Gibbs ring

Plateau Border The region of transition at which thin fluid films are connected to other thin films or mechanical supports such as solid surfaces. For example, in foams Plateau borders form the regions of liquid situated at the junction of liquid lamellae. Sometimes referred to as a Gibbs ring or Gibbs—Plateau Border. 

Fig. 2.5 Plateau border or Gibbs ring (a) at the boundary of a soap film and a rigid wire (b) at the junction of three soap films.

The 1.8 kcal mol 1 less favorable change in Gibbs free energy for the addition of water to [18+] to give [18]-OH in 50/50 (v/v) trifluoroethanol/water (p/CR = -11.3)104 than for addition of water to Me-[6+] in the same solvent (pATR = -12.6)13 shows that the former carbocation is stabilized relative to the alcohol. This stabilization may be the result of the smaller entropic price paid to restrict the / —CH bonds in the five-membered ring at [18+] to conformations that are favorable for hyperconjugation with the cationic carbon. 

Y. Ali, A. C. Richardson, C. F. Gibbs, and L. Hough, Some further ring-opening reactions of methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-epimino-a-D-allopyranoside and its derivatives, Carbohydr. Res., 1 (1968) 255-271. 

The fiavonoidal moiety of ficine was deduced from its UV spectrum, which was very similar to chrysin (37), and the bathochromic shift indicated a saturated alkyl substituent on ring A. Treatment with Gibb s reagent to detect the presence of a proton para to a phenolic OH (17) gave a positive result for 5 but not 4. Although no molecular ion could be seen in the mass spectrum, the peaks obtained were equivalent to the sum of the individual spectra of chrysin (37) and... 

Organic functional groups exert characteristic electronic effects upon other groups to which they are attached. The quantitative expression of such effects can sometimes be correlated by linear Gibbs energy relationships. The best known of these is the Hammett equation, which deals with the transmission of electronic effects across a benzene or other aromatic ring. Consider the acid dissociation constants of three classes of compounds ... 

Now consider the quantitative aspects of heterologous interactions with ring formation. Let Kf be the formation constant and AG° the Gibbs energy change for the reaction of the / end of protomer P with the a end of a second protomer to form the dimer P2 (Eq. 7-25). 

---