Formamide, protonated

Note, that both urea and formamide actually protonate on oxygen rather than on nitrogen. 

Rearrangements closely resembling the Stevens rearrangement have been investigated by applying Grignard reagents or potassium t-butoxide in dimethyl-formamide (low availability of protons) to cis- and trans-2,4-diphenylthietane oxides and dioxides . The main results are summarized in equation 97 and 98. 

This type of charge reduction by charge transfer to the solvent molecule occurs in general when SI are polar solvent molecules of aprotic character such as dimethyl-sulfoxide, dimethyl formamide, and acetonitrile. Protic solvents such as water lead to charge reduction which involves an intracluster proton transfer reaction ... 

Finally, it s worth mentioning the formamide group. Although this looks like a special case of a secondary amide, rotamers of different intensity are often seen. Compounds with a formamide attached to an aromatic ring can give particularly complex spectra. Not only does the NH proton couple to the CHO proton, with a coupling of about 2-3 Hz in the cis isomer, and 8-9 Hz in the trans isomer, but, any aromatic protons ortho to the formamide are also split out in the rotamers ... 

Mistryukov, E. A. et al., Mendeleev Comm., 1993, (6) 242 Adding formamide to a reaction mixture of allylzinc bromide and a ketone as a proton source for a Barbier reaction in ether or tetrahydrofuran gave uncontrollable explosion-like reaction. The reaction proceeded smoothly when starting from zinc dust and allyl bromide, with both formamide and the ketone in situ. 

Protons on carbon geminal to -NCS or -NHCHO functions do not experience the weak coupling with nitrogen due to the normal hybridization of the nitrogen atom. In the case of formamides, however, both E- and Z-rotamers are possible as revealed by resonances in the H NMR spectrum. 

A minor isonitrile named acanthellin-2 with a specific rotation of — 24.1° was reported with no further details except some IR and MS data [3]. Isothiocyanate 15 and formamide 16 were also isolated from Axinella cannabina in a later study, in which isonitrile 14 and isomers 17-19 were also secured [35]. That 17-19 are C4(14)-ene isomers of 14 was concluded after extensive double resonance H NMR experiments. Coupling constants and nOe effects between the affected protons and various substituents of 17 established the relative stereochemistry of this series. 

Hindered rotation can separate the NMR signals of apparently equivalent protons. This causes changes in the geometry of the molecule. This fact is illustrated by C - N bond if N, N dimethyl - formamide which has partial double bond character due to resonance stabilization of the molecule ... 

The synthetic interest in direct substitution of protonated heteroaromatic bases by carbamoyl and a-amidoalkyl radicals arises because the reaction is applicable to a variety of heteroaromatic bases having highly reactive nucleophilic positions and because a variety of amides can be used. The selectivity of attack is complete at the a- and y-positions of the heterocyclic system owing to the nucleophilic character of both carbamoyl and a-amidoalkyl radicals, The results with formamide are shown in Table VI. Quinoline with dimethylformamide gave a variety... 

Nitrobenzene radical-anion is more stable in aprotic solvents than its aliphatic counterparts. Nitrobenzene shows two one-electron polarographic waves in acetonitrile with By, -1,15 and -1.93 V vj. see, Tire first wave is due to tlie formation of the radical-anion and this species has been characterised by esr spectroscopy [6]. Nitrobenzene radical-anion can also be generated in steady-state concentration by electrochemical reduction in aqueous solutions at pH 13 [7] and in dimethyl-formamide [8]. It is yellow-brown in. solution with A., ax 435 nm. Protonation initiates a series of reactions in which niti osobenzene is formed as an intermediate and... 

Arylimines (68) in a protonated form are reduced by sodium cyanoborohydride to V-arylcyano-formamides <92MI4ll-0l>. 

Organic solvents can also be classified according to their ability to accept or transfer protons (i.e., their acid-base behavior) [20,21]. Amphiprotic solvents possess donor as well as acceptor capabilities and can undergo autoprotolysis. They can be subdivided into neutral solvents that possess approximately equal donor and acceptor capabilities (water and alcohols), acidic solvents with predominantly proton donor properties (acetic acid, formic acid), and basic solvents with primarily proton acceptor characteristics (formamide, N-methylformamide, and N,N-dimethylformamide). Aprotic solvents are not capable of autoprotolysis but may be able to accept protons (ACN, DMSO, propylene carbonate). Inert solvents (hexane) neither accept nor donate protons nor are they capable of autoprotolysis. 

L = dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), and triphenylphos-phine oxide (OPPh3). The former illustrates how simple polyethers may stabilize the hydrated dioxomolybdenum(VI) bromide core. The others are representative examples of addition compounds with ligands that are able to displace water from the coordination sphere of molybdenum but at the same time are not sufficiently basic toward the proton to cause formation of hydrobromides and molybdates. 

Solvent effects Different solvents have different effects on the nucleophilicity of a species. Solvents with acidic protons are called protic solvents, usually O—H or N—H groups. Polar protic solvents, e.g. dimethyl sulph-oxide (DMSO), dimethyl formamide (DMF), acetonitrile (CH3CN) and acetone (CH3COCH3) are often used in 8 2 reactions, since the polar reactants (nucleophile and alkyl halide) generally dissolve well in them. 

In fact, this interpretation became imperative when it was found that lithium perchlorate in dimethyl formamide does not initiate the polymerisation in systems for which lithium chloride is an effident initiator. This proves that the reaction involves the negative ion, i. e. Cl- or CJ04, and not the positive Li+ ion, and while CT in dimethyl formamide is a sufficiently strong base capable of accepting a proton and initiating the process, the C104 apparently is not. Actually, one may question to what extent these salts are dissodated in dimethyl formamide. It is possible, therefore, that the reaction involves ion-pairs rather than free ions, and the Li+, Cl- ion-pair may be a more powerful proton acceptor than Li+, CI04-. 

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