Acetaldehyde calculation

Scheme 9.31 Cyclic transition states for the (M)-l, 2-butadienylzinc additions to acetaldehyde calculated at the B3LYP/6-31G level of theory.

Assume that the reaction rates are both first-order in ethanol and that no products are initially present. After 100 s in a constant volume system, there is 30 percent of the ethanol remaining and the mixture contains 13.7 percent ethylene and 27.4 percent acetaldehyde. Calculate the rate constants and 2-Compound A is converted to B in a CSTR. The reaction rate is first-order with a reaction rate constant of 20 min. Compound A enters the reactor at a flow rate of 12 m /min (concentration of 2.0 kmol/m ). The value of the product B is 1.50 per kmol and the cost of reactor operation is 2.50 per minute per cubic meter. It is not economical to separate unconverted A to recycle it back to the feed. Find the maximum profit. 

Table 4 The TDHF Transition Dipole Moments (in Debye) for the l A Transition (n n excited state) in Acetaldehyde Calculated with Dunning s Correlation Consistent cc-VXZ Basis Sets" PA"...

Detailed analyses of the above experiments suggest that the apparent steps in k E) may not arise from quantized transition state energy levels [110.111]. Transition state models used to interpret the ketene and acetaldehyde dissociation experiments are not consistent with the results of high-level ab initio calculations [110.111]. The steps observed for NO2 dissociation may originate from the opening of electronically excited dissociation chaimels [107.108]. It is also of interest that RRKM-like steps in k E) are not found from detailed quantum dynamical calculations of unimolecular dissociation [91.101.102.112]. More studies are needed of unimolecular reactions near tln-eshold to detennine whether tiiere are actual quantized transition states and steps in k E) and, if not, what is the origin of the apparent steps in the above measurements of k E). 

Ab initio MO calculations using 4-3IG orbitals indicate that the eclipsed conformation of acetaldehyde is more stable than the staggered conformation. 

Figures 17A and 17B (p. 183) show energy as a function of rotation for a series of 1-substituted acetaldehydes, with 6 = 0° in the syn conformation and 6 = 180° in the anti conformation. The calculations were done using the PM3 method. Figure 17A for a vacuum, whereas Fig. 17B is for a solvent cavity with a dielectric constant of 4." The table gives the calculated barriers. Discuss the following aspects (a) rationalize the order Br > Cl > F for syn conformers (b) rationalize the shift to favor the am. conformation in the more polar environment. 

Once the order of the reaction is known, the rate constant is readily calculated. Consider, for example, the decomposition of acetaldehyde, where we have shown that the rate expression is... 

Having established the value of k and the reaction order, the rate is readily calculated at any concentration. Again, using the decomposition of acetaldehyde as an example, we have established that... 

Apparent activation energies for the catalytic reactions were as expected about 80 kJ/mol for the formation of formaldehyde and 60 kJ/mol for the formation of acetaldehyde from the respective alcohols (Figure 3). The turnover rates of the samples were calculated either on the basis of the number of vanadiums (all of which could be assumed to be accessible) or by assuming that oxygen uptake counted the catalytic sites ... 

Figure 3. Arrhenius plots for the formation of formaldehyde or acetaldehyde from methanol or ethanol, normalized by the number of vanadiums (open symbols) and by the amount of oxygen uptake measured at 625 K (filled symbols). Lines on the right panel are calculated from the data reported by Oyama and Somorjai [11].

Detailed structural calculations have been carried out for this system. This is because the neutral isomer, C2HsO, which is implicated in the thermochemistry of ethanol, is of interest in pollution control, atmospheric chemistry, and combustion. Also, there is new information available from photoionization experiments with which to compare theoretical calculations. For details of these comparisons, see Curtiss et al.73 In the earlier theoretical studies of Nobes et al.,74 calculations were performed at the MP2 and MP3 levels with basis sets of double plus polarization (6-13G ) with electron correlation. These studies revealed four stable minima for the system protonated acetaldehyde, CHj-C H-OH <-> CH3-CH=0+H the methoxymethyl cation, CH3OCH2 protonated oxirane, (CH2)2OH+ and vinylox-... 

