Measurement by NMR spectrometry of hydrogen bonding to bases having more than one equivalent electron donor site
✍ Scribed by Kim F. Wong; Teck S. Pang; Soon Ng
- Publisher
- Elsevier Science
- Year
- 1975
- Tongue
- English
- Weight
- 535 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0009-2614
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✦ Synopsis
The hydrogen bonding psmmeters for the interaction of chloroform with several Lewis bases having one or t%'o eqtivalent electron donor sites are obtained on the basis of the formation of a simpie 1:l complex. The twin-site bas,eshavesimilar structure and are considered to have ncariy the same site strength and about the same steric requirements as the corresponding single-site bases. Shere nre large differences in the equilibrium constant K and the change in enthdpy between the single-site and the corresponding twin-site bases. In the twinsite base the number of donor sites exceeds the number of molecules, and the observed chloroform proton shift is much larger than that in the sin&-site base of the s=me concentration. An important question therefore concerns the significance of the K obtained by using the acttrzl concentration Cm terms of molecules) in the case of the twin-site base. Relative to the single-site bases the temperature dependence ofK is enhanced in the open chain txvin-site bases, whereas the opposite is found in the cyclic twin-site basses. The reasons For such a