see Chart for its structure; GB = 264 kcal mol –1 ) …”

Computational study of substituent effects on the gas‐phase stabilities of N‐phenylguanidinium ions

“…Guanidinium ions are interesting not only as cations of ILs but also as conjugate acids of basic organocatalysts utilized in organic syntheses, functionalized molecules, and so on . It will be greatly appreciated if the fundamental investigation presented in this work contributes to such applied fields in guanidinium chemistry.…”

Computational Study of Electronic Influence of Guanidine Substitution on Diels-Alder Reactions of Heterocyclic Dienes

“…As the part of our program in quantum-chemical studies of mechanisms of cycloaddition reactions of heterocycles such as furan, [7] pyrrole, [8] siloles, germoles, [9] isobenzofurans [10] and basicities of guanidines, [11] we have turned our attention to the synthetic utility of cycloaddition reactions to deliver guanidine compounds anchored on the polycyclic scaffolds. Synthetically powerful way to achieve this objective is the employment of Diels-Alder reaction.…”