Formic acid, model structure

A model study 92) showed that when the hemiacetal (268) was solvolyzed in formic acid, the bicyclic product (269) was isolated in good yield 92). This method was then used to synthesize the tricyclic nucleus of verrucarol (272)92). On reaction with pTsOH, the acetate (270) underwent rapid rearrangement to (271), which constituted part of the structural feature of verrucarol (272) 92K... 

The optimum structure for the first transition state placed the Asp" residue (i.e. our formic acid) reasonably close to the position in which it is found in the enzyme-inhibitor crystal structure [64], However, this functional group is not at all rigid in our model problem. It... 

The separation of synthetic red pigments has been optimized for HPTLC separation. The structures of the pigments are listed in Table 3.1. Separations were carried out on silica HPTLC plates in presaturated chambers. Three initial mobile-phase systems were applied for the optimization A = n-butanol-formic acid (100+1) B = ethyl acetate C = THF-water (9+1). The optimal ratios of mobile phases were 5.0 A, 5.0 B and 9.0 for the prisma model and 5.0 A, 7.2 B and 10.3 C for the simplex model. The parameters of equations describing the linear and nonlinear dependence of the retention on the composition of the mobile phase are compiled in Table 3.2. It was concluded from the results that both the prisma model and the simplex method are suitable for the optimization of the separation of these red pigments. Multivariate regression analysis indicated that the components of the mobile phase interact with each other [79],... 

The carboxyl group occupies a prominent place in protein structure and function and is commonly taken to be ionized as a carboxylate, particularly when paired in a salt bridge with a Whereas this may be the case in a protein environment, it is not obvious that a —COOH group will donate its proton to a base to form an ion pair in the gas phase. For example, SCF calculations with a polarized 6-31G basis set indicate that neither methy-lamine nor an arginine model is able to extract a proton from acetic acid so as to form an ion pair. On the other hand, there is some indication that correlation might stabilize the ion pair for formic acid -f methylamine. ... 

The effects of small changes in the molecular structure can be observed in the case of the related diarylamidines which are the nitrogen analogs of formic acid and which represent models for nucleic acids. In tetrahydrofuran, for N,N -di-(p-F-phenyl)amidine (DFFA) three forms were observed by NMR, a solvated s-cis-form and a solvated s-trans-form which is in fast equilibrium with a cyclic dimer in which a HH-transfer takes place [24] as illustrated in Fig. 6.43. Fortunately, at low temperatures, the s-cis- and the s-trans-forms were in slow exchange. The rate constants of the HH, HD and DD reactions were determined by dynamic H and i F NMR as a function of concentration, deuterium fraction in the mobile proton sites and of temperature. The dependence of the observed rate constants of the s-trans-form on concentration is depicted in Fig. 6.44. The solid lines were calculated using Eq. (6.39) from which the rate constants in the dimer as well as the equilibrium constants of the dimer formation could be obtained. The Arrhenius... 

The disodium salt of 7-nitroso-8-hydroxyquinoline-5-sulphonic acid (Na2L) reacts with Cu " to form CuL,H20. Cu(C10 )2 reacts with 10-methyl-isoalloxazine (L) and aqueous formic acid to form [CuL2](C104)2,4H20, the structure of which is shown as (214). The complex serves as a model compound for metal-flavin enzymes and controverts earlier suggestions that... 

Chemists in the seventeenth century discovered that the substance that gives red ants their irritating bite is an acid with the formula HCHO2. They called this substance formic acid after the ant, whose Latin name is formica rufus. Formic acid has the following structural formula and molecular model ... 

The UNIFAC model and experimental LLE data As it can be seen from Figures 11.2, 11,3, 11.4, and 11.5, the predicted tie lines (dashed lines) are relatively in good agreement with the experimental data (solid lines). In other words, water + formic acid + cumene using universal values for the UNIFAC structural parameters calculated from group contribution data that has been previously reported (Aljimaz et al., 2000 Ghanadzadeh and Ghanadzadeh, 2003 Ince and Ismail Kirbaslar, 2003). 

The formulas of formic acid, H—COOH, acetic acid, CHj—COOH, and propanoic acid, CH3CH2—COOH, suggest the structure of the first three members of a series of carboxylic acids, which contain the carboxyl group, —COOH. Their Lewis diagrams and ball-and-stick models are shown in Figure 13.19. As with hydrocarbons, alcohols, and ethers, the carbon chain may extend indefinitely. 

The tendency of a transition metal hydride to transfer H to a substrate is called hydricity [ 12]. It is possible to determine the Gibbs free energy of the splitting of the covalent polar M-H bond to afford a metal cation and the hydride ion in solution. The hydricity is not parallel to the polarity of the M-H IxMid, nor can it be predicted on the basis of the electronic structure of the metal atom. It is a complex property that can be modeled for transition metal hydrides using multiparameter approaches. The hydricity concept applies to the interaction of M-H bonds with CO2 as well [13]. The reactivity of M-H bonds toward CO2 is linked to reactions that may have industrial interest, such as the hydrogenation of CO2 to afford formic acid (4.2) and the electrochemical reduction of CO2 to other Cl or C1+ molecules (4.3). 

In research involving cocrystals of the model pharmaceutical compound caffeine (29a) was prepared via solid-state grinding (a Retsch MM200 mixer mill was used) and solution crystallization, it was demonstrated that these two methods of preparation are not always equivalent with respect to the cocrystal product obtained. Reported in this work are the structures of five previously unreported caffeine cocrystals with monocarboxylic acids, including formic acid, acetic acid, and trifluoroacetic acid (05CGD2233). The structures were determined by powder and single crystal X-ray diffraction. 

---