Comparative stabilities of cationic and anionic hydrogen-bonded networks. Mixed clusters of water-methanol

Journal Article · Wed Oct 01 04:00:00 EDT 1986 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00280a014· OSTI ID:5058366

Meot-Ner, M ^[1]

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1. Mautner

The thermochemistry of the mixed water-methanol cationic clusters (H/sub 2/O)/sub n/(CH/sub 3/OH)/sub m/H/sup +/ and anionic clusters ((H/sub 2/O)/sub n/(CH/sub 3/OH)/sub m/ - H)/sup -/ (i.e. clusters containing OH/sup -/ or CH/sub 3/O/sup -/) was measured. The stability of the total hydrogen-bonded network in each positive cluster is greater by 3-6 kcal/mol than in the corresponding negative cluster. The variation of the stabilities of the cationic and anionic clusters with composition shows remarkable similarities. (1) Both H/sub 3/O/sup +/ x nH/sub 2/O and OH/sup -/ x nH/sub 2/O show effects of solvent shell filling at n = 3. (2) Both for anions and cations, neat methanol clusters are more stable than neat water clusters. (3) Both CH/sub 3/OH/sub 2//sup +/ and CH/sub 3/O/sup -/ are solvated more strongly by methanol than by water. (4) Stepwise ion solvation compresses the differences between the gas-phase acidities of H/sub 2/O and CH/sub 3/OH and also between the gas-phase basicities. The compression effect with increasing solvation is somewhat larger in the positive than in the negative ions. (5) Both for anions and cations, stepwise replacement of H/sub 2/O by CH/sub 3/OH is exoergic for every step from neat water methanol. The results indicate that in the water-methanol clusters, the favored topology places methanol molecules near the charged centers and water molecules at the periphery. This is in contrast to blocked clusters such as water-acetonitrile, where hydrogen-bonding requirements place water at the protonated center and acetonitrile at the periphery.

• Research Organization: National Bureau of Standards, Gaithersburg, MD
• OSTI ID: 5058366
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 108:20; ISSN JACSA
• Country of Publication: United States
• Language: English

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ADDUCTS
ALCOHOLS
ANIONS
CATIONS
CHARGED PARTICLES
CHEMICAL BONDS
DATA
ELEMENTS
EXPERIMENTAL DATA
HYDROGEN
HYDROGEN COMPOUNDS
HYDROXY COMPOUNDS
INFORMATION
IONS
METHANOL
NONMETALS
NUMERICAL DATA
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
PH VALUE
PHYSICAL PROPERTIES
SOLVATION
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
WATER