Effect of 4-t-butyl and other 4-substituents on rate constants for reactions of 1,1-disubstituted cyclohexanes and piperidines. 4-t-Butyl derivatives as valid reactivity models in the kinetic method of conformational analysis of cyclohexanes

1976 ◽  
pp. 838 ◽  
Author(s):  
David R. Brown ◽  
Philip G. Leviston ◽  
James McKenna ◽  
Jean M. McKenna ◽  
Raymond A. Melia ◽  
...  
Keyword(s):  
Conformational Analysis ◽  
Rate Constants ◽  
Kinetic Method

scholarly journals A kinetic method for the study of solvent environments of thiol groups in proteins involving the use of a pair of isomeric reactivity probes and a differential solvent effect. Investigation of the active centre of ficin by using 2,2'- and 4,4'- dipyridyl disulphides as reactivity probes

1980 ◽  
Vol 185 (1) ◽  
pp. 217-222 ◽  
Author(s):  
J P G Malthouse ◽  
K Brocklehurst
Keyword(s):  
Dielectric Constant ◽  
Physicochemical Properties ◽  
Solvent Effect ◽  
Rate Constants ◽  
Kinetic Method ◽  
Thiol Group ◽  
Analogous Reaction ◽  
Thiol Groups ◽  
Active Centre ◽  
Effect Of Solvent

1. Whereas the second-order rate constants for the reaction of the thiolate ion of 2-mercaptoethanol with 4,4'-dipyridyl disulphide (k4PDS) and with 5,5'-dithiobis-2-nitrobenzoate dianion increase with decreasing dielectric constant of the solvent, or remain unchanged, the rate constant for the analogous reaction with 2,2'-dipyridyl disulphide (k2PDS) decreases. This anomalous solvent effect and other unusual physicochemical properties of 2,2'-dipyridyl disulphide are discussed. 2. The differential effect of solvent on the reactions of thiolate ion with the 2,2'- and 4,4'-dipyridyl disulphides is shown to provide a method of characterizing solvent environments of thiol groups in proteins by a reactivity-probe method that should not suffer from the usual drawback associated with the existence of steric or binding effects of unknown magnitude. Application of the method to ficin (EC 3.4.22.3) suggests that its active-centre thiol group resides in a relatively hydrophobic environment. 3. The pH-k profile for the reaction of ficin with 4,4'-dipyridyl disulphide is reported.

scholarly journals On the importance of atmospheric loss of organic nitrates by aqueous-phase ·OH-oxidation

2020 ◽  
Author(s):  
Juan Miguel González-Sánchez ◽  
Nicolas Brun ◽  
Junteng Wu ◽  
Julien Morin ◽  
Brice Temime-Rousell ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Rate Constants ◽  
Water Solubility ◽  
Kinetic Method ◽  
Organic Nitrates ◽  
Condensed Phases ◽  
Alkyl Nitrates ◽  
Oxidation Reactivity ◽  
Atmospheric Loss

Abstract. Organic nitrates are secondary species in the atmosphere. Their fate is related to the chemical transport of pollutants from polluted areas to more distant zones. While their gas-phase chemistry has been studied, their reactivity in condensed phases is far from being understood. However, these compounds represent an important fraction of organic matter in condensed phases. In particular, their partition to the aqueous-phase may be especially important for oxidized organic nitrates for which water solubility increase with functionalization. This work has studied for the first time the aqueous-phase ·OH-oxidation kinetics of 5 alkyl nitrates (isopropyl nitrate, isobutyl nitrate, 1-pentyl nitrate, isopentyl nitrate and 2-ethylhexyl nitrate) and 3 functionalized organic nitrates (α-nitrooxyacetone, 1-nitrooxy-2-propanol and isosorbide 5-mononitrate) by developing a novel and accurate competition kinetic method. Low reactivity was confirmed, with kOH (at 296 ± 2 K) ranging from 8·107 to 2.5·109 L mol−1 s−1. Using these results, the previously developed aqueous-phase Structure Activity Relationship (SAR) was extended, and the resulting parameters confirmed the extreme deactivating effect of the nitrate group, up to two adjacent carbon atoms. The achieved extended SAR was then used to determine the ·OH-oxidation rate constants of 49 organic nitrates, including hydroxy nitrates, ketonitrates, aldehyde nitrates, nitrooxy carboxylic acids and more functionalized organic nitrates such as isoprene and terpene nitrates. Their multiphase atmospheric lifetimes towards ·OH-oxidation were calculated using these rate constants, and compared to their gas-phase lifetimes. Large differences were observed, especially for polyfunctional organic nitrates: for 50 % of the proposed organic nitrates for which ·OH-reaction occurs mainly in the aqueous-phase (more than 50 % of the overall removal) their ·OH-oxidation lifetimes increased by 20 % to 155 % under cloud/fog conditions (LWC = 0.35 g m−3). In particular, for 83 % of the proposed terpene nitrates, the reactivity towards ·OH occurred mostly (> 98 %) in the aqueous-phase while for 60 % of these terpene nitrates their lifetimes increased by 25 % to 140 % compared to their gas-phase reactivity. We demonstrate that these effects are of importance under cloud/fog conditions, but also under wet aerosol conditions, especially for the terpene nitrates. These results suggest that taking into account aqueous-phase ·OH-oxidation reactivity of biogenic nitrates is necessary to improve the predictions of their atmospheric fate.

