The acid-catalyzed transacetalation of cyclophane formaldehyde acetals incorporating m-xylylene units (m-Ci) generates a well behaved dynamic library of oligomeric macrocycles. Effective Molarities (EM) relating to the formation of the lower cyclic oligomers (i = 2-4) were estimated from equilibrium concentrations measured under conditions closely approaching the critical monomer concentration. Comparison with available EM data relating to the formation of the isomeric paracyclophanes p-C-i shows that the metacyclophanes m-Ci are considerably more stable, the stability difference being particularly significant for i = 2. Molecular modeling indicated that incorporation of COCOC moieties in the cyclic structures enforces deviations from the most stable g(+)g(+)/g(-)g(-) conformation. Consistently with experimental results, such deviations are at a maximum for the dimeric paracyclophane p-C-2, and tend to decrease with increasing ring size in both series, Molecular modeling also showed that the stability of the heterodimer m,p-C-2 is comparable to that of m-C-2, which is again in agreement with the results of a cross-experiment in which a mixture of m-C-2 and p-C-2 was allowed to equilibrate.

Metathesis reactions of formaldehyde acetals - Experimental and computational investigation of isomeric families of cyclophanes under dynamic conditions / Cacciapaglia, R; DI STEFANO, Stefano; Mandolini, Luigi; Mencarelli, Paolo; Ugozzoli, F.. - In: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY. - ISSN 1434-193X. - (2008), pp. 186-195. [10.1002/ejoc.200700906]

Metathesis reactions of formaldehyde acetals - Experimental and computational investigation of isomeric families of cyclophanes under dynamic conditions

DI STEFANO, Stefano;MANDOLINI, Luigi;MENCARELLI, Paolo;
2008

Abstract

The acid-catalyzed transacetalation of cyclophane formaldehyde acetals incorporating m-xylylene units (m-Ci) generates a well behaved dynamic library of oligomeric macrocycles. Effective Molarities (EM) relating to the formation of the lower cyclic oligomers (i = 2-4) were estimated from equilibrium concentrations measured under conditions closely approaching the critical monomer concentration. Comparison with available EM data relating to the formation of the isomeric paracyclophanes p-C-i shows that the metacyclophanes m-Ci are considerably more stable, the stability difference being particularly significant for i = 2. Molecular modeling indicated that incorporation of COCOC moieties in the cyclic structures enforces deviations from the most stable g(+)g(+)/g(-)g(-) conformation. Consistently with experimental results, such deviations are at a maximum for the dimeric paracyclophane p-C-2, and tend to decrease with increasing ring size in both series, Molecular modeling also showed that the stability of the heterodimer m,p-C-2 is comparable to that of m-C-2, which is again in agreement with the results of a cross-experiment in which a mixture of m-C-2 and p-C-2 was allowed to equilibrate.
2008
cyclooligomerization, dynamic covalent chemistry, effective molarity, molecular modeling, transacetalation
01 Pubblicazione su rivista::01a Articolo in rivista
Metathesis reactions of formaldehyde acetals - Experimental and computational investigation of isomeric families of cyclophanes under dynamic conditions / Cacciapaglia, R; DI STEFANO, Stefano; Mandolini, Luigi; Mencarelli, Paolo; Ugozzoli, F.. - In: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY. - ISSN 1434-193X. - (2008), pp. 186-195. [10.1002/ejoc.200700906]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/226490
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