S. Mochizuki et al., ACID-BASE INTERACTION FROM THE VIEWPOINT OF MOLECULAR CLUSTERING - EFFECTS OF SOLVENT, PK(A) AND SIZE OF ALKYL GROUP, Journal of the Chemical Society. Faraday transactions, 94(4), 1998, pp. 547-552
Citations number
17
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
Acid-base interactions were investigated by mass spectrometry of clust
ers isolated from solutions containing a carboxylic acid (propionic, b
utyric or hexanoic acid), an aromatic base (pyridine or pyrazine) and
a solvent (water, acetonitrile or propionitrile). In water, self-aggre
gation of the carboxylic acid molecules due to hydrophobic interaction
to form carboxylic acid clusters, such as (butyric acid)(n), was prom
inent, and acid-base interaction proceeded between the carboxylic acid
clusters and the basic molecules. In acetonitrile, the acid-base inte
raction was sensitive to the relative strength of the base. When pyrid
ine (relatively strong base) was used as a base, clustering proceeded
through the formation of a polarized acid-base complex, (acid)(delta-)
(base)(delta+). However, when pyrazine (relatively weak base) was used
as a base, self-aggregation of the acid molecules became favorable. I
n propionitrile, such clusters were not observed because each molecule
was separated by individual solvation. This solvent effect is related
to the solvation structure, which determines the balance between the
self-aggregation of the acid molecules and the formation of the polari
zed acid-base complex. It has also been demonstrated that the balance
of the above intermolecular interactions is also dependent on the size
of the alkyl group of the carboxylic acid. The results of the mass sp
ectrometry partially show the microscopic view for the effect of solve
nt, pK(a) and the size of the alkyl group on the acid-base interaction
in solution.