Formaldehyde calculation

In a higher level energy calculation, values for the energy computed using the more accurate procedure appear shortly after the Hartree-Fock energy. Here is the output from a formaldehyde calculation done at the MP2 level (RMP2 replaces RHF in the route section ... 

Solution A geometry optimiiation and frequency calculation (both in solution) are needed for each system (we ran the formaldehyde calculations earlier in this chapter). Here are the resulting scaled frequencies associated with carbonyl stretch for each system, along with the corresponding experimental values ... 

Levels of Formaldehyde Calculated from an Internal Coordinate Hamiltonian Using the Lanczos Algorithm. 

Table 7.9 UV spectra (as transition energies in eV) of acetone, acetaldehyde, and formaldehyde, calculated by time-dependent DFT, using Gaussian 98 [78]. The results of using MP2/6-311+G [110] and (calculations by the author) AMI geometries are compared both sets of calculations are single-point B3P86/6-311++G. For each molecule only 6 transitions, all singlets, are shown. The number of positive and negative deviations from experiment and the mean absolute errors are given...

In Table 7 we present the oxygen population in formaldehyde calculated using different methods and at various basis sets. Formaldehyde requires... 

Table 7 Populations in Formaldehyde Calculated Using Various Methods ...

Extensive comparisons have been made of experimental and calculated dipole moments (and in some cases the higher moments, though these are difficult to determine accurately by experiment). Factors such as the basis set and electron correlation can have a significant impact on the accuracy of the results, but it is found in many cases that the errors are systematic and that a simple scaling factor can be used to convert the results of a calculation with a small basis set to those obtained from experiment or with a much larger basis set. To illustrate how calculated dipole moments can vary, Table 2.5 provides the dipole moments for formaldehyde calculated at the experimental geometry using a variety of basis sets. It is... 

TabU 3-5 Dipole moments calculated for formaldehyde using various basis sets at the experimental geometry,... 

Table 5.7 Calculated Values of a and f for Phenol-formaldehyde Resins Formed from Different Proportions of Reactants and Based on Experimental Values of n and n .

Fomialdehyde [50-00-0] H2C=0, is the first of the series of aUphatic aldehydes. It was discovered by Buderov ia 1859 and has been manufactured siace the beginning of the twentieth century. Annual woddwide production capacity now exceeds 15 x 10 t (calculated as 37% solution). Because of its relatively low cost, high purity, and variety of chemical reactions, formaldehyde has become one of the wodd s most important iadustrial and research chemicals (1). 

Example. Calculate the change in Gibbs free energy for the reaction of methanol and oxygen to produce formaldehyde and water at reaction temperatures of 600, 700, 800, 900, and 1,000°K ... 

Urea-formaldehyde moulding powders may be transfer moulded. Pressures of 4-10 ton/in (60-150 MPa), calculated on the area of the transfer pot, are generally recommended. 

Exactly 3 ml. of formaldehyde solution is assayed by the method of U.S.P. XIII, and the result calculated to grams of formaldehyde per milliliter of solution. 

MO (STO-3G) calculations on the gas-phase hydration reaction of formaldehyde suggest a concerted process involving two water molecules as a low-energy mechanism for hydration. 

Typical features of a plywood resole formulation are a formaldehyde-to-phenol molar ratio in the 2.0 1 to 2.5 1 range, programmed formaldehyde, an alkali content from 4 to 8 wt% (calculated as sodium hydroxide), and pan solids of 40-50%. Resins used for laminated veneer lumber (LVL) tend to be similar to plywood resins in composition and molecular weight, though they are often designed for high-end cure speed. 

Fig. 8. Freeman and Lewis-based calculations at a 2 1 formaldehyde-to-phenol molar ratio.

Zavitsas et al. account for the effects of water in their calculations. Water promotes depolymerization of the paraformaldehyde as well as the hemiformals. Their modifications correct for the apparent reduction in methylolation rate as the extent of reaction proceeds, in that the hemiformals remove formaldehyde reactivity from the reaction mixture. Their rate constants look large because they are written for phenate concentrations rather than phenol and because of the formaldehyde equilibrium adjustments. They note that unsalted phenol is a by-... 

These items form the route section, the title section, and the molecule specification section of the input file, respectively. We ll look at each of them again briefly as we set up an input file for an energy calculation on formaldehyde. 

All frequency calculations include thermochemical analysis of the system. By default, this analysis is carried out at 298.15 K and 1 atmosphere of pressure, using the principal isotope for each element type. Here is the start of the ermochemistry output for formaldehyde ... 

Gaussian also includes a facility for estimating molecular volumes for SCRFsDipole calculations. An energy calculation run with the Volume keyword will produce an estimate value for Uq. For example, here is the output indicating the recommended value for Oq for formaldehyde (RHF/6-31+G ) ... 

Next consider the energetics of reduction. Calculate AH for the first step in the reduction process using free reagents (BHT and AlHT). Energies for formaldehyde, and for the two intermediate adducts are provided at left. Which reduction is thermodynamically more favorable Are these results consistent with the predictions made using atomic charges ... 

Interestingly, true hydrides, such as NaH and KH, do not reduce carbonyl groups. Using energies of hydride and methoxide (at left), calculate AH xn for the reduction of formaldehyde by H. Is this reaction more or less favorable than those based on ZH4 Can the low reactivity of NaH and KH be attributed to thermodynamic factors, or must kinetic factors be responsible ... 

DFT molecular dynamics simulations were used to investigate the kinetics of the chemical reactions that occur during the induction phase of acid-catalyzed polymerization of 205 [97JA7218]. These calculations support the experimental finding that the induction phase is characterized by the protolysis of 205 followed by a rapid decomposition into two formaldehyde molecules plus a methylenic carbocation (Scheme 135). For the second phase of the polymerization process, a reaction of the protonated 1,3,5-trioxane 208 with formaldehyde yielding 1,3,5,7-tetroxane 209 is discussed (Scheme 136). 

The transition-state structure of the hetero-Diels-Alder reaction is generally found to be unsymmetrical. Houk et al. have for the reaction of formaldehyde with 1,3-butadiene calculated the C-C and C-0 bond lengths to be 2.133 A and 1.998 A, respectively, in the transition state using ab-initio calculations shown in Fig. 8.12 [25 bj. The reaction of formaldimine follows the same trend for the transition-state structure. 

The hetero-Diels-Alder reaction of formaldehyde with 1,3-butadiene has been investigated with the formaldehyde oxygen atom coordinated to BH3 as a model for a Lewis acid [25 bj. Two transition states were located, one with BH3 exo, and one endo, relative to the diene. The former has the lowest energy and the calculated transition-state structure is much less symmetrical than for the uncatalyzed reaction shown in Fig. 8.12. The C-C bond length is calculated to be 0.42 A longer, while the C-0 bond length is 0.23 A shorter, compared to the uncatalyzed reac-... 

Fig. 8.12 Calculated transition-state structure for the hetero-Diels-Alder reaction of formaldehyde with butadiene [25 bj...

The transition state for the BH3-catalyzed reaction was also found. The favored regioisomer and the influence of the Lewis acid on the reactivity was accounted for by a FMO-way of reasoning using as outlined in Fig. 8.11 to the left. The coordination of BH3 to formaldehyde was calculated to lower the LUMO energy by... 

Food, catabolism of, 1126-1128 Formal charge, 40-41 calculation of, 41-42 summary table of, 42 Formaldehyde, dipole moment of, 39 electrostatic potential map of. 167, 704... 

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