Electrospray ionization of tyrosine from a 3:1 (v:v) CH3OH/H2O solution is found to afford an M − H ion which 70:30 mixture phenoxide and carboxylate ions. This corresponds the gas-phase equilibrium composition not liquid-phase proportions. In contrast, produced as dominant (∼95%) anhydrous CH3CN CH3CN/H2O mixtures. The addition small amounts CH3OH solvent, however, convert back into isomeric ratio. structure therefore depends on solvent system sprayed.

Preferred protonation: Does electrospray ionization mass spectrometry produce gas-phase or liquid-phase structures? The preferred protonation site in p-aminobenzoic acid depends upon the medium, and structure of its conjugate varies with solvent used during spraying.

Infrared multiphoton dissociation spectra of protonated p-aminobenzoic acid generated by electrospray ionization (ESI) from aqueous methanol and acetonitrile solutions were recorded in the gas phase 2800-4000 cm(-1). The O-protonated ion is more stable than N-protonated structure phase, whereas opposite true both solutions. When CH(3)OH/H(2)O was used as ESI solvent, only observed. In contrast, a 70:30 mixture O- species produced CH(3)CN/H(2)O. These structural assignments are based on an...

The pK(a) of an acyclic aliphatic heptaol ((HOCH(2)CH(2)CH(OH)CH(2))(3)COH) was measured in DMSO, and its gas-phase acidity is reported as well. This tertiary alcohol found to be 10(21) times more acidic than tert-butyl DMSO order magnitude acetic acid (i.e., = 11.4 vs 12.3). can attributed a 21.9 kcal mol(-1) stabilization the charged oxygen center conjugate base by three hydrogen bonds another 6.3 resulting from additional between uncharged primary secondary hydroxyl groups. Charge...

Proton affinities for a diverse set of 35 anions were calculated using 7 different levels density functional theory (S-null, S-VWN, S-LYP, B-null, B-VWN, B-LYP, and Becke3-PW91). These combinations functionals cover the range those that are widely available. The basis-set dependence these methods was explored split-valence, double- vs triple-zeta, correlation- noncorrelation-consistent bases (6-31+G(d), 6-311++G(2df,2pd) aug-cc-pVDZ aug-cc-pVTZ). results compared to modest high-level ab...

Both C−H bond dissociation energies for cyclobutene were measured in the gas phase (BDE = 91.2 ± 2.3 (allyl) and 112.5 2.5 (vinyl) kcal mol-1) via a thermodynamic cycle by carrying out proton affinity electron-binding energy measurements on 1- 3-cyclobutenyl anions. The results compared to those an acyclic model compound, cis-2-butene, provide needed information experimentally establish heat of formation cyclobutadiene. Chemically accurate G3 W1 calculations also carried cycloalkanes,...

Hydrogen−deuterium exchange experiments were carried out on the conjugate base of cysteine with four different deuterated alcohols. Three H/D exchanges are observed to take place in each case, and a relay mechanism which requires SH CO2H groups have similar acidities subsequently proceeds through zwitterionic intermediate is proposed. Gas-phase acidity measurements also quadrupole ion trap using extended kinetic method Fourier transform mass spectrometer by an equilibrium determination. The...

Hydrogen bonds are the dominant motif for organizing three-dimensional structures of biomolecules such as carbohydrates, nucleic acids, and proteins, serve templates proton transfer reactions. Computations, gas-phase acidity measurements, pK(a) determinations in dimethyl sulfoxide on a series polyols indicate that multiple hydrogen to single charged center lead greatly enhanced acidities. A new class Brønsted consequently, is proposed.

Hydrogen bond interactions in small covalent model compounds (i.e., deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH(2)CH(2))(2)CHO(-)(2a), (HOCH(2)CH(2))(3)CO(-) (3a), (HOCH(2)CH(2)CH(OH)CH(2))(3)CO(-) (4a)reveal that hydrogen-bonded networks can provide enormous stabilizations a single charge center not only be stabilized up to three hydrogen bonds but...

Electron-withdrawing trifluoromethyl groups were characterized in combination with hydrogen-bond interactions three polyols (i.e., CF3CH(OH)CH2CH(OH)CF3, 1; (CF3)2C(OH)C(OH)(CF3)2, 2; ((CF3)2C(OH)CH2)2CHOH, 3) by pKa measurements DMSO and H2O, negative ion photoelectron spectroscopy binding constant determinations Cl(-). Their catalytic behavior several reactions also examined compared to a Brønsted acid (HOAc) commonly employed thiourea ((3,5-(CF3)2C6H3NH)2CS). The of inductive...

A new class of readily prepared thiourea catalysts with one or more positively charged centers and no hydrogen-bonding sites are exploited in several bond-forming reactions orders magnitude reactive than Schreiner's thiourea. These findings provide the basis for a strategy activating hydrogen-bond catalysts.

