Die Konformativen Umwandlungen des Ungesättigten Siebenringes in 4.5.6-Trithia-1.2-Benzocycloheptenen-(1) Konformative Beweglichkeit Flexibler Ringsysteme—XVI. Untersuchungen mit Hilfe Der Protonenresonanzspektroskopie

✍ Scribed by K. V. Bredow; A. Jaeschke; H. G. Schmid; H. Friebolin; S. Kabuß

• Publisher: John Wiley and Sons
• Year: 1970
• Tongue: English
• Weight: 757 KB
• Volume: 2
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270020604

✦ Synopsis

The conformational equilibria and conversions of 4.5.6-trithia-l.2-benzocycloheptene-( 1) (1) and the 3'.6 '-dimethoxy-, 3'.6'-dimethyl-and 3'.6'-diphenyl-derivatives (2, 3 and 4) were investigated by NMR spectroscopy. Solutions of these substances are equilibrium mixtures of two conformers, one presumably having a chair form and the other a boat form. The free enthalpy of the boat conformer AGB is dependent on the size of the substituents (R) in the 3' and 6' positions. The AGB values for R = H, OCH,, C6H5 and CH, are 1,03, 0,82, 0,50 and -0,19 kcal/moles, respectively. By slow crystallization one conformer of the substituted trithiabenzocycloheptenes may be obtained in a pure crystalline form. The dimethoxy derivative crystallizes in the chair form, whereas the dimethyl and the diphenyl derivatives crystallize in the boat form. After dissolving the crystals, the conformational equilibrium is restored; at 0°C the half-lifes range from 2 to 15 minutes. By means of the temperature dependence of the NMR