Nitromethane ionic structure

The pale yellow colour of nitrobenzene or p- nitrotoluene turns more intense when the compound is dissolved in sulphuric acid, while solutions of nitromethane and other nitroparaffins are colourless. The yellow colour of the aromatic nitro compounds is due presumably to an ionic structure containing a quinonoid ring. 

In contrast to catalysts 37-39, which are neutral species with dual hydrogen bond donor capability, catalysts such as 40-43 are ionic displaying a hydrogen bond donor site that better resemble the proton (H" ), which is probably the most common Lewis acid found in Nature. The pioneering work carried out by Johnston showed the effectiveness of the chiral proton-based structure 40 in the addition of nitromethane and nitroethane to aryl N-Boc imines (Scheme 29.22) [48]. As a... 

QM/MM calculations and experimental kinetic study have explored the effects of solvation on the transition states for reaction between nitromethane and formaldehyde and between nitropropane and benzaldehyde. Asymmetric reactions of nitromethane with various aldehydes have been promoted by Cu(II) coordinated with amino alcohols, 0 imidazolium/pyrrolidinium-tagged Indabox, and imidazolium-taggedbis(oxazoline)-based chiral ligands. The Henry reaction has also been promoted by Mn(OAc)2/Schiff bases bearing a triazole structure, with up to 99% yield, and by phosphonium ionic ligands MeP+(octyl)3 R0C02 without solvent. ... 

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