Showing papers in "Journal of the American Chemical Society in 1966"

Silylations with Bis(trimethylsilyl)acetamide, a Highly Reactive Silyl Donor

Abstract: Silyl-proton exchange reactions with bis(trimethylsilyl)acetamide proceed rapidly and quantitatively under mild conditions. The preparative silylation of amides, ureas, and amino acids, as well as hindered phenols, carboxylic acids, and enols, is described. Examples of silylation as a protective measure and a means of preparing reactive intermediates are included.

The Dimerization of Chlorophyll a, Chlorophyll b, and Bacteriochlorophyll in Solution1

Abstract: ~ . · . Analyses· of the absorption spectra of three chlorophylls in carbon tetrach1oride solution demonstrate the existence of monomerdimer equilibrium in the concentration range from 10-6 to 10-3 mole-1-1• ' . 2 J~ ' 1 Tne dimerization constants, Kd = Cd/Cm, are (1~0~ 0.4).x 10 1-mole~ . for ·chlorophyll ~'. (0.~ + 0.3) x 104 1-mole-1 for chiorophyll .Q. and '; (2.2 + 0. 7) x 10~. 1-mole-1 for bacteriochlorophyll at 24 + 2°C, ·. . correspondU\~ to standard free energies of dimer formation of -5.4, ' . . -5.3 and -5.8 kcal-mole-1, respectively. The ·absorption spectra of pure monaner and pure dimer in carbon tetrachloride are calculated for each.pigment. For each of the'chlorophyll dimers the· long wavelength absorption band consists of a principal ·;. :, peak centered at .ap~roximately the position of the monomer absorption maximun an~ a s~ulder ·to long wavelengths. The relative 'oscillator : strengths of th~ split components indicate that the corresponding ., . transition;m~ts for the two molecules in each d:1mer are. neari.y I . l ' ' .. ;