A Computational Study of the Role of Hydrogen Bonds in SN1 and E1 Reactions

Journal of Computational Chemistry

Volumn 25, Issue 4, 2004, Pages 598-608

  Yamabe, Shinichi ^a   Tsuchida, Noriko ^a  

^a NARA UNIVERSITY OF EDUCATION   (Japan)

Author keywords

Hydrogen bonds; Proton relay; SN1 and E1 reactions; Transition states

Indexed keywords

HALIDE MINERALS; MOLECULAR STRUCTURE; PROBABILITY DENSITY FUNCTION; QUENCHING; SOLVENTS; STEREOCHEMISTRY; THERMAL EFFECTS; WATER;

HETEROLYSIS; PROTON RELAY; SN1 AND E1 REACTIONS; TRANSITION STATES;

HYDROGEN BONDS;

EID: 84962438999     PISSN: 01928651     EISSN: None     Source Type: Journal    
DOI: 10.1002/jcc.10412     Document Type: Article

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24. T (residual moiety after a water trimer is removed). Δe for the subtraction of the trimer of black-color water molecules is -53.86 kcal/mol. This very large value indicates that the trimer is strongly bound to the residual part. This value is larger than that for subtraction of another water trimer. For instance, Δe for subtraction of a cyclic trimer, which is composed of two black-color water molecules and H37-036-H38, is -40.31 kcal/ mol. The subtraction way is also explained in Figure S6 (Supporting Information).
25. N1:E1 product ratio 95%:5%, has been stated. The ratio corresponds to an energy difference, 1.76 kcal/mol, according to the Boltzmann's factor (T = 300 K). The energy is fortuitously the same as the difference between ΔE = -7.28 kcal/mol (Int2) and ΔE = -5.52 kcal/mol (E1 product). However, by RB3LYP/6-311+G(2d,p) SCRF = PCM, the difference between [ΔE = -8.10 kcal/mol (Int1)] and [ΔE = -3.34 kcal/mol (El product)] becomes larger.
26. -. ΔE values of Int2 and E1 product are not so different between SCRF = dipole and SCRF = PCM, because the two ions are near with each other. The ΔE values are, thus, affected by SCRF methods, but our discussions are insensitive to them.
27. Entropies of Reactant and, intermediates and El product in Figure 6 were obtained by RB3LYP/6-31G* SCRF = dipole vibrational analyses. They are 210.0 e.u. (Reactant), 191.8 e.u. (Int1), 192.2 e.u. (Int2), and 204.6 e.u. (El product) at T = 300 K and P = 1 atm, respectively. Among the four values, that of Reactant is largest, which arises obviously from the flexible hydrogen-bond structure around the organic molecule, t-Bu-Cl. Those of Int1 and Int2 are smaller (∼ 192 e.u.), which means that water clusters are constrained by the closed circuit containing the charged species. That of El product is larger (=204.6 e.u.), which means that the iso-butene moiety is liberated from the circuit. Thus, from the standpoint of entropies, "Int1" and "Int2" are intermediates where the t-Bu moiety is not liberated yet.