Analysis of Solute/Solvent Interactions for the Acidity of Acetic Acids by Theoretical Descriptors

Headley, Allan D.; Starnes, Stephen D.; Wilson, Leland Y.; Famini, George R.

doi:10.1021/jo00105a020

Cited by 44 publications

(26 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, the possible intramolecular hydrogen bond between the carboxyl group and the methoxy oxygen would increase the deprotonation energy (or decrease the gas-phase acidity) of CH 3 OCH 2 CO 2 H. The reversed acidity order was also found between C 6 H 5 OCH 2 CO 2 H and C 6 H 5 SCH 2 CO 2 H. Our calculations show that C 6 H 5 SCH 2 CO 2 H (⌬H acid ϭ 335.7 kcal/mol) is a stronger gas-phase acid than C 6 H 5 OCH 2 CO 2 H (⌬H acid ϭ 338.6 kcal/mol). While in DME, C 6 H 5 OCH 2 CO 2 H (pK a ϭ 8.3) is a stronger acid than C 6 H 5 SCH 2 CO 2 H (pK a ϭ 8.6) [6]. Similar to the above analysis, both the less polarizable oxygen and the possible intromolecular hydrogen bond are responsible for the lower gas-phase acidity of C 6 H 5 OCH 2 CO 2 H.…”

Section: Figure 2 Plots Of Ln([asupporting

confidence: 61%

“…A recent study of natural food flavors found that MTA is one of the biotransformation products of the cysteine-aldehyde conjugate by baker's yeast [4]. MTA has a similar structure as that of methoxyacetic acid, CH 3 OCH 2 CO 2 H. Both methoxyacetic acid and MTA have been used to study solvent and substituent effects on the acidity of substituted acetic acids [5,6]. In aqueous solution, MTA (pK a ϭ 3.7) is a slightly weaker acid than methoxyacetic acid (pK a ϭ 3.5) [6].…”

mentioning

confidence: 99%

“…MTA has a similar structure as that of methoxyacetic acid, CH 3 OCH 2 CO 2 H. Both methoxyacetic acid and MTA have been used to study solvent and substituent effects on the acidity of substituted acetic acids [5,6]. In aqueous solution, MTA (pK a ϭ 3.7) is a slightly weaker acid than methoxyacetic acid (pK a ϭ 3.5) [6]. In the gas-phase, methoxyacetic acid has an acidity (⌬H acid ) of 341.9 kcal/mol [7,8], while the acidity of MTA is unknown.…”

mentioning

confidence: 99%

See 2 more Smart Citations

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Ren

Patel

2005

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

We determined the gas-phase acidity of methylthioacetic acid (MTA) in a triple-quadrupole mass spectrometer using the Cooks' kinetic method with the consideration of entropy effects. The negatively charged proton-bound dimers were generated by electrospray ionization. Collisioninduced dissociation was applied to the dimer ions and the product ion ratios were measured at four different collision energies. The gas-phase acidity (⌬H acid ) of MTA was determined to be 340.0 Ϯ 1.7 kcal/mol using the extended kinetic method and 339.8 Ϯ 1.7 kcal/mol using the standard kinetic method. The entropy term is insignificant in this case and can be ignored. The standard kinetic method yielded a free energy of deprotonation of MTA (⌬G acid ) of 333.0 Ϯ 1.7 kcal/mol. The entropy of the acid dissociation, ⌬S acid , was estimated to be 22.8 cal/mol K. Theoretical prediction at the B3LYP/6-31 ϩ G* level of theory gives a similar value for ⌬H acid of 338.9 kcal/mol. In the gas-phase, MTA is a stronger acid than methoxyacetic acid, although in solution, MTA is a weaker one. , and as a model to study electron-transfer reactions in substituted alkyl sulfides [3]. A recent study of natural food flavors found that MTA is one of the biotransformation products of the cysteine-aldehyde conjugate by baker's yeast [4]. MTA has a similar structure as that of methoxyacetic acid, CH 3 OCH 2 CO 2 H. Both methoxyacetic acid and MTA have been used to study solvent and substituent effects on the acidity of substituted acetic acids [5,6]. In aqueous solution, MTA (pK a ϭ 3.7) is a slightly weaker acid than methoxyacetic acid (pK a ϭ 3.5) [6]. In the gas-phase, methoxyacetic acid has an acidity (⌬H acid ) of 341.9 kcal/mol [7,8], while the acidity of MTA is unknown. In this paper, we report on the first determination of the gas-phase acidity of MTA by using the Cooks' kinetic method [9,10] and theoretical calculations. ExperimentalThe gas-phase acidity (⌬H acid ) of MTA was determined by using the extended Cooks' kinetic method in which entropy effects were taken into consideration [11][12][13]. Selected applications of using the extended kinetic method to determine thermochemical quantities can be found in the current literature [14 -19]. Briefly, a series of proton-bound dimers ([A·H·A i ] Ϫ ) of deprotonated MTA (HA) with a set of conjugate bases of reference acids (HA i ) were generated in the mass spectrometer. The reference acids all have known gas-phase acidities. Each proton-bound dimer was activated by collisions with argon atoms and underwent competitive unimolecular dissociations to produce two ionic products, A Ϫ and A i Ϫ , with rate constants of k and k i , respectively, Scheme 1.With the assumption that there are no reverse activation barriers for both dissociation channels, the natural logarithm of the ratio of the rate constants can be expressed by eq 1, where R is the ideal gas constant, T eff is the effective temperature of the activated dimer ion, and ⌬H and ⌬H i are the gas-phase acidities of MTA and the reference acid, respective...

