Alkaline hydrolysis and nuclear magnetic resonance spectra of some thiol esters

Abstract

The alkaline hydrolysis rate constants at 35°in 40% aqueous p-dioxane and the nmr chemical shifts have been measured for nine thiolacetates, CH3COSIV, nine methyl thiol esters, RCOSCHj, and seven disubstituted thiol esters, RCOSIV. Alkaline hydrolysis rate constants are controlled almost exclusively by steric effects of the R and R' groups. The nmr substituent chemical shifts (SCS) of thiol esters are controlled largely by steric and sixnumber effects of the R and IV groups. All of these correlations are discussed and compared with correlations previously reported for similar oxygen esters, RCOOR', on the basis of differences in various structural features of the two series. A contributing structure involving negative charge development at the sulfur atom is apparently not of importance for simple thiol esters.

Mechanism of action of clostridial glycine reductase: isolation and characterization of a covalent acetyl enzyme intermediate

“…All radioactive material remained protein bound after 9 h at 25 °C in 0.5 N HC1. Furthermore, when the labeled protein was incubated in 0.5 M Na2C03, pH 11.5, at 25 °C, the apparent first-order rate constant for hydrolysis of the acetyl group was 1.2 X 10~2 min"1, consistent with the rate of hydrolysis of thioesters (5 X 10'2 min'1, for CH3COSCH2CH3 and 4 X 10'2 min'1 for CH3COSCH2C-H2CH3 at 35 °C, 10 mM NaOH) (Idoux et al, 1973). The complex was also treated with KBH4.…”

Computational Studies of the Aminolysis of Oxoesters and Thioesters in Aqueous Solution

“…The greater reactivity of thioesters than oxoesters in the nucleophilic addition step is consistent with the smaller degree of hyperconjugation or resonance contribution of the sulfur lone electron pair onto the carbonyl carbon compared to the bridging oxygen of an oxoester. , NBO calculations were performed at the HF/6-31G* level to evaluate the change of C−X bond order (Lowdin bond order) between reactants and transition states in the first step of the stepwise mechanisms . These calculations show that for the oxoester the bond order is decreased by 0.166, while for the thioester the bond order change is only 0.127 .…”

Proximity effects. 2. Conformational influence of nonacyl groups on acyl group properties in N-monosubstituted amides and in other carboxylic acid derivatives: a 7-position proximity effect

“…In order to assess this consideration, we have carried out an additional correlation using the hydrogen-7 number as a steric "correction site" parameter to obtain SCS = -0.37 + 4.80 * + 1.15£sc + 0.44(H-7no. ), (>0.500) (0.09) (<0.001) £2 = 90.8%, s = 0.71 (9) As in eq 1-4, the t test indicates that * is the least significant variable. Rejection of this variable yields SCS = -0.73 + 1,53£sc + 0.48(H-7no.…”

“…The effect of the A;-alkyl group on the N-H stretching frequency is general for these various amide series. That is, in each case the N-Me compound exhibits the highest > • The N-z-Bu compound's pnh is always next highest (7)(8)(9)(10)(11) cm-"1 less than the N-Me), the N-Et, N-zz-Pr, and N-zz-Bu occur next as a group (12-21 cm-1 less than the N-Me), and the N-z-Pr, N-s-Bu, and -í-Bu occur Journal of the American Chemical Society j 99:14 / July ') for N-Monosubstituted Amides, RCONHR'0 as a group at the lowest frequency (23-31 cm-1 less than the N-Me). With the exception of the z-nh for the N-z-Bu compounds, these results can be rationalized fairly well in terms of the ability of R' to inductively stabilize a contributing structure such as III (a form favoring a lower frequency ) relative to a structure such as II.…”