Proton transfer drawing

C21-0030. The reaction between CO2 and H2 O to form carbonic acid (H2 CO3) can be described in two steps formation of a Lewis acid-base adduct followed by Brcjmsted proton transfer. Draw Lewis structures illustrating these two steps, showing electron and proton movement by curved arrows. 

Since the final proton transfer is essential for a successful condensation, it is important to understand what factors drive the proton transfer. Examine the electrostatic potential map of the carbanion, and draw all of the resonance contributors that are needed to describe this ion. How does this ion differ from the others Which product, if either, would be expected from the following condensation Explain. 

Draw the Lewis structure for boric acid, B(OH),. (a) Is resonance important for its description (b) The proton transfer equilibrium for boric acid is given in a footnote to Table 10.1. 

C17-0003. Write the net proton transfer reaction and draw a molecular picture to illustrate the reaction between H3 0+ and SOq. ... 

To draw molecular pictures illustrating a proton transfer process, we must visualize the chemical reactions that occur, see what products result, then draw the resulting solution. When a strong base is added to a weak acid, hydroxide ions remove protons from the molecules of weak acid. When more than one acidic species is present, the stronger acid loses protons preferentially. 

C17-0042. Draw a set of molecular pictures that show the proton transfer reaction occurring when HBr... 

C17-0060. Draw molecular pictures illustrating the proton transfer reactions that determine the pH of the solutions in Problem (b) and (c). 

Much effort has been expanded in drawing mechanistic inferences from the observation that cofacial bismetalloporphyrins containing a non-redox-active metal ion are fairly selective catalysts (e.g., (DPA)CoM, where M = Lu, Sc, Al, Ag, Pd, 2H, i.e., monometallic porphyrins Fig. 18.15). At least two hypotheses have been proposed (i) polarization of the 0-0 bond in catalytic intermediates by the second ion (on an N-H moiety) acting as a Lewis acid [CoUman et al., 1987, 1994] and (ii) spatial positioning of H+ donors especially favorable for proton transfer to the terminal O atoms of coordinated O2 [Ni et al., 1987 Rosenthal and Nocera, 2007]. To the best of my knowledge, neither hypothesis has yet been convincingly proven nor resulted in improved ORR catalysts. When seeking stereoelectronic rational of the observed av values, it is useful to be mindful that a fair number of simple Co porphyrins are also relatively selective ORR catalysts (Section 18.4.2). 

In conclusion, it is apparent that the use of the Br nsted coefficient as a measure of selectivity and hence of transition state structure appears to be based on extensive experimental data. However, the many cases where this use of the Br nsted coefficient is invalid suggest that considerable caution be used in drawing mechanistic conclusions from such data. The limitations on the mechanistic significance of a require further clarification, but the first steps in defining them appear to have been taken. The influence of change in the intrinsic barrier and variable intermolecular interactions in the transition state, both of which will result in a breakdown of the rate-equilibrium relationship, as well as internal return appear to be some of the key parameters which determine the magnitude of the Br nsted coefficient in addition to the degree of proton transfer. 

This reaction is a proton transfer from HC1 to the C=0 group of acetaldehyde. Therefore, it is a Br0nsted-Lowry acid-base reaction, with HC1 acting as the acid (proton donor) and acetaldehyde acting as the base (proton acceptor). Before drawing any curved... 

Problem 2.6 Draw the products of each proton transfer reaction. 

Step [2] Draw the products of proton transfer and identify the conjugate acid and base in the products. 

Problem 2.21 Draw the products of the proton transfer reactions, a. CH3CH2OH + NaH <... 

Step 3 must be fast as it is just a proton transfer between oxygen aU)ms, The decomposition of the etrahedral intermediate is likely to be fast as the leaving group (carbo.xylate ion, piCaH about 5) is jch a good one. The first step, the bimolecular attack of hydroxide on the anhydride, wfill be the atC detennining step. We need only draw the structures of the transition states and we can. onstrua our diagram. 

In principle, the protonation of O- and subsequent deprotonation of C could be condensed into one intramolecular proton transfer step in which the O deprotonates C. However, such a transfer requires a very strained four-membered transition state. It is, therefore, considered poor practice to draw an intramolecular proton transfer, especially when the solvent can serve as a proton shuttle instead. 

Most textbooks do not strongly differentiate polar mechanisms that occur under basic conditions from those that occur under acidic conditions, but the considerations that are brought to bear when drawing polar basic and polar acidic mechanisms are quite different. The typical reagents, the reactive intermediates, and the order of proton transfer steps all differ under acidic conditions from those seen under basic conditions. In this chapter the mechanisms that occur under acidic conditions will be discussed. A lot of time will also be spent discussing carbocations, which are central in these mechanisms. 

Draw a reasonable proton transfer reaction given the following conditions. 

Draw proton transfer with good arrows to a valid Lewis structure and check and charge balance. 

Draw a reasonable proton transfer mechanism for the following reaction catalyzed by sodium hydroxide in heavy water. D stands for deuterium. Treat D2O just like H2O. 

Draw an energy diagram for the proton transfer reaction of CH3COOH + NH3. Calculate the proton transfer to get an approximate AG° for the reaction. 

Draw the proton transfer products for the following reaction and using the p Ta chart in the Appendix, calculate the value of Teq estimate AG° at room temperature. Draw a qualitative energy diagram. 

Draw the proton transfer products and calculate the value of ATeq AG° at room temperature. The cyanoester is not on the chart, but is easily estimated as halfway between the dicyano and the diester. 

Draw the problem space for the following reactant prediction problem. Select the best of two possible substitution alternatives. Hint look at the proton transfer reaction. 

Proton transfer can occur from any acidic to any basic groups or to and from the solvent. A common shortcut in writing mechanisms is to draw just the proton rather than the acid or the protonated solvent, but you should remember that a naked proton will never be floating free in solution. Always check the proton transfer (Section 3.3). 

Draw out every step of the process and look for alternative routes from each step try to find at least one alternative for each step. For hints check resonance forms, proton transfer, alternative sources and sinks, less likely combinations, and higher-energy species. Specifically look for the more obvious decision points covered in this chapter. 

---