Dynamics of a conformational change in aqueous 18-crown-6 by an ultrasonic absorption method
✍ Scribed by Gerard W. Liesegang; Michael M. Farrow; Licesio J. Rodriguez; Roger K. Burnham; Edward M. Eyring; Neil Purdie
- Publisher
- John Wiley and Sons
- Year
- 1978
- Tongue
- English
- Weight
- 595 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0538-8066
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✦ Synopsis
A temperature dependence study of the ultrasonic amplitudes, velocities, and relaxation times for a presumed conformational transition of noncomplexed aqueous 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) is discussed. At all temperatures a single relaxation was observed within a 15-255-MHz frequency range. The equilibrium constant for the presumed conformational transition CRI FCRz was determined to be Kzl = (2 f 2) X
The activation parameters are AHzl# = 10.2 f 1.0 kcal/mol, ASX# = 7.7 f 0.2 cal/(mol-deg), AHlz# = 7.4 f 1.0 kcal/mol, and ASlzf = 7.7 f 0.2 cal/(mol-deg), while the thermodynamic enthalpy and entropy were found to be -2.6 f 1.0 kcal/mol and 0 f 0.2 cal/(mol-deg), respectively. The rate constants a t 25.0"C for the presumed conformational transition are kz1 = (1.0 f 0.3) X lo7 sec-I and k I 2 = (6.2 0.2) X lo8 sec-'.