Nitriles with High Gas-Phase Basicity—Part II Transmission of the Push–Pull Effect through Methylenecyclopropene and Cyclopropenimine Scaffolds Intercalated between Different Electron Donor(s) and the Cyano N-Protonation Site

Abstract

This work extends our earlier quantum chemical studies on the gas-phase basicity of very strong N-bases to two series of nitriles containing the methylenecyclopropene and cyclopropenimine scaffolds with dissymmetrical substitution by one or two electron-donating substituents such as Me, NR2, N=C (NR2)2, and N=P (NR2)3, the last three being strong donors. For a proper prediction of their gas-phase base properties, all potential isomeric phenomena and reasonable potential protonation sites are considered to avoid possible inconsistencies when evaluating the energetic parameters and associated protonation or deprotonation equilibria B + H+ = BH+. More than 250 new isomeric structures for neutral and protonated forms are analyzed. The stable structures are selected and the favored ones identified. The microscopic (kinetic) gas-phase basicity parameters (PA and GB) corresponding to N sites (cyano and imino in the cyclopropenimine or in the substituents) in each isomer are calculated. The macroscopic (thermodynamic) PAs and GBs, referring to the isomeric mixtures of favored isomers, are also estimated. The total (pushing) substituent effects are analyzed for monosubstituted and disubstituted derivatives containing two identical or two different substituents. Electron delocalization is examined in the two π–π conjugated transmitters, the methylenecyclopropene and cyclopropenimine scaffolds. The aromatic character of the three-membered ring is also discussed.

Synthesis, Thermal, DFT Calculations, HOMO-LUMO, MEP, and Molecular Docking Analysis of New Derivatives of Imidazolin-4-Ones

“…Gauss View 5 software was used to visualize the output files [21]. The structural properties of compounds 1a-c and 2a-c were determined by applying Becke's threeparameter hybrid functional (B3) for the exchange part and the Lee-Yang-Parr (LYP) correlation function [22] with 6-31G(d,p) level in order to obtain the optimized geometrical parameters of the compound. The MEP and HOMO-LUMO energies were calculated at the same level.…”

On Analogies in Proton-Transfers for Pyrimidine Bases in the Gas Phase (Apolar Environment)—Cytosine Versus Isocytosine

“…The relative quantities (∆E, ∆H, T∆S, and ∆G) have been calculated separately for ionic isomers of mono-anions (ABH) − , di-anions (AB) 2− , mono-cations (AH 2 BH) + , and di-cations (AH 2 BH 2 ) 2+ . The composition of the neutral and ionic isomeric mixtures of C and iC have be estimated on the basis of ∆G i calculated for individual neutral and ionic isomers using equation (1), where x i is the isomer mole-fraction [51][52][53][54]. Note that ∆G i can be different for neutral and ionic isomers, and thus the calculated x i cannot be the same for ionic and neutral species.…”

Strong Bases and beyond: The Prominent Contribution of Neutral Push–Pull Organic Molecules towards Superbases in the Gas Phase

“…Isomeric (rotational and/or prototropic) states of neutral and protonated forms and also the favored sites of protonation in the other derivatives given in Figure 3 ( HA , Agm , AEP , FDMEP , BG , M , I , and nitriles) have been analyzed by us at various DFT and/or MP2 levels over the last 20 years [ 69 , 70 , 71 , 72 , 73 , 74 , 75 ]. For HA , AEP , and FDMEP , their GB values were also determined by FT-ICR equilibrium measurements (960.3, 954.8, and 1008.8 kJ mol −1 , respectively, evaluated in Ref.…”

“…The experimental GBs of Me 2 N–CH=N–C≡N (857.3 kJ mol −1 ) and Me 2 N–CH=CH–C≡N (864.3 kJ mol −1 ) are higher than that of NH 3 (819.0 kJ mol −1 ) but close to that of MeNH 2 (864.5 kJ mol −1 ) [ 9 ]. On the other hand, detailed theoretical studies for various series of push–pull nitriles with guanidino and phosphazeno groups linked directly to the cyano-C atom or separated by a resonance transmitter indicated that it is possible to extend the GB scale for nitriles up to 1100 kJ mol −1 [ 74 , 75 , 100 , 101 ]. The calculated strong electron donating effects of pushing groups may serve as a guide for preparation of nitrile superbases.…”

“…Investigations revealed that the gas-phase pushing effect (defined as δPA = PA(D–C≡N) − PA(H–C≡N)) of the Me 2 NCH=N– group in Me 2 NCH=N–C≡N is stronger than that of Me 2 N– in Me 2 N–C≡N ( Figure 10 ). Then, very strong gas-phase pushing effects of guanidino and phosphazeno substituents, directly attached to the cyano C atom or separated by a π-electron transmitter, were estimated by DFT and/or G n computations [ 74 , 75 , 100 , 101 ]. In all derivatives, the cyano N-sp atom is the favored site of protonation.…”