Formamide 2 molecules

The cyclization of the imine 158 is believed (81UK1252) to involve the addition of the second formamide molecule to C-3 (at least primary amines readily add in a similar manner to such systems). 

A likely pathway is also that in which the key stage is the addition of the second formamide molecule to the carbonyl group of the intermediate 157 to form the amide 159. The latter, with loss of water, closes the dihydropyrimidine ring 160, which undergoes aromatization to 4-metylpyrimidine via 1,4-hydrogen shift and decarbonylation. 

The interaction of two formamide molecules with Li+ has been studied by Rode 213> using a small GTO basis set. He considered two types of geometries in both 1 1 and 1 2 complexes. In the most stable structure of the 1 1 complex the Li+ cation is situated on the CO connection line. In a chelate-like structure the Li+ ion occupies a position which is almost equidistant from the 0 and N atoms. Although this type of 1 2 complex is found to be 70 kcal/mole less stable than the other structure with a linear OLiO arrangement it might be important for larger central ions. 

FIG. 6.4 Molecular volume of the formamide molecule. The heavy line denotes the discrete molecular boundary obtained with Eq. (6.7) and van der Waals radii O, 1.4 N, 1.5 C, 1.7 and H, 1.2 A. The density is a theoretical difference density in the plane of the molecule according to a wave function given by Snyder and Basch (1972). Contours are at 0.05 eA"3 intervals. Negative contours are denoted by short dashed lines and the zero contour by the long dashed line. Source Moss and Coppens (1980). 

Since it has been observed that the hydrogen atoms attached to nitrogen in amines were not easily abstractable in free radical reactions (6, 74), it may be assumed that the aldehydic part of the formamide molecule will be more reactive in the photoaddition reactions than the amino function, thus leading to the following addition reaction with terminal olefins,... 

The simplest model of an amide bond is found in formamide, and several features of protonated formamide are highly relevant to the cleavage of protonated peptides into b and y ions. Amides are bidentate bases, and it has been demonstrated from correlations between core electron energies and proton affinities [213] and from quantum chemical calculations [214] that the carbonyl oxygen is more basic than the amide nitrogen. As demonstrated by FT-ICR, metastable ion dissociation, and RRKM and quantum chemical model calculations [214], the unimolecular dissociation of a protonated formamide molecule depends on which site the proton is attached to ... 

It is worth mentioning that the relative populations of linear and cyclic structures can be shifted by temperature. A recent work which couples experimental measurements with ab initio calculations of quadupole coupling constants determined that rings of six formamide molecules dominate in the liquid state at low temperatures, but are replaced by linear tetramers as T approaches 400° K. 

Only two structural studies have been reported for lithium solvates in non-aqueous solutions. In an XD study of concentrated formamide solution of LiCl [36] the lithium ion was found to be solvated by 5.4 formamide molecules in average and the Li-O distance was reported to be 2.24A, in keeping with the values found in diluted aqueous solutions. More recently, a detailed study has been performed by combination of the ND method with a series of theoretical methods on an 0.6 mol dm LiBr solution in acetonitrile [37]. The lithium ion was found to be tetrahedrally coordinated by three solvent molecules and one bromide ion. The Li-N distance resulted in 2.05 A. 

Critical points in the VSCCs of the respective base and acid atoms. This information enables one to predict positions of attack within a molecule and, hence, the geometries of approach of the reactan For example, a keto oxygen in the formamide molecule has two large non-bonded charge concentrations in the plane of the nuclei (VV = 6.25 and — 6.30 au), while the... 

Flo. 7.10. Displays of — for the formamide molecule in the plane containing the nuclei and in a perpendicular plane containing the C-N axis. The values refer to the non-bonded maxima in the VSCCs of the oxygen and nitrogen atoms. The VSCC of carbon exhibits three bonded maxima in the upper figure. The Laplacian is positive over much of the VSCC of carbon in the plane illustrated in the lower diagram. The two points in this plane where is most positive are the holes in the VSCC of carbon, the points of nucleophilic attack (as indicated by... 

Fig. 5.16 Ball-and-stick diagram of a formamide molecule together with its infrared spectrum as a liquid. (From reference 26, with permission.)...

Fig. 19. (a) Observed 15N chemical shift diagram of poly(L-alanine) in the solid state, (b) Calculated 15N shielding diagram of A-acetyl-r.-alanine methylamide (taking hydrogen bonds with two formamide molecules), as a dipeptide model of poly(L-alanine), by means of the FPT-INDO method. 

Photochemical addition of a formamide molecule onto the double bond of the 3-(/3-D-ribofuranosyl)acrylic ester 76 gave the succinamic ester 77 that cyclized and de-O-protected to a mixture of (/ )- and (5)-dihydroshow-domycin (78) (80MI11) (Scheme 13). 

A formamide intercalation adduct of dickite, Al2Si20s(0H)4, is the first clay-mineral intercalate that has been shown to possess an ordered structiure of interlamellar molecules. Thus, the formamide molecules lie over vacant octahedral sites in the aluminosilicate layers. 

Hydrogen bonding in formamide. The formamide molecule framed in yellow can form hydrogen bonds to three other formamide molecules. 

The chlorine atom is displaced by the nitrogen of a formamide molecule. 

Another formamide molecule reacts wilh the ketone yielding an iV-formylenamide. 

Aminopyrimidines from carboxylic acid amides and 2 formamide molecules... 

This is shown clearly by the Mossbauer spectra of frozen solutions of anhydrous iron(II) chloride in methanol-formamide solvent mixtures of various compositions [Ve 69] each of these spectra consists of the superposition of at least two spectra displaying quadrupole splitting (Fig. 5.5). It may be concluded that the iron in these solutions is present in at least two different solvate sheaths. The spectral part with the smaller quadrupole splitting exhibits values lying close to the AE measured in pure formamide solution (cf.. Table 5.3). Thus, this is probably a line pair originating from a solvate sheath consisting completely or predominantly of formamide molecules. The larger AE can be related to a solvate sheath built up from methanol molecules, for this is close to the AE value obtained in pure methanolic solution. 

An investigation of formamide solutions of potassium iodide [De 68] demonstrated the dependence of the solvation number on the concentration. In dilute solutions, four formamide molecules were coordinated through the oxygen of the carbonyl group to the potassium ion, whereas in concentrated, nearly saturated solutions the number of coordinated formamide molecules was only tv/o. 

In O Fig. 6-1 we show difference maps of the induction energy of the formamide molecule in the field of a unit point charge, computed using the non-local models, local models, and WSM local models, respectively. The large errors in the non-local rank 1 model, particularly near the oxygen and the polar hydrogen atoms, are quite clearly displayed. These errors are reduced in the rank 1 local model and are still smaller in the WSM rank 1 local model. The... 

To investigate the possibilities to decrease the gap values we have investigated a formamide stack (7) (which has similar subunits as the DNA bases) in the same relative position of the units as they are in DNA B (0.336 nm stacking distance and 36° rotation). We have found that the introduction of polarization functions hardly changes the QP band structure of the formamide stack. On the other hand if we have put a phantom formamide molecule at the middle of the stacking distance (0.168 nm), rotated it by 18° and have put a set of 2p functions on each of the 3 non-H atoms, the QP gap decreased... 

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