Cycloadditions of epoxides with CO2 to synthesize cyclic five-membered ring organic carbonates are broad interest from a synthetic, environmental, and green chemistry perspective, the development effective catalysts for these transformations is an ongoing challenge. A series eight charge-containing thiourea salts that catalyze reactions under mild conditions (i.e., 60 °C atmospheric pressure) reported. Substrate scope mechanistic studies were also carried out, isotope effects measured,...

Clusters of oxalate and malonate dianions with glycine in its zwitterionic form were found by ab initio density functional theory calculations. Proton transfer is impeded an electrostatic barrier, but the resulting anion−anion pairs complexes despite having negative dissociation energies. A variety X-/Y- species exothermic energies ranging from 10 to 141 kcal mol-1, large enough barriers be experimentally produced, are reported. These may represent unrecognized control element nature provide...

Density functional theory was used to examine the solvation number and aggregation state of several alkyllithium compounds in clusters with tetrahydrofuran molecules coordinated each lithium atom. We then made microsolvation approximation approximated bulk free energy by clustering solvent gas phase. The trends computed results are reasonable agreement available experimental data.

Radical anions of o-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation differentiated. Classical derivatization experiments also carried out to authenticate the ortho meta anions. Gas-phase techniques used measure proton affinities all three radical o- m-benzoquinone. By combining these results thermodynamic cycles, we derived heats hydrogenation (ΔhydH°(1o, 1m, 1p) = 42.8 ± 4.1, 74.8 38.5 3.0...

Deprotonation of tyrosine in the gas phase was found to occur preferentially at phenolic site, and conjugate base consists a 70:30 mixture phenoxide carboxylate anions equilibrium. This result established by developing chemical probe for differentiating these two isomers, presence both ions confirmed photoelectron spectroscopy. Equilibrium acidity measurements on indicated that ΔGacid° = 332.5 ± 1.5 kcal mol−1 ΔHacid° 340.7 mol−1. Photoelectron spectra yielded adiabatic electron detachment...

Enzymes and their mimics use hydrogen bonds to catalyze chemical transformations. Small-molecule transition state analogues of oxyanion holes have been characterized by computations, gas-phase IR photoelectron spectroscopy, determination binding constants in acetonitrile. A new class bond catalysts is proposed (donors that can contribute three a single functional group) demonstrated Friedel-Crafts reaction. The employed catalyst was observed react 100 times faster than its rotamer employ...

We report quantifying the strengths of different types hydrogen bonds in hydrogen-bond networks (HBNs) via measurement adiabatic electron detachment energy conjugate base a small covalent polyol model compound (i.e., (HOCH2CH2CH(OH)CH2)2CHOH) gas phase and pKa corresponding acid DMSO. The latter result reveals that to charged center those are one solvation shell further away primary secondary) provide 5.3 2.5 units stabilization per bond Computations indicate these energies increase 8.4 3.9...

Acidities are commonly measured in polar solvents but catalytic reactions typically carried out nonpolar media. IR spectra of a series phenols CCl4 and 1% CD3CN/CCl4 provide relative acidities. Nonprotonated charged substituents with an appropriate counterion found to enhance their Brønsted acidities improve catalyst performance by orders magnitude.

We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and diazomethyl radical: EA(Χ 3Σ- CNN) = 1.771 ± 0.010 eV, 2A'' HCNN) 1.685 0.006 DCNN) 1.678 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: 1.83 0.03 1.69 make use CNN HCNN, together with gas phase acidity diazomethane, ΔacidH298(HCHN2) 372.2 2.1 kcal mol-1 (CBS calculated value 373.4 0.7), find bond...

How unstable can it be? Gas-phase measurements on the 3-cyclobutenyl cation were combined in a thermodynamic cycle to provide first experimental determination of heat formation cyclobutadiene (see scheme, IP=ionization potential, BDE=bond-dissociation energy). The resulting value 428±16 kJ mol−1 is good accord with previous predictions based upon similar energetic determinations benzo- and phenylcyclobutadiene.

Infrared photodissociation (IRPD) spectra are reported for a proline–chloride anion cluster along with its d2- and d7-isotopomers. The spectral data indicate that proline is in neutral form as opposed to zwitterion, computations agreement some conformers energetically low-lying reproduce the observed spectra. Zwitterionic predicted be essentially stable ones should significantly populated; however, there no evidence these structures IRPD An exploration of potential energy surface loss...

A series of highly reactive metal-free chiral phosphoric acids possessing positively charged phosphonium ion substituents are reported and have been applied to Friedel-Crafts alkylations indoles 2,2,2-trifluoromethyl aryl ketones. These catalysts orders-of-magnitude more active similar or better enantioselectivities than their noncharged analogues. High tolerance a range substrates with electron-withdrawing electron-donating was also observed.

A series of methylated and octylated pyridinium quinolinium containing thiourea salts with a chiral 2-indanol substituent are reported. These organocatalysts positively charged analogues privileged bis(3,5-trifluoromethyl)phenyl substituted thioureas, found to be much more active catalysts despite the absence an additional hydrogen bond donor or acceptor site (i.e., presence heteroatom-hydrogen heteroatom). Friedel-Crafts reactions trans-β-nitorostyrenes indoles examined, good yields...