Handbook of Solvents - George Wypych - ChemTech - Ventech!

30 Estanislao Silla, Arturo Arnau and Iñaki Tuñón
Figure 2.1.12. Models of the reaction studied for the addition of azide anion to tetrafuranosides. The experimental
product ratio is also given.
The influence of the solvent on the rate at which a chemical reaction takes place was
already made clear, in the final stages of the XIX century, with the reaction of Menschutkin
between tertiary amines and primary haloalkanes to obtain quaternary ammonium salts. 64
The reaction of Menschutkin between triethylamine and iodoethane carried out in different
media shows this effect (Table 2.1.3):
2.1.4.3 Example of application: addition of azide anion to tetrafuranosides
The capacity of the solvent to modify both the thermodynamic and also the kinetic aspects
of a chemical reaction are observed in a transparent manner on studying the stationary structures
of the addition of azide anion to tetrafuranosides, particularly: methyl
2,3-dideoxy-2,3-epimino-α-L-erythrofuranoside (I), methyl 2,3-anhydro-α-L-erythrofuranoside
(II), and 2,3-anhydro-β-L-erythrofuranoside (III). An analysis with molecular
orbital methods at the HF/3-21G level permits the potential energy surface in vacuo to be
characterized, to locate the stationary points and the possible reaction pathways. 65 The effect
of the solvent can be implemented with the aid of a polarizable continuum model. Figure
2.1.12 shows the three tetrafuranosides and the respective products obtained when azide
anion attacks in C3 (P1) or in C4 (P2).
The first aim of a theoretical study of a chemical reaction is to determine the reaction
mechanism that corresponds to the minimum energy path that connects the minima of reactant
and products and passes through the transition state (TS) structures on the potential en-