It is well known that the catalytic effect of Ti02 is attributed to the generation of a strong oxidant, hydroxyl radicals [44]. Following this theory, the quantum efficiency of the felt material prepared with the titania/silica fiber was calculated from the aforementioned result. In this case, if the number of molecules is significantly larger than the number of photon, acetaldehyde is oxidized to CH3COOH as follows ... 

Carbonyl group of the aldehyde decreases the BDE of the adjacent C—H bond. This is due to the stabilization of the formed acyl radical, resulting from the interaction of the formed free valence with Tr-electrons of the carbonyl group. For example, DC—H = 422kJmol 1 in ethane and D( n 373.8 kJ mol 1 in acetaldehyde. The values of Dc H in aldehydes of different structures are presented in Table 8.1. In addition, the values of the enthalpies of acylperoxyl radical reactions with aldehydes were calculated (D0 H= 387.1 kJ mol-1 in RC(0)00 H). 

Finally, Nagaoka et al have made a very interesting study applying MC-FEP techniques to the vinyl alcohol - acetaldehyde tautomerism.32 Using a cluster of the solute with three water molecules as a solute , the free energy for the tautomerism was calculated along different reaction pathways, which had been previously found by ab initio calculations including an SCRF solvation term. They were able to deduce that a two-step mechanism is favoured over a concerted one for the transfer of the proton. 

Acetaldehyde (A) decomposes according to the reaction, CH3CH0 = CH4 + CO. Two sets of experiments were performed by Letort (Bull Soc Chim France 9 1, 1942) and the tabulated calculations were derived from them, (a) With a pressure of 183 torr, the data are of composition na/na0 and the corresponding rates (b) At several initial pressures the initial rates are given. Find the order of the reaction from the two sets of data. 

Figure 2.25 Vapour pressures of acetaldehyde, water, dioxane, ethylene glycol and diethylene glycol, where the data have been calculated from the database of the commercial process simulator Chemcad (Chemstations)...

Calculations support a cooperative mechanism for the hydration of formaldehyde, acetaldehyde, acetone, and cyclohexanone in water. The results are supported by determination of the rate constant for the neutral hydration of acetone, using labelled acetone and water. Conclusions include ... 

Chemical/Physical. Atkinson et al. (2000) studied the kinetic and products of the gas-phase reaction of 2-heptanone with OH radicals in purified air at 25 °C and 740 mmHg. A relative rate constant of 1.17 x 10 " cmVmolecule Sec was calculated for this reaction. Reaction products identified by GO, FTIR, and atmospheric pressure ionization tandem mass spectroscopy were (with respective molar yields) formaldehyde, 0.38 acetaldehyde, L0.05 propanal, X0.05 butanal, 0.07 pentanal, 0.09 and molecular weight 175 organic nitrates. 

The excellent agreement with the experimental and calculated isotope effect (calculated for formaldehyde, 3.22, and for acetaldehyde, 3.3 experimental value 2.9) supports the computational approach. This suggests that the computed transition structure for hydride transfer in the reaction of the lithium enolate of acetone with acetaldehyde (Figure 30) is realistic. 

FIGURE 29. Optimized geometries for the reactants, transition structures and products in the sequence of reactions between the hthium enolate (LiEn) derived from acetaldehyde and formaldehyde. The total reaction sequence is LiEn- -CH20->complex-l- TSl->-Pl->-complex-2->-TS2->-P2 (Figure 28)->-TS3 (Figure 30)->-P3 (Figure 28). Theoretical calculations were carried out at the HF/6-31H—l-G level. Reprinted with permission from Reference 29. Copyright 1998 American Chemical Society... 

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