Proton transfer product predictions

Draw a reasonable proton transfer reaction given the following conditions. 

Answer First decide whether the medium is acidic or basic. With both ethanol and 

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

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The first step is a bimolecular reaction leading to the formation of a hydrogen bond the second step is the breaking of the hydrogen bond such that the protonated species H B+ is formed the third step is the dissociation reaction to form the products. In aqueous solutions, the bimolecular reaction proceeds much faster than would be predicted from gas phase kinetic studies, and this underscores the complexity of proton transfer in solvents with extensive hydrogen-bonding networks capable of creating parallel pathways for the first step. In their au-... 

The modern view of HX addition is that H+ is transferred from HX to the alkene to give a carbocation. The major product is the one derived from the more stable carbocation. Compare the energies of 1-propyl and 2-propyl cations (protonated propene), 2-methyl-1-propyl and 2-methyl-2-propyl cations (protonated 2-methylpropene), and 2-methyl-2-butyl and 3-methyl-2-butyl cations (protonated 2-methyl-2-butene). Identify the more stable cation in each pair. Is the product derived from this cation the same product predicted by Markovnikov s rule Is the more stable carbocation also the one for which the positive charge is more delocalized Compare atomic charges and electrostatic potential maps for one or more pairs of carbocations. 

To predict the direction of reaction, use the balanced equation to identify the proton donors (acids) and proton acceptors (bases), and then use Table 15.1 to identify the stronger acid and the stronger base. When equal concentrations of reactants and products are present, proton transfer always occurs from the stronger acid to the stronger base. 

These results, obtained on a FT-ICR mass spectrometer, led to the proposal that these reactions proceed through long-lived ion-molecule collision complexes which can undergo secondary reactions within the complex. The mechanism, sketched in Scheme 41, predicts the formation of products originating from attack of F on the neutral by proton transfer, SN2 or elimination reactions. 

It has been common practice to equate the value of )3 with the degree of proton transfer in the transition state /3 values close to 0 are taken to be indicative of reactant-like transition states and those close to 1 of product-like transition states. Any value outside these limits is inconsistent with this practice. Early investigators were only able to follow reactions within a limited rate constant range. With the development of fast reaction techniques (Eigen, 1964 Caldin, 1964) the predicted (Br nsted and Pedersen, 1923) curvature of the plots was fully established (cf. Bell and Lidwell, 1940). Pronounced curvature is in fact seen for fast proton transfers in DMSO (see p. 156). 

A new Chapter 3, Proton Transfer and the Principles of Stability, has been added to thoroughly develop how structure determines reactivity using a reaction from general chemistry. Proton transfer mechanisms and product predictions are introduced, setting up the discussion of organic reactions. 

Fig. 9. A typical (unsmoothed with no background substracted) time-of-flight spectrum for the products of the H2+ (v = 5) + H2 reaction at Ecm = 8 eV [15]. The collection time was 20 minutes. The arrows indicate the predicted times for H3+ produced by atom-transfer (AT) and proton-transfer (PT). The other product peaks are labeled in the Figure...

The meaning of at this stage might appear to have little relevance this is not so - the unit value for proton transfer between heteroatoms at A K < 0 indicates that the transition state of the rate-limiting step is close to products as indeed it might be for an endothermic reaction. At ApK>0, = 0 and the transition state would be predicted to be close to reactants in agreement with fact for this exothermic reaction. 

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