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Theoretical studies on the gas‐phase smiles rearrangement
Author(s) -
Kim Chang Kon,
Lee Ikchoon,
Lee BonSu
Publication year - 1991
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610040509
Subject(s) - chemistry , steric effects , smiles rearrangement , enthalpy , reactivity (psychology) , gas phase , ring (chemistry) , stereochemistry , thermodynamics , organic chemistry , medicine , physics , alternative medicine , pathology
Gas‐phase Smiles rearrangements and S N i processes of ions C 6 H 5 X(CH 2 ) n Y − (X, Y = 0 or S, and n = 2–4) have been studied by the AM1 MO method. The Smiles rearrangement to an ortho position of the phenyl ring is diffcult owing to involvement of a high‐energy barrier process involving a 1,2‐hydrogen shift. The reactivity of the Smiles rearrangement to the ipso position increases in the order X O and Y S < X S and Y O < X Y 0 as a result of steric and electronic effects in the transition state (TS). The reactivity order with respect to the side‐chain length, n = 3 < 4 < 2, is mainly determined by ring strain in the TS. For the S N i process, in which Y attacks the β‐carbon (β to phenyl), the enthalpy (δ H ≠ ) factor becomes more favourable but the entropy (δ S ≠ ) factor becomes unfavourable with an increase in the side‐chain length, in agreement with a general trend for cyclization processes. The product ratio in the Smiles rearrangement and the S N i process is largely controlled by the thermodynamic stabilities of the products, as observed in gas‐phase experiments.