show abstract

Section: Figure 2 Plots Of Ln([asupporting

confidence: 61%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Ren

Patel

2005

J. Am. Soc. Mass Spectrom.

View full text Add to dashboard Cite

show abstract

“…24,25 Experimental values needed in the LSERs are oftentimes not available; therefore, Theoretical Linear Solvation Energy Relationship (TLSER) descriptors were developed based on LSER parameters for related compounds. TLSER descriptors have been found to account fairly well for acidity 26 and some toxicological indices. 27 Moreover, it has been found that molecular electrostatic potential (ESP) parameters are good descriptors of octanol/water 28 and noncovalent interactions.…”

Section: ' Materials and Methodsmentioning

confidence: 99%

Probing the Primary Mechanisms Affecting the Environmental Distribution of Estrogen and Androgen Isomers

Qiao

Carmosini

et al. 2011

Environ. Sci. Technol.

View full text Add to dashboard Cite

Land application of animal manure has been identified as a source of natural and synthetic hormone contaminants that are frequently detected down-gradient of agricultural operations. Much research on the environmental fate of hormones has focused on the structural isomers most biologically active in mammals, e.g., the 17β-isomers of the estrogen estradiol (E2) and the synthetic androgen trenbolone (TB). However, recent work has shown that the Rand β-isomers of E2 and TB can cause comparable effects on certain aquatic species. To improve our understanding and ability to predict isomer-specific interactions with environmental sorbents, we measured the association (K DOC ) of the Rand β-isomers of E2 and TB as well as their primary metabolites (estrone and trendione) with two commercial dissolved organic carbon (DOC) sources by measuring both free and DOC-bound hormone concentrations. We also measured solventÀwater partition coefficients partitioning (K SW ) for the same hormones using hexane, toluene, and octanol. Log K DOC * , log K OC (OC-normalized sorption by soils), and K OW values are all greater for the β-isomer except between the E2 isomers. Theoretical descriptors reflecting electronic character and soluteÀsolvent interactions were calculated to elucidate isomer-specific behavior. Trends for log K OW and log K DOC among hormones as well as between isomers are explained reasonably well by computed electrostatic potential and H-bonding parameters.

show abstract

“…Buffer ratio is 1:1 (base:acid) and pH = 9.34 AE 0.04 a The numbers in parentheses are standard errors based on a least-squares fit of the kinetic data using Eqn. (9). b k nuc = 10k 2nd , the rate effect of the protonated amine in this concentration range is expected to be negligible.…”

Section: From Base-catalysed Hydrolysis To Nucleophilic Substitutionmentioning

confidence: 96%

General‐base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions

Buurma

Blandamer

Engberts

2003

J of Physical Organic Chem

View full text Add to dashboard Cite

General-base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions Buurma, NJ; Blandamer, MJ; Engberts, Jan; Buurma, Niklaas J. Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. ABSTRACT: The reactivity of 1-benzoyl-3-phenyl-1,2,4-triazole (1a) was studied in the presence of a range of weak bases in aqueous solution. A change in mechanism is observed from general-base catalysed hydrolysis to nucleophilic substitution and general-base catalysed nucleophilic substitution. A slight tendency is also observed for the more hydrophobic general bases to show higher reactivity towards 1a. Aspartame is an effective nucleophile, possibly because nucleophilic substitution is subject to intramolecular general-base catalysis. A general conclusion derived from the present results is that unexpected rate effects can only be rationalised provided that the detailed reaction mechanisms are well understood. Copyright  2003 John Wiley & Sons, Ltd.KEYWORDS: hydrolysis; changes in mechanism; general-base catalysis; general-acid catalysis; nucleophilic substitution INTRODUCTIONThe hydrolysis reaction of the activated amide 1-benzoyl-3-phenyl-1,2,4-triazole (1a) is general-base catalysed (Scheme 1). 1In highly aqueous solutions, the concentration of water is sufficiently high for water to act (detectably) as both a general base and a nucleophile. Hence, in the absence of other general bases, the water-catalysed (i.e. pHindependent) hydrolysis is the sole reaction. In the presence of sufficiently basic cosolutes, the watercatalysed reaction is unimportant. More basic cosolutes are much more effective catalysts for hydrolysis than water. Consequently, despite the relatively low molality of added general bases, the general-base catalysed hydrolysis pathway competes with the water-catalysed pathway. It is stressed that even though in the watercatalysed reaction the second water molecule in the activated complex (i.e. B = H 2 O, Scheme 1) acts as a general base, a distinction is drawn between the watercatalysed reaction and general-base catalysed reaction.Increased basicity of cosolutes usually leads to a concomitant increase in nucleophilicity. This increase in nucleophilicity provides an alternative reaction pathway: nucleophilic attack on the carbonyl functionality, followed by loss of the (substituted) 1,2,4-triazole leaving group (Scheme 2).In this mechanism, the nucleophilic water molecule is replaced by a stronge...

show abstract

Analysis of Solute/Solvent Interactions for the Acidity of Acetic Acids by Theoretical Descriptors

Cited by 44 publications

References 2 publications

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Determination of the gas-phase acidity of methylthioacetic acid using the Cooks’ kinetic method

Probing the Primary Mechanisms Affecting the Environmental Distribution of Estrogen and Androgen Isomers

General‐base catalysed hydrolysis and nucleophilic substitution of activated amides in aqueous solutions

Contact Info

Product

Resources

About