Acid-base properties and gas-phase ion chemistry of (CH/sub 3/)/sub 3/B

Journal Article · Wed Mar 17 00:00:00 EST 1976 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00422a025· OSTI ID:7365394

Murphy, M K; Beauchamp, J L

The ion-molecule reactions of trimethylborane, (CH/sub 3/)/sub 3/B, both alone and in mixtures with other molecules, have been investigated by ion cyclotron resonance spectroscopy. Reaction pathways, product distributions, and reaction rate constants have been determined for a variety of reactions involving both positive and negative ions. Where possible thermochemical data have been obtained, including the gas-phase Broensted acidity, proton affinity, PA((CH/sub 3/)/sub 2/B double bonds CH/sub 2//sup -/) = 365 +- 5 kcal/mole. Attempts to determine the Broensted base strength were frustrated by failure to observe protonated (CH/sub 3/)/sub 3/B. Exothermic proton transfer reactions lead exclusively to the formation of (CH/sub 3/)/sub 2/B/sup +/ and CH/sub 4/. The thermoneutral CH/sub 3//sup -/ transfer reaction (CH/sub 3/)/sub 2//sup 10/B/sup +/ + (CH/sub 3/)/sub 3//sup 11/B reversible (CH/sub 3/)/sub 3//sup 10/B + (CH/sub 3/)/sub 2//sup 11/B/sup +/ is observed to be rapid with k/sub f/ = k/sub r/ = 2.6 x 10/sup -10/ cm/sup 3/ molecule/sup -1/ sec/sup -1/. Transfer of D/sup -/ and F/sup -/ from appropriate reagent anions to (CH/sub 3/)/sub 3/B produces the four-coordinate anions (CH/sub 3/)/sub 3/BD/sup -/ and (CH/sub 3/)/sub 3/BF/sup -/, which are discussed in light of the electron pair acceptor capabilities of the vacant B 2p valence orbital in the neutral. Photoionization efficiency curves for ions generated in (CH/sub 3/)/sub 3/B between 9.7 and 10.8 eV photon energies have been obtained, yielding the adiabatic, ionization potential, IP((CH/sub 3/)/sub 3/B) = 10.01 +- 0.02 eV, the fragmentation threshold, AP((CH/sub 3/)/sub 2/B/sup +/) = 10.35 +- 0.05 eV, and the B--CH/sub 3/ bond dissociation energy in the parent radical ion, D((CH/sub 3/)/sub 2/B/sup +/ - CH/sub 3/) = 7.8 +- 1 kcal/mole. (auth)

• Research Organization: California Inst. of Tech., Pasadena
• OSTI ID: 7365394
• Journal Information: J. Am. Chem. Soc.; (United States), Vol. 98:6
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BORANES
CHEMICAL PROPERTIES
ION CYCLOTRON RESONANCE SPECTROSCOPY
CHEMICAL REACTION KINETICS
DISSOCIATION ENERGY
FRAGMENTATION
GAS ANALYSIS
IONIZATION POTENTIAL
PHOTOIONIZATION
THERMODYNAMIC PROPERTIES
BORON COMPOUNDS
ENERGY
ION SPECTROSCOPY
IONIZATION
KINETICS
PHYSICAL PROPERTIES
REACTION KINETICS
SPECTROSCOPY
400301* - Organic Chemistry- Chemical & Physicochemical Properties- (-1987)
400104 - Spectral Procedures- (-1987)