ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Gas-phase Smiles rearrangements and SNi processes of ions C6H5X(CH2)nY- (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 SNi process, in which Y attacks the β-carbon (β to phenyl), the enthalpy (δH≠) factor becomes more favourable but the entropy (δS≠) 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 SNi process is largely controlled by the thermodynamic stabilities of the products, as observed in gas-phase experiments.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610040509
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