Pulse radiolysis of aqueous solutions of N-Vinylpyrrolidin-2-one and Poly(N-vinylpyrrolidin-2-one)

1981 ◽  
Vol 34 (7) ◽  
pp. 1423 ◽  
Author(s):  
JE Davis ◽  
DF Sangster ◽  
E Senogles
Keyword(s):  
Aqueous Solutions ◽  
Hydroxyl Radical ◽  
Absorption Spectra ◽  
Rate Constant ◽  
Rate Constants ◽  
Pulse Radiolysis ◽  
Kinetic Method ◽  
Transient Species ◽  
Radical Scavengers ◽  
Dilute Aqueous Solutions

The absorption spectra of transient species produced when dilute aqueous solutions of N-vinylpyrrolidin-2-one (vp) and poly(N- vinylpyrrolidin-2-one) (pvp) are subjected to pulse radiolysis in the presence and absence of radical scavengers have been obtained and compared with those obtained from analogous compounds. The precise structure of the transients has not been established. Rate constants for the reaction of the hydroxyl radical with vp and pvp have been evaluated both by a competition kinetic method and by direct observation of the build-up of transient species: k(vp+·OH) = (6.4-8.1) × 109 dm3 mol-1 s-1 and k(pvp+·OH) = (1.5-2.3) × 108 dm3 mol-1 s-1 at 25°C. The rate constant for the reaction of the hydrated electron with vp has been determined as(1.6�0.3) × 109 dm3 mol-1 s-1 at 25°C. Rate constants for decay of the transient species have also been evaluated at 25°C: 2k(vp- OH·) = (8.1�1.0)× 108 dm3 mol-1 s-1; 2k(vp-e-) = (1.7�0.2) × 109 dm3 mol-1 s-1 and 2k(pvp-OH·) = (1.5�0.2) × 108 dm3 mol-1 s-1.

scholarly journals On the importance of atmospheric loss of organic nitrates by aqueous-phase ●OH oxidation

2021 ◽  
Vol 21 (6) ◽  
pp. 4915-4937
Author(s):  
Juan Miguel González-Sánchez ◽  
Nicolas Brun ◽  
Junteng Wu ◽  
Julien Morin ◽  
Brice Temime-Roussel ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Rate Constants ◽  
Water Solubility ◽  
Kinetic Method ◽  
Liquid Water Content ◽  
Organic Nitrates ◽  
Condensed Phases ◽  
Alkyl Nitrates ◽  
Oxidation Reactivity

Abstract. Organic nitrates are secondary species in the atmosphere. Their fate is related to the chemical transport of pollutants from polluted areas to more distant zones. While their gas-phase chemistry has been studied, their reactivity in condensed phases is far from being understood. However, these compounds represent an important fraction of organic matter in condensed phases. In particular, their partition to the aqueous phase may be especially important for oxidized organic nitrates for which water solubility increases with functionalization. This work has studied for the first time the aqueous-phase ⚫OH-oxidation kinetics of four alkyl nitrates (isopropyl nitrate, isobutyl nitrate, 1-pentyl nitrate, and isopentyl nitrate) and three functionalized organic nitrates (α-nitrooxyacetone, 1-nitrooxy-2-propanol, and isosorbide 5-mononitrate) by developing a novel and accurate competition kinetic method. Low reactivity was observed, with kOH ranging from 8×107 to 3.1×109 L mol−1 s−1 at 296±2 K. Using these results, a previously developed aqueous-phase structure–activity relationship (SAR) was extended, and the resulting parameters confirmed the extreme deactivating effect of the nitrate group, up to two adjacent carbon atoms. The achieved extended SAR was then used to determine the ⚫OH-oxidation rate constants of 49 organic nitrates, including hydroxy nitrates, ketonitrates, aldehyde nitrates, nitrooxy carboxylic acids, and more functionalized organic nitrates such as isoprene and terpene nitrates. Their multiphase atmospheric lifetimes towards ⚫OH oxidation were calculated using these rate constants, and they were compared to their gas-phase lifetimes. Large differences were observed, especially for polyfunctional organic nitrates: for 50 % of the proposed organic nitrates for which the ⚫OH reaction occurs mainly in the aqueous phase (more than 50 % of the overall removal), their ⚫OH-oxidation lifetimes increased by 20 % to 155 % under cloud/fog conditions (liquid water content LWC = 0.35 g m−3). In particular, for 83 % of the proposed terpene nitrates, the reactivity towards ⚫OH occurred mostly (>98 %) in the aqueous phase, while for 60 % of these terpene nitrates, their lifetimes increased by 25 % to 140 % compared to their gas-phase reactivity. We demonstrate that these effects are of importance under cloud/fog conditions but also under wet aerosol conditions, especially for the terpene nitrates. These results suggest that considering aqueous-phase ⚫OH-oxidation reactivity of biogenic nitrates is necessary to improve the predictions of their atmospheric fate.

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